ARC Racing

FTS Tire Treatments

2011-10-24T07:54:00.000-04:00

F.T.S. Fast Tire Solutions Tire Treatment

By Travis Mims

I am often asked which treatment is best for a particular track or situation, and since I am not an experienced racer and have a ton to learn on this subject, I thought I would research F.T.S. and their products and see if I could make some sense out of the mysterious alchemy of tire prepping. After reading their information on their website and working with some of their products I, and a whole lot of questions to Tom and Hunter and Jody, it actually starts to make some sense. In fact, the guys at F.T.S. have taken much of the guesswork out of choosing the proper prep. To begin with, there are only two basic choices for the initial treatments, Hard Track (HT Series) and Tacky Track (TT Series) It is up to you to decide the prevailing condition of your track, and don’t make the mistake of visualizing your favorite tracks' ideal condition. Try and give an honest opinion of the condition most likely to be encountered. I asked about the definition of Tacky and for the purpose of tire treatments, it can describe anything from damp, soft, wet, loose or sandy. Simply put, anything that is not dry and hard will be better suited with TT treatments. I think that the Hard Track is self explanatory from dirt to clay to asphalt.

Now that we have HT Series and TT Series understood and what type of surface they apply to, it is time to treat some tires. For this, let’s pretend that we have a new set of tires and they have been cut, sanded, stroked, sacrificed to and whatever else is done before they are mounted or chemically treated. Both HT and TT have an Inside Solution that is designed to be cold rolled from 18-36 hours inside the tires with 1-3 oz. of prep in each tire. The more prep that is put inside (and/or outside) the tire, the greater the effect will be from that prep. The middle of the road is 2 oz. in the LF and RS tires and 1 oz. in the LR. The LR should always be the hardest tire on the kart with the least “bite” and the LF should always be the softest with the most “bite”. “Bite” is a loose term used to describe the grip a tire will provide when a given prep is used. After the initial inside treatment, depending on circumstances, you may be finished with inside prep. Now you want to begin to treat the outside of your tires. There are four products available, HT Series1, HT Series 2, and TT Series1, and TT Series 2. Depending on which choice you made (HT or TT) you can begin to treat the outside with either 1 or 2. *REMEMBER* Series 2 is stronger and more aggressive than 1 in both HT and TT products. There is not room here to try and describe all the different techniques in use. One technique that I observed is that after the inside treatment, the tires were kept in a shaded cool environment and given a once a day wipe with either Series 1 or Series 2. That was started 7 to 10 days before race day.

I also know that some will do another cold roll inside treatment 3 - 5 days pre-race if they are not satisfied with the tires progress. I am blown away at how someone can smell and feel and squeeze and judge tire differences and can usually tell you to within a point what a durometer will read. To those that may not know, a durometer is basically a gauge that has a pointed tip that is pressed into a tire a short pre-determined distance and it gives a number reading on how easy (or how hard) it was to do so. It is useful in that it gives a person a scale to go by when comparing effectiveness of different treatments.

The softness of a tire dictates the optimum operating temperature of the tire; IT DOES NOT NECESSARILY DEFINE HOW MUCH BITE A TIRE HAS. You soften a tire to match temperature conditions. Colder conditions will usually warrant a softer tire, and conversely, hotter conditions will require a harder tire.

That is the bulk of the F.T.S. Lineup and it covers a wide range of uses. But what do you do on race day when you need some more bite from your tires? You break out the F.T.S. Slight Bite or the F.T.S. Black Bite. These two products are designed to be outside wipes and can be effective on both hard and wet tracks. They are not abrasive and both will give you more bite in your tires. Black Bite is the more aggressive of the two. The instructions say that both can be used for "firing a tire" which simply means adding extra bite initially to help bring the tire up to its operating temperature. Remember, you add pre race wipe to give the tire initial grip, or “bite” to make up for lack of bite in the track itself. Use more when the track has less bite, and less when the track has more bite. Normally, dirt tracks gain bite as they “come-in,” a term used to describe a track that is gaining grip as more and more karts lay down rubber and or the sun and heat bakes the clay. If calcium chloride is put on the track prior to the race, expect the track to be slick until the track starts to come-in. Once a calcium track comes-in, it will have considerably more bite than the same track would if calcium was not used, and it will remain more consistent until weather conditions change (night comes) or it starts to dry out and break up.

All of the above can be used on all the types and brands of racing tires on the market. There is, however, one brand of tire that warrants its own witch's brew. I am talking about the Maxxis EL of course. No matter if you love it or hate it, it is a fact of life for racers in some regions and classes and tracks. Fast Tire Solutions has approached the EL tire with 2 products; the first is EL Elite Inside, for inside cold rolling. The second is EL Elite Conditioner which can be used as both a tire roll and an outside wipe. Slight Bite and Black Bite are then used at the track to “fire off” the tire. (Check out ARC's catalog items 9860 and 9861 for a proven EL tire prep formula using F.T.S. products)

Last, but not least is Fast Tire Solutions Tire Wash. It is water based cleaner that comes with its own spray bottle and it cleans rubber as well as anything, but will not destroy the tire treatments used on the tire. Everyone knows that tire cleaning is just a part of life when racing dirt tracks and FTS Tire Wash can be used either with or without water and wiped dry. It can be used with any of Fast Tire Solutions' products.

Tire treatments for the Maxxis EL Tire

- EL Elite Inside

- EL Elite Conditioner

Tire Treatments for other kart tires.

Hard Track              Tacky Track

- HT Inside              TT Inside

- HT Series 1           TT Series 1

- HT Series 2           TT Series 2

Pre-Race Wipes and Tire Cleaner

- FTS Slight Bite
- FTS Tire Wash
- FTS Black Bite

Clone Stock Appearing Outlaw Rules

2011-09-26T12:47:00.001-04:00

The following rules are something I wrote up last fall for tracks to use as a template for a stock appearing class for the clone engine. Thease rules are intended to allow the average guy to build a powerful yet still durable engine in his own garage while keeping a lid on the potential costs of high priced modifications. Stock appearing has always been my favorite class because it is not so riddled with rules and it makes enough power to keep things exciting.

******************************************************************************************

From 6 feet away, the engine, unless otherwise noted, must appear like a BSP, or Harbor Freight 6.5 HP engine. Parts may be interchanged between engine types.

Internally, you can change whatever you want as long as it meets the restrictions below. The restrictions are only for safety, cost control and containing performance to provide reasonable durability expectations.

Fuel tank must be relocated and a fuel pump, pulsed from anywhere on valve cover or crankcase, may be used.

Any throttle mechanism allowed that works with the stock throttle shaft’s bell crank. Remaining stock throttle mechanism parts may be removed.

Fuel is methanol only. (or gas only***track option***) A pump-a-round or similar community fuel pool is encouraged.

A plate may be bolted to the top of the engine to mount fuel pumps and/or throttle mechanisms.

Choke may be removed from carb. If removed, choke shaft hole must be plugged.

Pull starter may be replaced with a flywheel cover and any electric starter nut may be employed.

Aftermarket air filter adapter with a max length of 1.375” is allowed. Air filter may be up to 8” long.

Any header is allowed. No muffler unless required by track. If required use RLV-4106.

Unaltered SFI certified billet flywheel mandatory with stock ignition module only.

No welding or addition of material of any kind (e.g. epoxy) to the head, side cover, block or carb.

*Stage 2 Tech: In addition to the above, remove valve cover and check:

Rockers, pushrods, valves and valve spring retainers must appear stock. Valves and retainers may be used in any combination on either side. (e.g. exhaust valve, retainer and lash cap on intake side)

Max lift taken off the top of the valve spring retainer is .280”

*Stage 3 Tech: In addition to the above, remove head and check:

Piston must be flat top or dished and may not pop up above deck.

Max cylinder bore is .035” over stock bore. Stock bore is 2.685"

Valve head diameters must be between .940” and .990” and must appear stock

Max Stroke is 2.133” taken from top of piston

NEW ARC Dual Bearing Billet Sidecover for GX200 and Clone

2011-09-13T10:15:00.000-04:00

The long-anticipated 6057 Billet Aluminum Sidecover is now available at $139.98 MSRP. Not only does this sidecover look great, but it adds structural integrity to the block, increasing engine durability.

Features include:

Side-by-side dual ball bearings for the crank main journal, adds an additional fulcrum point to reduce crankshaft flex.
Perimeter O-ring, seals to block
4 dowel-pin holes with solid dowell pins that pick up the additional dowel-pin holes in the block, greatly increases mating shear strength
Ball bearing support for the camshaft main, increases strength and minimizes potential for wear
Oil drain hole with removable 1/4"NPT plug.
2 Venting/pulse holes at the very top with 1/8"NPT plugs.
2 Oil fill ports with billet aluminum hand-tightened plugs
Threaded holes over side dowel-pins so small bolts (included) can be used to push the sidecover for easy removal.
Includes bolts and crank seal.

The New 6934 ARC Air Filter Adapter for GX200, GX160, and Clone engines.

2011-03-25T15:11:00.000-04:00

Here is the new air filter adapter I have been giving y'all sneak peeks of on ARC's facebook. It is for the clone and GX200 type engines.

This thing is has been in development for a long time and has gone through so many different prototypes that I've lost count.
*Meets the rule specs for AKRA/WKA Box Stock and BP
*Out-flows anything else available on the market today by a substantial margin.
*Attaches to the carb using custom made, counter sunk socket nuts (don't lose them, they are expensive). This design allows us to hide the studs and nuts from the incoming air flow, reducing turbulence.

*100% CNC milled design...it never sees a turning machine because the contours both inside and outside cannot be made on a turning machine.

*The flange for the air filter is a slightly smaller diameter allowing a "street elbow" to be easily attached for Road Racing.

They will be available on our website later today. We only have a limited number of socket nuts until Tuesday 3/29, but then we will be loaded to the hilt.

Special note: The thick, rubber coated metal gasket that goes between the carb and the adapter is mandetory. Most of the more recent Harbor Freight engines have a paper gasket instead. You will need to buy one in this case and they can be found here

A Few Changes for 2011

2011-01-20T08:12:00.000-05:00

For the most part, our GX200 and Clone engine kits and parts kits will no longer include exhaust components. Since different places and classes have different header/muffler requirements, we decided to remove these items from the kits effected by this. When this is the case, we have added our recommended exhaust components as seperate "Related Items" at the bottom of each kit's main description page. We did this to help you buy what fits YOUR specific and individual needs.

We are working every day to add more and more of the parts we carry to our website. Additionally, we are working to make the site more organized and to provide complete descriptions to items.

We recently introduced some new items. We now manufacture a hardened chromolly billet crankshaft for the model 28 Briggs & Stratton Lawnmower engine. We also just introduced 5-3/4" diameter(aka 3hp diameter) SFI certified billet flywheels for the Honda GX160, GX200, GX340, and GX390 engines, and their clone counterparts in both finned, and non-finned designs. All of these models incorporate ARC's adjustable ignition timing hub and utilize the stock coil via a coil bracket (sold seperately). These flywheels are bolt-on items, requiring no block modifications, and their light weight and small diameter make them the top performers on these engines when the stock ignition system is utilized.

We also have one more new part for the GX200 clone engine that will be introduced shortly. It is something we have had on the back burner, waiting for the right opportunity for release.

Check out our Facebook page!

2010-11-19T14:55:00.002-05:00

If we have helped you and you want to know quick what is happening at ARC, then please, come and join our Facebook page.
ARC Racing on Facebook

Checking Ignition Timing for the 2011 Box Stock Rules

2010-11-18T17:30:00.001-05:00

Set up a degree wheel with a pointer to find Top Dead Center.

Roll the flywheel until the right-hand edge of the metal magnet cover just bumps a straight edge held against the right-hand edge of the right-hand coil leg.

Here it is from a slightly different angle without the straight edge.

Now just read the degree wheel.

This flywheel is in tolerance because it is set at 15° BTDC (counter clock-wise rotation) which is less than the 18° BTDC maximum allowed in the Box Stock rules.

Click HERE to download a paper degree wheel the perfect diameter for a GX200 engine. Paste it to cardboard and cut it out, then drill the center just big enough for your clutch bolt.

SPECIAL NOTE: For those using an ARC Billet Flywheel (such as Road Racers) "Stock" timing is 24° BTDC maximum with the flywheel positioned as pictured below.

Defining this Blog

2010-10-21T12:33:00.000-04:00

A blog is a "weB log." A cronological record of whatever the "blogger" wants to write. It is important to note that things change as time goes by. In racing in particular, technology is always a driving force that can sometimes change the application of things we knew (or thought we knew) in the past.

I can remember when going much quicker than a 10.90sec 1/8th mile in a Jr. Dragster was rarely even considered a possibility. Now kids must add ballast weight to slow their cars down so they do not go faster that the 7.90sec floor now imposted by NHRA in the 1/8th mile. Parts have changed so dramatically since those 10.90 days that what was once the epitome of the Jr. Dragster engines is now looked at as something for beginners.

So things change, and often that changes what we all once thought the future would be. So take what you read here and apply history to get a clear picture of why things are no longer the same. What is written here is not laws to govern our thoughts and ideas about the future, but more a record of what was.

Making a few changes to karttrax

2010-08-04T08:31:00.001-04:00

http://www.karttrax.com/ is now the landing page for our video webcast, live chat, and recorded video archive. The original link www.ustream.tv/channel/karttrax will continue to work as usual.

Finally...Parts are being added to our webstore!

2010-08-04T08:25:00.000-04:00

Thaks to the efforts of our new webstore manager, Travis Mims we are finally getting around to filling the shelves with all the parts that ARC offers. Our goal is to have every part we sell, with detailed descriptions on the webstore by year's end.
I built the webstore on a great software foundation, but simply did not have the available time to "stock the shelves." Travis has taken the ball and is charging hard toward the end zone.

Some great features of the store:

Ability search for parts by part number and keywords
Each part's detailed description allows us to relate complimentary parts (like bearings to their rod)
Ability to directly pay for and close out transactions using various credit cards and PayPal
Multiple shipping options

Travis is also monitoring incoming store orders more often during the day in order to shorten the time between when your order is placed and when it gets packaged and shipped. In most cases (unless something is out of stock) we will now ship your order the same day if it is placed before 12 PM EST M-F.

A final trick that I am trying to program is a popup window with exploded views of the various engines for which we stock parts. Ordering will be as simple as point and click. Cross your fingers and wish me luck on this, because it isn't easy.

I believe that as the store comes along, you will find it to be informative and easy to navigate toward your goal of getting the parts you need quickly.

Tom

Live Build Clinic Webcast from ARC Racing

2010-02-19T13:31:00.004-05:00

I am doing a series of LIVE interactive webcast videos covering various topics on engines and eventually other karting related stuff.

The series will be broadcast live on most Thursday evenings @ 7PM EST on Ustream at the following address:
http://www.ustream.tv/channel/karttrax

The shows will be recorded and stored on Ustream at this same address to watch anytime.

If you sign up with Ustream (free), you will be able to post questions in the Live Chat window adjacent to the video window. I will try to answer relevant questions as they are asked. I will be giving away a few items during the live show to viewers.

You will need a decent computer and probably at least a basic dsl internet connection to view the stream. Try one of the recorded shows before the live broadcast so you can get your computer all set to go beforehand.

Please email me with ideas for upcomming shows tom@arcracing.com

New stuff for the GX200 GX160 and 6.5 Clones

2010-02-04T08:42:00.004-05:00

We now have billet rods for the GX160, GX200 and 6.5 clones that are +.010"(#6269) and +.020"(6271) longer than our standard, stock-length billet rod (#6270). All remain $59.95
Other new in-stock items not yet on the E-store:
4° and 8° flywheel keys @ $7.50 each
Honda G200 18 pound valve springs @ $2 each
Honda ZOT piston ring sets in Std., +.010" and +.020" all @ $12/set
Honda Flat-Top ZOT Pistons in Std.@ $17 each,+.010"@ $20 each and +.020"@ $18 each
Honda Dished ZOT +.010" Pistons @$10 each

Dyno Cams new CL-1 Box Stock Cam $34.95

Pressure Chart for GX 200 Clone Valve/Spring/Retainer Combinations

2009-10-03T15:18:00.000-04:00

The following chart will help you select the correct valve/spring/retainer combination for your GX200 or Clone engine by providing the spring pressures and installed heights achieved with the various combinations. This chart is going to continue to provide further information. So check back!

http://www.arcracing.com/Valve_Spring_Chart.xls

Updated 10/3/09: Added Pressures for DJ-1055T Trick Stock Spring, BP Spring, and Dual Spring (Installed height for Dual Spring Retainers is not yet included.

The coil bind figures DO NOT necessarily mean you can run that much lift with the corresponding valve/retainer combo. YOU MUST check for clearance between retainers and valve guides, and clearance between valves and the piston.

Unconventional engine break-in theory.

2009-08-21T22:04:00.003-04:00

This is not "MY" break-in program. But it is basically what I believe. What I do is rooted in Motoman's Break-in procedure. He's a smart guy and his procedure, adapted to a kart engine, works for me.

The theory is that with the hard chrome faced rings, tight piston to wall clearances, and fine crosshatch found in cylinders today, you have a very short time to get the rings to seat right before the peaks of the cross hatch become worn too much to finish the job right.

I use 16 oz of 30wt non detergent oil (Shell ND 30wt)and I cover up the vents in the pull starter cage to build heat. Remember, we don't have oil filters, so we have to change oil often to remove the debris from the oil.
I break mine in on the dyno with several long, wide open throttle, hard runs after I get the engine up to temp.

Jetting a clone carb

2009-08-21T21:54:00.004-04:00

Here is what I have seen on my dyno:

If you are still running the stock air box:
A .029" is slightly better than a stock .028" If you are allowed to run the valvecover vent tube to a catch can and plug the hole in the airbox, do it.

If you are running Box Stock rules, only the main jet can be changed:
.037" to .039" seems to be the ticket at low altitude. .038" being my "go-to" jet.
When the engine is cool, a .037" makes more power on the top end and can help the engine turn more RPM, but most times, it is at the expense of HP at or about 4800 RPM. (you won't see that on anything other than a water-brake dyno)
A .039" almost totally gets rid of the mid range dip in HP, but it costs you on top end. A .038" is a compromise and once the engine gets good and hot, seems to run better than the .037"
Side note- On the road courses where we are running them 30 minutes wide open, we also drill the low-speed jet. to .019"-.020"

If you are running BP or Superbox, The etube and both jets can be changed:
I like the 140 etube, .036 jet and .019" to .020" low speed jet.

These have been my observations on on my dyno with the Yellow engine and the New Greyhound HF engine. My on-track experience has only been with the yellow engine.

Buret used to measure Cylinder head cc's

2009-08-11T07:40:00.002-04:00

I get asked alot where to buy a buret to measure the liquid accurately as it is poured into a cylinder head in order to measure cylinder head or combustion chamber cc's. This is the buret I use and it is only $20.

Poor Man's A/C

2009-07-29T16:05:00.001-04:00

It is really hot right now, and I thought I'd share a method I use to keep cool at the racetrack.

Get a small 6-pack cooler and fill it with ice. Pour in: 1 regular bottle of rubbing alcohol, 1/2 bottle of the green (menthol) rubbing alcohol, and 1/2 bottle of ammonia spirits (about 1/2 to 1 ounce). Add enough water to make it slushy so you can dip rags in it.

Dip in a rag, wring it out good, and wipe down your neck, face, arms, and legs. You can wrap the rag around your neck after that. Re-dip as needed.

Basically, the alcohol evaporates very quickly and cools you down faster than your sweat can, especially when it is very humid.

You may have to go to the pharmacy counter to find the amonia spirits (aka spirit of amonia).

I learned this trick at Suicide Circle Speedway from my buddy "Strolin" Jerry Nolan.

Racing the BSP at Roebling Road

2009-02-09T21:21:00.000-05:00

ARC Top Plate & Throttle Mechanism

2008-11-17T09:31:00.013-05:00

Our top plate/throttle mechanism (# DJ-1146 ) is CNC machined from 1/8" aluminum plate. All the parts for the throttle mechanism that do not come with an engine are included (cable # 2100A and jacket # 2100E , sold seperately). The throttle mechanism maximizes foot pedal travel giving you more precise throttle control. The plate is pre-drilled to accept the Mikuni fuel pump as shown in the video (P/N 6935 sold seperately) so the pump will accept the existing fuel hose provided with the engine. Below is an installation video.

Installing a BSP Restrictor Plate

2008-10-24T12:58:00.006-04:00

Take everything off to this point.

Put on a gasket.

Put on the restrictor plate.

Put on a second gasket.

Install the carb.

Install the Air filter adapter.

WRONG! The air filter adapter is installed upside-down.
Notice the blocked air oriface.

Splined Post for Jr. Dragster Torque-Converters

2008-09-26T11:56:00.003-04:00

For several years, ARC has been making billet crankshafts with splined PTO shafts to provide the added strength some of today's larger, more powerful cars require, but the availability of posts for various clutch assemblies has been limited. So we decided to make our own.

The main post is made of 7075 T6 Billet Aluminum. The replaceable collar is made of steel and is assembled to the post via piloted LEFT-HAND threads so the direction of resistence from the engine to the belt keeps the collar tight. Posts and collars will be available soon for ALL the major Torque-Converters used today.

ARC "Ported" Clone Air Filter Adapter

2008-09-19T08:26:00.003-04:00

Installed Correctly (click on picture for larger view)
Installed Upside-Down (click on picture for larger view)

For maximum performance, ARC's air filter adapter is ported to the low speed (left) and high speed (right) orifice jets. This is necessary because the funneled velocity stack design would otherwise cover these jets. Improper installation of the air filter adapter will partially cover, and impede flow to the orifice jets because they are not in the same position. The engine will spit and sputter and lack both bottom, and top end power if these orifice jets are blocked.

New and improved GX 340/390 flywheels

2008-07-15T09:10:00.002-04:00

The GX 340/390 engine has grown in popularity to the point that we were able to produce a more specific flywheel body to this engine. One major change is that these flywheels are designed to use the stock coil, and don't require any coil bracket. Both flywheels are SFI certified and have integral billet cooling fins.

We have two new models and they will replace our previous models.

First, the 6623. This flywheel is basically a billet replacement for the stock flywheel and plastic fins. The keyway is in the stock position and it is designed to use the stock pull starter. $195.00

The 6622 also has ARC's steel adjustable timing hub and a bolted-on ring gear made of super strong 7075 billet aluminum for the on-board electric start. Some adaptation is required if you also want to be able to use the pull starter. $250.00

Cutting EL Tires

2008-06-30T11:59:00.002-04:00

http://video.google.com/videoplay?docid=2823905883109981466&hl=en

More like grinding than cutting. I can take a new EL tire down to "low dots" in 8 minutes with this machine. I sell a new set of ground tires mounted on Douglas Q+ wheels for $380 plus shipping (and tax in GA). If you bring me your tires already mounted, I charge $20 per tire to grind them. Prepped tires CANNOT be ground. 800-521-3560

BSP Valve Springs (when to change and why...or why not)

2008-06-26T08:18:00.004-04:00

I have about 150 new springs in stock. I have checked about 50 of them in many ways. They are all so close to one another that I quit testing. I compressed a brand new spring to its solid height and it lost tension to the point that it was no longer better than a spring with 14 races on it. I stretched a spring, and it went up in tension, but after compressing it at full cam lift, it was right back to where an untouched spring was. All the fresh springs measured 10.8 lbs at .850”. My scale is only accurate to .2 lbs, but my measurements are accurate to .001”
So here’s the kicker. If you are running the stock air box and filter and the stock muffler, heavy springs are actually bad because the engine makes more power and is faster at about 5200 RPM, which is well below the 5800-5900 RPM valve float RPM. Added tension is just a waste of energy. With the little header and muffler along with an air filter adapter and bigger jet, the power band moves up slightly in the RPM range, but still not enough to turn the engine to the point of floating valves. So basically, if the intake and exhaust is left stock, worn out springs are better, and with an aftermarket intake and exhaust you will want to freshen your springs after a few races. Changing springs is very simple and can be done with your bare hands without removing the head from the engine. I'll do a picture story on that and post it here this weekend.

Parts for the 6.5 HP OHV Engines

2008-06-11T08:15:00.007-04:00

ARC now has inventory of new parts for the Yellow OHV 6.5 Horsepower BSP engines and the Blue 6.5 HP engines.

We also carry high performance parts for these engines including stainless valves, HP springs, billet aluminum spring retainers, billet rods, billet flywheels, cams etc.

We are fully engaged in loading all these parts onto our webstore and expect to have all out clone related parts online before the end of February.

Pulsing the Fuel Pump from the Rocker Cover

2008-06-09T18:43:00.006-04:00

I drilled a hole to insert a 1/8" pipe nipple into the rocker cover. The hole is below the baffle plate in the rocker cover so it is pulsing directly from the rocker chamber. The red vent tube is above the baffle plate. I have raced this a couple times now and it works very well.

Box Stock Build Video

2008-05-01T12:00:00.002-04:00

This is an instructional video (Updated 1/4/2009) to help kart racers prepare their 6.5 HP OHV clone or BSP engines to compete under AKRA's 2010 Box Stock rules.

UPDATE 4/15/2010 We have come a long way with these engines since this video (shot 1/4/09) and the original YouTube build videos (shot 8/4/08) http://www.youtube.com/watch?v=FTNbDvfIHoo
My new videos are all posted on Ustream at http://www.ustream.tv/channel/karttrax

Things change (usually for the better) as time goes by. There is good info in the older videos, but any information in newer posts and videos supersedes the older stuff.

This video and the information on this blog are free for your consideration. Use it at your own risk. Neither ARC, nor I will be held responsible for your engine's failure. Parts break in racing engines. It does not happen often with these engines, but anything made by man is fallible.

Superbox build

2008-04-20T17:58:00.005-04:00

CLICK ON THE PICTURE TO ENLARGE IT

This dyno run was with just about everything done to the engine under AKRA's present superbox rules that can be done with bolt on, or swap out parts only. The only modifications made that can't be undone are boring of the stock carb to .623, and grinding the throttle shaft. This engine has a new cam in it from Dyno Cams.

To put this in perspective, this engine is making about half a horsepower more than a "stock" Animal on my dyno. Total cost in parts for the race-ready engine is about $450 (racer price). The engine has low vibration and runs very smoothly.

NO porting has been done. I have done a lot of swapping and measuring. I have found a very good valve train setup that yields 21lbs at the seat and 56lbs nose presure. I have turned the engine to over 8000 RPM, and I have held it at 5000RPM for 10 minutes. There are some minor things I need to do, and I have some theories on the carb that should pick up the bottom end without killing the top end.

New Cranks...Lower Cost

2008-04-02T14:29:00.002-04:00

Our stock-stroke and +.200 stroker flathead cranks are now made of a less expensive, hardened chromolly steel. The stock stroke crank is also used as a stroker crank in the Animal.

The new stock-stroke crank is part number 6580-C and the +.200 in part number 6584-C

The new cranks are $299.

Header Comparison, Stock vs Small Muffled Header

2008-03-25T18:48:00.005-04:00

CLICK ON THE PICTURES FOR A LARGER VIEW

First, I need to explain why the Box Stock dyno numbers are higher now than they were originally. Since my original dyno pull, I have removed the internal governor gear and changed to a 5w15 synthetic racing oil from Castrol GTX 10w30 conventional oil. The racing oil also has "Chili Oil" added, which is a friction reducing additive. And finally, the engine saw a lot of use this weekend that seems to have finished "breaking it in."

The only modifications made to this engine were the removal of the governor and low oil sensor.

In the pictures, the column titled "EGT #1" is Cylinder Head Temp the column titled "EGT #2" is Exhaust Gas Temp.

This is the new Dyno run with the stock muffler.

This is the Dyno run with the small muffled header. The engine makes higher peak HP at a slightly higher RPM, and the HP is higher all accross the RPM range with the small muffled header. Peak HP is 1 HP more than what was produced with the stock muffler.

The valves are begining to float noticably at 5800 RPM and appear to float sooner with the small muffled header.

Flywheel Comparison

2008-03-11T19:45:00.011-04:00

CLICK ON THE PICTURES FOR A LARGER VIEW
This is a back-to-back dyno comparison of the yellow engine using the stock, and then the billet flywheel. This is the same engine from the dyno run I posted the other day. I have since put about 40 laps on it and changed the oil, installed the all steel cam and set the valve lash. This engine still has the stock air box with the paper air filter and stock muffler. I decided to start recording at 2500 RPM to illustrate the "torquiness" of this engine. I used 87 octane pump gas and 10w30 Alisyn synthetic racing oil.

This first dyno run is with the stock flywheel and is very similar to the run from the other day.

For the second dyno run, the only change I made was switching to the ARC 6619 billet flywheel.

The engine produced more horsepower with the billet flywheel across the entire RPM range. Peak HP is about 1/2 HP greater at 4200 RPM, and the engine is producing 1 HP more at 5600 RPM with the billet flywheel.

Box Stock Dyno Numbers

2008-03-08T21:07:00.004-05:00

Results of dyno testing the Box Stock Engine. The only modification done was removal of the external portion of the govenor. 87 Octane pump gas and Castrol GTX 10w30 conventional (non-synthetic) oil was used.
Notice how the HP numbers begin to decline rapidly at about 5400 RPM. This is due to the restrictive muffler and the weak valve springs beginning to allow valve float; good built-in govenors.

ARC flathead billet flywheel for PVL

2008-02-05T15:06:00.001-05:00

ARC now has a billet flywheel for the flathead that will allow you to use the new PVL ignition from B&S. We have seen substantial gains with this coil and flywheel over the standard (old) coil and ignition.

The new flywheel (#6617) weighs 3.85lbs. It has adjustable timing and is SFI certified.

Although this new flywheel has a larger diameter than a 3hp flywheel, the rim weight of the new flywheel is considerably lighter than the 3hp models. This means that acceleration with the new flywheel would be about the same as a 3hp model. BUT, the PVL ignition used by the new flywheel will give you gains beyond what you could ever get with the 3hp models with standard coils.

The reason this flywheel must have a larger diameter than a 3hp flywheel is because the PVL coil is designed for a specific diameter and appears to be sensitive to any deviation from that diameter.

Tecumseh OH Billet rod from ARC

2008-02-05T14:40:00.001-05:00

ARC now has a stock replacement billet rod for the Tecumseh OHH 5-6HP engine.

Part #6282 3.484" (stock length). $59.95 MSRP

It does not use bearing inserts.

PVL Ignition on a 305

2008-02-05T14:37:00.001-05:00

Hey guys, just wanted to pass along that Randy is working on coil brackets that will allow the use of the PVL coil and one of our new billet flywheels for the PVL on a 305. One of the brackets will be for a stock crank setup and the other will be for a stroker setup.

We have not tested this on the 305 yet, however, we found significant gains on 330' Outlaw Jr Dragster engines and on Animal engines over what we were able to produce with our original billet flywheels and standard coils. In order to get the greatest improvement, we had to richen up the fuel/air mixture and reduce timing from the settings normally used with the standard setup. On the Drag engine, we ended up with a longer header pipe and actually needed to put on a bigger carb because the engine wanted more fuel than the smaller carb could deliver. This testing was done at Roy Whaley's shop on one of his highest horsepower engines. The HP increase was anywhere from 1/2 to 2 HP and the fall off on top end was not as steep as with the standard coil.

ARC rod for the stock 305 crank.

2008-02-05T14:14:00.001-05:00

P/N 6231 - 4.335" Uses the stock crank and an JE "EXF4500" piston with a .490 wrist pin.

This rod will give you the same compression height as our P/N 6235 stroker rod for the same piston does with our P/N 6585 stroker crank.

1.2 ratio rockers for GX200 and Clone

2008-02-05T14:09:00.001-05:00

These are the stock rockers for the Yamaha YF200 engine and they work fine in the GX200 or Clone. You will have to either make a new pushrod guide plate, or adapt the one you have.

part# F21-408-00

.032 Copper Head Gaskets for GX200

2008-02-05T14:04:00.003-05:00

I have had these for a while and never have done a good job getting the word out.

P/N FG9591 Flatout .032" rubber coated copper $12.46ea.

GX120 ARC Billet Rod

2008-02-05T14:04:00.001-05:00

We have a new stock length billet rod for the Honda GX120. P/N 6273
It does not use bearing inserts and weighs 28 grams less than the stock rod.

You must remove the low oil sensor unit and it is probably a good idea to check your crank and have it polished prior to racing. The crank we had was a little rough.

A new big valve option for the GX200 or Clone

2008-02-05T14:03:00.001-05:00

I just got in the new Burris Gen III valve kit for the Yamaha and it works wonderfully in the GX200. We need to substitute a few of the parts with some others.

Here is what you need for this setup:
2 F21-408-00 rocker arms $9 ea
2 F21-405-11 intake springs $7.50 ea - yields approx 19lbs at the seat with plenty of room for shims
2 F21-417-00 lash caps $4 ea
2 F21-406-20 spring retainers $7 ea
2 F21-407-20 retainer lock set $7 ea
1 F21-402-25 stainless intake valve $31
1 F21-403-20 stainless exhaust valve $31

We carry .015" .030" and .060" shims @ $1.50 ea

I recommend the push rods from the clone engine, however, I do not have them yet.

The intake valve is 1.070" (.072" larger than stock) and you will want to either install or have installed a new large inside diameter intake seat, (p/n 6148Y $8) or have a 60° cut on the existing seat to open it up to take advantage of the larger valve.

You will have to open up the slots in the push rod guide plate on the GX200 if you go with the clone pushrods. If you are hopping up a clone, you may need to fabricate a new push rod guide plate.

This setup gives you a large intake valve, approx 30% more valve lift, and as much spring pressure potential as you could possibly need. You need to use a billet flywheel and a billet rod with this as well. I think the long rod and a JE EXF4500-120 piston would be the best setup there. I also think the PVL ignition, along with the matching ARC flywheel will be the hot ticket if you are going with methanol. I personally suggest calling EC Distributing for your carb and billet intake. I have a few intakes and some gas carbs. But when I need a rockin carb for methanol, I call Carroll Ford at EC.

With this setup, you will be taxing the limits of strength on both the crank and the block. Where the line will be will depend on a lot of things, but if you can't stomach blowing up a motor, you might want to let some of us who live for that sort of thing find the weaknesses and come up with solutions.

Using a Long Rod in an OHV Kart Engine

2008-02-05T14:00:00.001-05:00

This Article is specific to the Honda GX200, but the same clearance principles apply to just about any engine.

Since wiseco is eliminating their kart piston production, we want to focus on the use of J&E pistons in our instructions in order to avoid confusion.

The long rod is 3.707" long (+.404"). With a 3.707" rod, ANY piston that will fit the bore of your engine that can be cut to a .520" compression height will give you the same overall length as the stock length rod (3.303") with the stock piston (.924" comp hgt).

We do not have undersized bearings for our Honda rods at this time. If you are running a babbited bearing, your crank wear will be almost nil. That Honda crank is very good.

Some of you guys are talking about decking your block and/or shaving the head. That all ties together with the required compression height of your piston.

Two rules:
1. The minimum distance between the bottom of the head and the top of the piston should be .030". (I'm not going to get into domed piston theory here because it is not applicable here.)
2. The minimum distance at the closest point between the valve head and the piston during operation .090"

Every block is a little different. Assume for a second that the piston and rod combinations are fixed at 4.227" (stock length). Let's say that your gasket is .010" thick. Your piston would need to be .020" in the hole based on the .030" rule. In order to maximize compression, after decking your block, you want to shave the head until the valve head is as close to .090" from the piston when they are closest using the cam you intend to run. That's the very best you can do without a domed piston with valve cutouts. All these things have to be measured by mocking up each engine.

OK, now throw in the fact that the aftermarket pistons will need to be cut down to get them to a .520" compression height to achieve the 4.227" stock length. There's nothing that says you must cut that much off the piston other than making certain that the .090" valve rule is respected.

Since a JE EXF4500-120 piston is only .004" larger than a stock bore piston, and it has a .610 compression height than can be cut down, lets use it.

note: FYI, the JE EXF4500-140 and wiseco 1982p140 pistons, which are .024" over stock bore, have a .620 comp hgt and can be cut down to .520" but the wiseco 1990p120 piston has a .565" comp hgt and may not be able to be cut down to .520". If you follow that, you will understand why the JE EXF4500-120 is the best first choice.

Back to our example above. We said the piston would have to be .020" in the hole. If you mock up your engine with a stock rod and a stock piston and the piston is actually .030" in the hole, then you have two options with the long rod and the EXF4500-120 piston. You could cut .090" off the top of the piston to take it from a .610" comp hgt down to a .520" comp hgt and also take .010" off the deck of the block, or you could just take .080" off the piston and leave the deck alone. In either case, you are moving the piston .010" up in the hole and .010" closer to the valves, so keep that in mind because of rule 2 above.

This long rod is designed to clear the underside of the JE piston without modification to the piston or the rod.

Hunter or I can help you with all this in order to cut the the piston for you. We will need to know how deep your piston is in the hole with the stock setup AFTER any decking you are going to do. We can only assume that you have checked your valve clearance.

Seriously, if you are building an engine, you need to grasp this stuff in order to build the most performance that won't grenade due to lack of proper attention to known constraints.

One last rule of thumb: The piston dome should not be less than .100" thick in the center.

New ECONOMY Flathead Billet Flywheel from ARC

2008-02-05T10:01:00.000-05:00

We have a new SFI certified non-adjustable billet flywheel for the flathead. This flywheel is stock diameter, weighs 4.05lbs, and has the keyway set at 30°.

The only difference between this flywheel and our Limited Mod adjustable flywheel is that this one does not have the steel adjustable timing hub.

Part #6620 introductory racer price $125.00
We made the flywheel that best fits ARC's capabilities. It's the best piece we could make with focus on affordability and maintaining our SFI certification. That's the best we can do for the racer. The design allows you to start your engine with either an electric starter OR the Briggs BS555165 manual pull starter.

ARC billet rods for the Vanguard / Mitsubishi OHV 6HP

2008-02-05T09:24:00.000-05:00

We have two new billet rods for the Briggs and Stratton Vanguard OHV 6HP

#6264 Stock Length 3.465", uses stock piston $83.95 MSRP

#6263 Long rod 3.850", uses JE piston #EXF4500-120 with approx. .090" cut off the top. It is .385" longer than stock. $83.95 MSRP

Both of these rods use the same bearing inserts as the Honda GX200 (and clone) engines. By increasing the number of rods that use this bearing, we hope to be able to justify undersized bearings.

Does ARC make Custom Rods?

2008-02-05T09:18:00.000-05:00

Quoted from http://karting.4cycle.com/showthread.php?t=167398:

Q

How expensive is it to have a rod built to a custom length?

A

That depends on the length, and we have to make a minimum of 3 rods. A bore diameter change at either end is $750 (for each end) unless it matches up with a bore of one of our existing rods so we can borrow existing tooling. A length change could be as much as $2000, unless it is only a slight center to center change that will fit within an existing rod profile. The same profile allows the use of existing jaws.
So, for the first 3 special rods, $600-$3500 (for all 3) depending on those factors. Additional rods made in the same run will be about $100 each depending on how many you get. There are other factors that could make it more, or less expensive, such as material cost and availability.

On Rod Bolts, By Mike Gifford

2005-04-04T08:20:00.000-04:00

My name is Mike Gifford; I'm "Outrider" in the 4Cycle.com forums, the guy that commented on how happy I was to see a fastener tightening procedure that made allowances for the differences in friction coefficient (and hence applied torque required) when different thread lubes are used on threaded fasteners. At the time, I promised you that I would eventually send you some comments on fasteners and tightening procedures.
By way of background, I started my engineering career with a BS degree in Engineering, an Ensign's commission in the Naval reserve, and an Unlimited Horsepower US Coast Guard 3rd Engineer's License for both Steam and Diesel ships. After several years as a sea-going Marine Engineer, I came ashore in 1970 and eventually went to work for the Navy. I ended up as an engineer in the Submarine Fluid Systems Division, and spent the better part of the next thirty years in various Engineering and Naval Architect billets in the Naval Sea Systems Command, all in the submarine community. Got to ride/play with things most people only see in National Geographic specials and on the History Channel, and got paid for it. And got to retire when I was 55.
Submarines have thousands of bolted joints, many in critical applications, which, in the end, accidentally caused me to build a small empire within the Navy's engineering community as a fastener expert. Amazing how a collateral duty (that's all it ever was) gets to be a big deal.

In the early 1970s, the Navy's submarine community realized that they had a bunch of bolting problems; both with fastener selection and joint assembly, and by 1978 published a Submarine Fastener Manual. In 1981 I switched jobs and, as part of my new job's duties, inherited responsibility for that manual; after that, wherever I went in the submarine community, the job description for my new position would be rewritten to include the Submarine Fastener Manual and all submarine fastener problems as a collateral duty. As one who had been assembling motorcycle and automobile engines since he was 12, and new how to use a torque wrench, I thought I had this one wired. Within 3 days of inheriting the Fastener Manual I discovered that I about had the tip of the iceberg wired, and embarked on a very steep learning curve for the next two months. The learning hasn't stopped to this day, but the curve is rarely that steep any more. My specialty was "in service" engineering - how to select a fastener that would live for a specific application, installation procedures, including procedures for tightening with a torque wrench, use of angular turn, and use of ultrasonic direct stress measurement; review of failed fastener analysis reports and developing solutions for preventing those failures in the future. The less publicly visible (but probably more important) section handled fastener materials, manufacturing processes and QA/QC testing of materials and finished products, and contributed to my ongoing education on a regular basis. So that's how I got to be a fastener geek/goon.

Random comments, in no particular order of importance:

1. While there are many materials used for bolts, cap screws, machine screws and nuts, where there are not problems with corrosive environments or other special considerations, selecting from among the various steel alloys used for fasteners is a hard act to top.

2. In the drive to reduce space and weight, ever-higher strength alloys are considered. This is a good thing if not carried to extremes, but people need to remember that high strength is no good without toughness. Just because a fastener is strong doesn't mean it is tough - VERY high strength fasteners (250ksi - 270ksi yield, as found in some heat treats of some of the Nickel/Cobalt alloys) tend to be brittle and not respond well when subjected to high shock loads. Since they don't stretch much, they break, where a tougher (though less high strength) alloy will just stretch. Of course, the tougher alloy would usually have to be a larger diameter or use more fasteners in the joint; everything is a compromise in the fastener world.

3. Concerning toughness and resistance to high shock, there is an all to often ignored quality buried in fastener material chems and physicals called "Percent Elongation" which makes screening for toughness relatively easy. The Navy's big hurdle is passing tests for resistance to "Hi Shock and Undex" ("Undex" is short for UNDerwater EXplosion). The Navy flatly refuses to allow components (including the fasteners holding things together) in critical applications to use materials with a percent elongation less than 10%, and will only VERY rarely allow materials with a percent elongation less than 10% in a non-critical application by approval of an exemption specific to that component for a specific service on a specific class of ships (we're speaking combatants here; noncombatant ships are allowed a little more leeway in their design). In general, to meet hi shock and Undex requirements, materials with a percent elongation of 15% or more should be chosen, over 18% is better, and, as heat treating processes for metallic alloys in production quantities has improved over the last 20 -30 years, many fastener alloys that were in the 15% - 18% range can now be reliably produced in the 20% - 25% elongation range, which is great for toughness. Fortunately, by the nature of the beast and the general conservatism of mechanical joint designs used in shipbuilding, any fastener material with a percent elongation of over 10% will generally pass hi-shock/Undex in a properly designed bolted joint. To protect its flanks, the Department of Defense has some specifications that it piggybacks onto commercial specs (MIL-DTL-1222, for instance) to get what they need in this respect, so an ASTM A574 4340 socket head cap screw for a critical application would be ordered with a minimum percent elongation over 10%, which is higher than the minimum demanded for 4340 socket head cap screws in A574. And many engine building applications don't have the hi-shock loads present in Undex testing and can benefit from really high strength fasteners, even if their percent elongation is less than 10%, but you do have to match the alloy chosen to its shock environment carefully.

4. Once the user the user settles on the basic fastener configuration (hex head cap screw, socket head, 12 point, etc.) and the correct material, the most important things (more important than material and basic configuration, unless grave errors are made in selecting those two items) are the geometry of the fillet radius where the unthreaded shank joins the head and the transition from the threaded portion to the unthreaded shank of the fastener. Errors in design or execution in either of these two areas can result in fastener failure where it would not otherwise occur. To eliminate problems in the threaded to unthreaded shank portion, use of rolled threads is usually sufficient. For the shank to head transition, the proper fillet radius needs to be specified, and adherence to that specification needs to be checked religiously as part of the QA program.

5. When doing qualification testing or random sample receipt inspection of fastener lots, the most effective single physical test (after a good visual inspection and dimensional checks) to verify the quality of a finished fastener (including the items in 4. above) is a wedge tensile test per ASTM F606. The beauty of the wedge tensile test is that it is done on a finished fastener, not a machined tensile test specimen, so it picks up both material problems and manufacturing defects like an inadequate fillet radius. Generally, if you purchase fasteners from an outside source, they will state what specifications are used for manufacture and random sample visual inspection and dimensional checks are sufficient. Cash flow permitting, it's nice to send a few to a lab once in awhile for a wedge tensile test by an independent lab - I was spoiled; any Naval Shipyard had a lab with lots of neat machines, including a tensile test machine.

6. With regard specifically to rod bearing cap screws for ARC connecting rods, my inspection of a limited number of these fasteners (two rods from my engine builder's stock) left me impressed. Their high quality was obvious, as was correct design and execution of the fillet radius and the thread transition (to the extent that this can be determined by a visual inspection, but I'm willing to bet that they would pass a wedge tensile test without breathing too hard), but more interesting was an extra little design feature, a reduced diameter section in the unthreaded shank of each cap screw. That little feature actually improves resistance to shock and greatly improves performance in hi-shock situations. Basically, it makes the fastener a better spring, mitigating shock damage by increasing fastener toughness with a mechanical trick, rather than exotic metallurgy. As an example of what this feature can do, the Navy has subjected a group of fasteners (studs in this case) to a shock load that would make them fail; the average stretch was 1/16" before they broke. Repeating the test with studs identical except for a slightly reduced diameter in the unthreaded section, the fasteners actually stretched an average of 3/16" prior to failure. When not carried to extremes, that little feature is an excellent way to improve high shock performance, and it doesn't take much reduction to collect that benefit; obviously, too great a reduction in diameter in the unthreaded shank will reduce ultimate strength more than it benefits shock resistance, but it is usually possible to strike an effective balance without causing problems if the fastener design isn't right on the edge of failure due to the in service load profile to begin with.

7. Excerpts from a Navy training lecture - "What your mother and the professors didn't teach you"

A. Preload range of bolted joints assembled with a torque wrench:

Most people see a torque specification for the threaded fasteners in a joint assembly and think that (1), the desired preload is achieved with great precision, and (2) that the fastener-to-fastener preload variation within the joint is small. Neither of these impressions is correct. On the best of days, the fastener-to-fastener preload variation is about 35%, and often more. It is not unusual to see the largest preload measured in the bolt circle twice that of the smallest in joints assembled with a torque wrench by an inexperienced mechanic without benefit of a proper installation process. Although other standards have been (and when there is a specific reason, still are) used, most bolted joints found on submarines (that require use of a torque wrench for assembly) have a preload established at 2/3 of yield of the weakest element of the joint (150% of yield in the case of bearing stress), and, ideally, the limit will be reached as tensile stress in the bolt or stud.

So you have a torque from a drawing, Maintenance Standard, tech manual or whatever, based on, say, 2/3 of yield. When the mechanic is done assembling the joint, all the bolts in the bolt circle would have (theoretically) a tensile load of 2/3 of yield, because the torque was chosen to give that result. Unfortunately, there is a significant fastener-to-fastener variation in friction coefficient, AND a significant fastener-to-fastener variation in short term preload loss (the relaxation that occurs in the first 2 to 10 minutes after the wrench is removed from each fastener in the bolt circle for the last time). And a few other things (all told, about 76 different things, according to the Air Force, which did an excellent study on the subject, like prying loads and cross talk. The result is that all we know for sure is that each fastener in the bolt circle, having been tightened to a mean torque mathematically equivalent to a mean preload of 67% of yield, has an actual preload of somewhere between 40% and 90% of yield. It sounds crude, but it's close enough, even for hull integrity/high shock/UNDEX/hazardous fluid, etc, services. The distribution of this preload variation is more or less a bell shaped curve in a statistically valid sample.

B. The value of process instructions:

The real case is not quite as bad as the above makes it look, as the methods incorporated into Navy/Navy approved process instructions are designed to reduce this preload spread. The reality is that the multiple passes, check passes, etc, of Navy process instructions skew the curve. The top value (90% of yield) doesn't change, but the number of fasteners below 67% is significantly reduced, and the amount by which they are under 67% of yield is also reduced, while the number between 67% and 90% is increased. Since the best defense against long term preload loss is high initial preloads and minimization of fastener to fastener preload variation, the value of good processes and training in those processes is once again proven.

C. Good shop practice and precision:

As far as fastener to fastener preload variation is concerned, the variation for fasteners in a joint tightened without a torque wrench, but in stages and with check passes, is 5% to 10% more than the variation with a torque wrench, on the average. In reality, other than being cheap to use, the torque wrench only offers 3 advantages:

1. It assures adherence to a specified mean torque, which in many joints is not a particularly significant item, except for record purposes, or where minimizing the chance of exceeding the yield strength of the material or the threshold stress level of an H2 embrittlement prone material is important.

2. It results in slightly less preload variation than the use of "good shop practice" and a box end, open end or socket wrench, in the hands of an experienced technician.

3. It offers visual proof to witnesses that each fastener in the bolt circle has been properly tightened, needed for certification records for "critical joints".

For what it's worth, the most accurate method of tightening the fasteners in a bolted joint without resort to expensive ultrasonic measuring devices, strain gauge equipped bolts or other cost increasing approaches is angular turn of the nut. The fastener to fastener preload variation runs about 15%, much better than a torque wrench can ever hope for.

When fasteners are overtorqued severely during initial installation but survive the procedure without failure, the joint is generally OK for service without further action. Various embedment phenomena and other short-term preload losses will reduce the stresses to a high but acceptable level. The exception is where the fasteners are made of materials prone to hydrogen embrittlement. They may settle out, after short-term preload loss, at a level in excess of their threshold stress level, leaving a high probability of brittle failure in the future. Resolution where H2 embrittlement prone materials are involved should always favor loosening and re-torquing, one fastener at a time, to the correct value (Note to Tom: Many bolted joints on Navy ships require hydrostatic testing for verification. If the joint integrity is violated by loosening the fasteners, an expensive retest is required. By common sense and resulting executive fiat, the Navy does NOT regard the integrity of the joint as violated if the fasteners are loosened and re-tightened one at a time, saving the expense of retesting, hence the importance of "...one fastener at a time"). If discovery is after the joint is buried by interferences and cost is too great, use of Level I certs may allow acceptance based on stresses adjusted for the actual yield rather than the min spec numbers usually used in design calculations and by PC Bolts. Fasteners of materials such as Grade 5 steel and other materials not prone to H2 embrittlement may be left as is and torqued correctly at the next disassembly and re-assembly of the joint unless the activity is having a lot of such errors, in which case remedial retorquing is necessary to get production's attention.

G. Notes on choosing thread lubricants:

2. Once in awhile the subject of the range of friction coefficients that will be exhibited by a thread lubricant will come up. When discussing this subject, insist that the range be tied to a specific material (nut and bolt or stud) combination. The reason for this is that the same lubricant often has both a different mean friction coefficient and different extremes (and can have the same mean friction coefficient, but different extremes, the high and low values that establish the range) when you compare the mean and extremes for different combinations; alloy steel and alloy steel, CRES and CRES, Monel and Monel and KMonel with a monel nut, for instance. The extremes for each material combination establish the range FOR THAT COMBINATION. Taking the high for the combination that has the highest extreme and the low for the combination that has the lowest extreme, a method that will quite often be attempted by your Nuclear counterparts if you don't call them on it, doesn't give the range, it gives a number useless in calculations and of little interest in intelligent discussions.

8. Notes on tightening procedures (the following is a slightly edited excerpt from the Navy's Submarine Fastener Manual, from the sections that are the basis for development of local activity's process instructions and instruction packages for individual work packages, where such detail is necessary for a specific work package. As you can see, the basic approach is relatively simple and grounded in common sense. It also would pass as the generic basis for ARC's specific procedures):

Before tightening any fasteners, the following should be performed:
a. Examine fasteners for compliance with marking requirements.
b. Examine the internal and external threads for burrs, nicks, metallic slivers, etc., that could cause jamming or excessive resistance to tightening. Remove or correct as necessary.
c. Ensure the threads and mating bearing surfaces are clean and free of rust, chips, or other foreign matter.
d. Ensure the nut (or cap screw) seating surface is flat and contacts the mating surface all around.
e. Lightly lubricate the threads and bearing surface with the specified lubricant and remove excess lubricant to permit air to escape from under the nut (or head of the cap screw). Flange spot facing should also be lubricated.
f. If using torque measurement method, ensure the torque wrench has a current calibration sticker. Select a torque wrench such that the required torque is between 20% and 90% of the full-scale range of the torque wrench selected.

FASTENER TIGHTENING PROCEDURES. The following procedures are applicable to nuts, through bolts, studs, cap screws, and set-studs used on flat-face and raised-face flanges:
a. Prior to applying final torque, perform the prerequisites described in steps a through f above.
b. Assure proper alignment of the mating components.
c. Where the application requires O-rings or gaskets, ensure the O-ring or gasket is in its proper position. Make up the joint evenly by tightening diametrically opposite fasteners until the mating components contact each other. This will normally be accompanied by a noticeable increase in torque when metal-to-metal contact is made. Check all fasteners to ensure that no fasteners are loose. Continue to tighten fasteners sequentially. Apply approximately ten percent of the specified torque to ensure solid part contact. Finish torquing the joint in 25 percent increments of the specified torque.
d. For determining torque values used in this procedure, refer to paragraph 5-5, use Appendix E (PC Bolts), or seek guidance from your activity's Design Division.
e. When tightening nuts in set stud and nut type joints, check stud rotation by marking with a felt-tip marker on the nut end of each stud in a direction toward the center of the flange. Check the mark on each stud after tightening to ensure the stud did not rotate.
f. After completion of the last tightening pass, wait a minimum of 2 minutes, and execute a check pass or passes until the joint holds the specified torque setting. This minimizes the effects of short-term preload loss and helps minimize fastener-to-fastener preload variation.

9. Where hydrogen embrittlement is mentioned above, it shouldn't be a problem in the environment of a rod bearing cap screw, since you need high stress (above the material's threshold stress level) in the fastener, a source of free hydrogen and an electrolyte, and an electrical potential, like screwing a Kmonel stud into an HY-80 steel pressure hull, or a steel cap screw into an aluminum rod - the whole world is a battery waiting to happen once you introduce dissimilar metals. High strength steels (140 ksi yield and above for purposes of H2 embrittlement discussions) are subject to H2 embrittlement and can be assigned a threshold stress level of 80% of yield (threshold stress level is a bit of a moving target, but 80% of yield is a good working value for high strength steels), but for embrittlement to be a problem, you have to have ALL the factors, not unlikely in the marine environment, but HIGHLY unlikely inside an engine, even if the target mean preload is 90% - 100% of yield for the rod bearing cap screws.

10. Where PC Bolts is referred to above, it is a relatively simple to use computer program developed by the Navy for calculating fastener torques for bolted joints. I can send you a copy if you're interested in playing with it - it covers through bolted joints, cap screws threaded into blind holes, and set stud and nut type joints. The present version is a pleasant little calculating machine in 16 bit Dos code, so old it lacks mouse support, but it's lean, mean and gives you torque, preload and a large collection of joint component stresses. Or you can input a torque and get preload and the stresses, or input a desired preload and get the necessary mean torque and stresses. The Navy hands it out for free to anyone that wants it. My one mule consulting outfit heads the Beta test program for the new 32 bit Windows version, which we will have out soon and which also will be given away free to anyone that wants it, once it's ready to release into the wild. As a Navy employee I headed Beta testing for the three previous versions, so PC bolts is sort of the crown jewel of the contributions I've been able to make to solving fastener problems; that, and a whole bunch of friction coefficient testing that went into the lubricant library of PC Bolts, and which led me to take note of your rod installation instruction.

11. Oh yeah, one other little item; all of the above discussions assume that when the designer chose the fastener size and alloy and the preload we are going to apply to the fastener, he/she had a reasonably good idea of what the worst case in service load will be and chose the preload to be well above that load after short term preload loss and a reasonable profile for long term preload loss. If we blew any portion of that little set of choices, we have the potential for cyclic load reversal and good old fatigue failure. Short term preload loss can run anywhere from 5% to 40%, though proper tightening procedures will make it unlikely that you will ever see the latter figure. Our preferred approach is to take the max in service load and select a preload 4 times that amount, so that you can lose 50% of your initial assembly preload to any combination of short and long term preload loss and still have twice the preload needed to do the job - crude, but it works. Most bolted joints work well because their design is conservative (if nobody goofed), and hence they are very forgiving of minor errors, abuse and neglect. Of course, the more refined your design assumptions are from a standpoint of test results or other prior experience with a specific application on which to base your decisions, the closer you can cut it if space or weight considerations intrude, without putting the joint's integrity in danger. In combatant aircraft design, there are bolted joints that are subject to fatigue failure in order to reduce size to fit in the space available. With fatigue life to failure in a cyclic range that corresponds to 12 to 18 months of service, the aircraft maintenance plan calls for automatic replacement every 6 months. That's a valid solution for a fighter plane, but probably won't hack it for a passenger car.

12. I have repeatedly used the terms hi-shock and Undex in the discussions above. To give you an idea of the magnitude of the forces we're dealing with when Hi shock and explosion testing are invoked, civil engineering design for earthquake involves designing for accelerations primarily in the 9G to 11G range. Hi shock and Undex deal with G forces in the 450G range, give or take, and greater.

Are you Unbalanced?

2003-10-29T08:22:00.000-05:00

By Tom Cole

Several years ago when we were developing our crankcase ventilation system for the Tecumseh Star engine, I got some seat-of -the-pants experience with the value and need of crankshaft balancing. I was accustomed to driving a 3” bore, 3” stroke test engine, which had one of our billet crankshafts in it. The 3x3 crank had been balanced, and ran very smooth considering it was producing about twice as much horsepower as the Star. The Star’s crank/rod/piston setup had not been balanced, and the difference took me by surprise. As I made 8000 rpm, my vision was so blurred from the engine’s vibration that I had to slow down to see the turn. My teeth and ribs felt like they were banging together and after my 15 lap stint at this ¼ mile asphalt oval, I was not interested in driving any more that day. My body was directly reporting to me the increased pain and fatigue that an unbalanced crankshaft can do to an engine and driver.
Clarence Clark is a friend of mine and he is what I would call an engine-building guru. For many years, Clarence’s company rebuilt the engines for the world’s largest fleet of racecars, the United Parcel Service. He has since traveled the country doing seminars for rebuilding supply companies like Goodson and Cobra Products. When I told Clarence about my experience, he went over to his tool box and produced a metal “H” which was made out of five, six inch long 3/8” metal pipes and two 3/8” pipe “T’s”. He handed me this contraption and told me to gently hold the cross pipe in one hand like an axle and spin it. Everything was fairly in balance and it spun easily making five or six revolutions. He then removed one of the four, six-inch uprights from the “H” and said “now it’s out of balance, spin it again.” I did and it only made one revolution! When I tried to spin it real hard, it only made two revolutions. This was an example of the need of both Force and Couple or “Dual Plane” balancing of a crankshaft. He told me one of the most interesting things about an out-of-balance crank or cam is that this tendency to stop (or inertia) increases with RPM so it requires more and more horsepower to obtain the same RPM as a balanced setup! It is hard to believe that we spend so much time and money on carburetors, valves, porting, flow and displacement and many of us ignore or are unaware of such a power robbing aspect of an engine.
Force and Couple balancing are technical terms used that really just mean top-to-bottom and side-to-side balance and are commonly referred to as “Dual Plane Balancing.” They are easily illustrated with a little history in tire balancing. Many years ago, when car tires were balanced, the rim and tire assembly was mounted on a shaft and then placed on a frame with the shaft resting in a ball bearing V fixture. The tire assembly would then rotate around until the heavy part came to rest at 6 o’clock. A wheel weight was then placed at 12 o’clock on one side of the tire. You kept adjusting this weight until the tire would not move regardless of how you repositioned it in the V fixture. This process is called, Static, or Force balancing and it is the method that is used on most kart and Jr. Dragster wheels today. Later, an improvement was made in this process by splitting the weight and putting half on the inside of the rim and half on the outside. This was the first form of Couple balancing in the tire industry. As years went by the advent of much wider tires came into being, so the need for more accurate Couple balancing increased because the part of the tire that was out of balance was often further from the centerline of the tire. And since one side of the tire could weigh more than the other, it became necessary to be more precise than to just split the weight in half to achieve optimum balance. We now have electronic tire balancers that spin the tire and wheel and calculate the amount of weight needed to Force balance. Then it calculates what amount goes on the inside of the rim and what goes on the outside. This is Dual Plane balancing of a tire.
The crankshaft of an engine has counterweights to dynamically offset the effect that the movement of the reciprocating mass has on the rotating mass of the crankshaft. The reciprocating mass is a percentage of the total mass of the top half of the connecting rod, the piston, wristpin, rings and circlips. The percentage used comes from a chart, which is calculated from expected RPM and stroke length. The rotating mass is the total mass of the bottom half of the connecting rod, the rod bolts, washers and bearings. To balance a single cylinder crankshaft, a bob weight is attached to the journal of the crankshaft that represents 100 % of the rotating mass and the percentage of the reciprocating mass from the chart. This assembly is then placed on the ball bearing V’s of our Stewart-Warner crankshaft-balancing machine and spun up to the expected operating RPM setting. The balancer can read the change in weight on both sides of the crankshaft and precisely tell the operator the amount of weight that needs to be added or removed from the left or right counterweights to achieve optimum dual plane balancing.
Balancing a crankshaft in itself does not produce more horsepower; it improves output potential by eliminating or greatly reducing a non-productive use of horsepower. It also helps prolong the life of an engine by reducing damaging vibration. In any situation where some grinding of the crankshaft or modification of the piston is permitted, it is a largely untapped source of performance gain.

Setting Ignition Timing

2003-05-08T08:23:00.011-04:00

By Tom Cole
Almost every day someone calls or emails us asking how to set the ignition timing on their engine. It is an important topic because as little as one degree can be the difference between an engine that runs up front and an engine that sputters and pops its way to last place. In this article, I am going to describe what I believe to be the most accurate and reliable method to set the timing on a Briggs and Stratton™ Engine. If you are using an ARC adjustable hub flywheel, begin by setting the hub index mark in the middle of the degree marks on the aluminum body. This will give you the maximum amount of adjustability after you set the timing based on the cam manufacturer’s specifications. The adjustable hub gives you an “at the track” advantage, because it allows you to easily advance or retard the ignition timing to tune for variable conditions.
The first thing you must do to set the timing is to identify the exact position of the flywheel’s magnet in relation to the coil when ignition occurs. To do this right, you need a plain old induction timing light and a car battery. Some folks will tell you about aligning the trailing edge of the magnet with the center of the little button just in front of the left leg of the coil, and for the most part, they are correct. But there is no such button on the Animal coil and factors such as coil gap make this method only a close approximation. The diagrams below represent this approximate setting for some popular coil types:

Below is the technique I use to find the exact trigger point using a timing light:

Install only the crank, its bearings and its timing gear in the engine block and put on the side cover.
Install the sheet metal guard that goes behind the flywheel.
Install the flywheel with a standard key on the crank and snug it up with the starter nut. (No need to torque it, you are going to take it back off)
Install the coil with the proper gap. (It will not be removed so tighten it up)
Attach a spark plug to the plug wire and tape it to the block so as to ground it and create a spark.
With the magnet at 12 o’clock under the coil put a white line on the outside rim of the flywheel at about 3 o’clock. This line needs to be plainly visible when looking at the block from the front.
Attach the timing light to the battery and clamp the induction lead on the plug wire. Be careful that all wires are away from the flywheel.
With the timing light pointing at the front of the block, turn the crankshaft clockwise with a drill or starter and you will see the timing strobe light up the white line. You need to spin it faster and more consistently than possible with a pull starter because a magneto has a retarding effect at higher rpm, and you want to compensate.
While the strobe is flashing and the flywheel is spinning, make a white mark on the sheet metal guard or block that aligns with the white mark shown by the timing light on the flywheel. You can now place the magnet exactly where the spark is triggered when and if you ever remove the flywheel. BUT, if you move the coil or the metal guard, you have to start all over again.
Remove the flywheel, side cover and crank, and install the piston, rod, crank, cam, etc (leaving off the cylinder head) getting to the point where you are ready to install the flywheel and set the timing.

You are now ready to set the timing. Truthfully, it is more accurate to set the timing by fixing the piston at a measured distance before it reaches its highest point on the compression stroke. But, although everyone knows the “in the hole” distance for a pure stock setup, (30deg is .2115”) it is difficult to calculate the distance needed by different length rods since the distance traveled by the piston per degree of rotation varies with rod length and/or stroke. You can calculate it, but it just really isn’t worth the effort.

So, since the cam manufacturers generally provide you with a recommended ignition timing expressed in degrees before top dead center (BTDC) of the compression stroke, it is going to be best to set your timing using a degree wheel. (This is a good time to degree your cam too) On to the dreaded degree wheel…

Using coarse grit sand paper, rough up the tapered part of the crank and then make sure it is clean. If you are un-willing to lick it, it isn’t clean enough!
Similarly, rough up and clean the inside of the hole in the flywheel hub.
Set the crank so, according to the degree wheel, you are at the cam manufacturers specified degrees of ignition timing before the piston reaches the highest point of its compression stroke BTDC.
Put a few drops of Loctite™ on the tapered part of the crank and install the flywheel with the white timing lines aligned. DO NOT USE A KEY! Keys do very little to prevent a flywheel from spinning, and they will hinder your accuracy.
Carefully tighten down the starter nut. Check and recheck the timing several times as you tighten to be sure that the white timing lines are still aligned and that the degree wheel is still where it is supposed to be. Then tighten the starter nut, A LOT. You are shooting for tight enough to hold it together, but not so tight as to split the flywheel.
If you have an ARC adjustable hub flywheel, you can fine-tune your ignition timing using a dyno or a stopwatch and a Digatron CHT/Tach at the track.

That’s it! Once you have the timing set and are done with any track adjustments, measure the distance from the deck to the top of the piston (with the white timing lines aligned) and record the measurement. As long as you refresh the engine with the same parts, you can just set it in the hole and go when you refresh. If you re-deck the block, just subtract the amount removed from your recorded depth figure.

Is 1° Costing You The Win?

2002-04-12T08:30:00.000-04:00

By: Tom Cole
Do you REALLY know if advancing or retarding the ignition timing of your engine 1° will increase horsepower? I think most of us can agree that there is a good chance that we would find some improvement, if we checked. How easy is it to experiment with your motor? As I have said before, I am no expert. I am just a father like many of you who likes to build his son’s racing motors. I love the feeling when a motor I built takes the checkered flag, and I have felt the heat and disappointment from the driver (and the wife) when it is obvious that MY poor performing engine cost us the race.
One fact I have learned is that perfect timing is when your motor runs at the proper temperature, responds the way you want it to respond, and you win races. There are no magic numbers or exact calculations that can tell you where timing needs to be. There are only beginning reference points. Just like the carburetor, timing must be tuned to the conditions and variables specific to each motor, track, driver, and kart. Throw in the altitude and the weather conditions, and you can see that the ability to adjust timing quickly and accurately is something that can set you apart from the crowd.
Because the degree wheel infuriates me, and offset keys are a joke, I set ignition timing by aligning the trailing edge of the flywheel magnet with the middle of the coil trigger button while the top of the piston (before top dead center) is at a measured depth from the top of the cylinder. The depth of the piston in the hole varies with many factors, but your cam manufacturer will usually give you a good starting point. (30° BTDC = .2115” in the hole when popup is 0.000” on a stock engine) Once I have everything aligned, I carefully hand tighten the starter nut. Then I recheck my measurements, torque the starter nut down to somewhere around 1,000,000 in./lbs. (I give it all I’ve got with hand tools) and recheck my measurements again. Also note that I do not use an offset key. I lap the flywheel and crankshaft together and then apply Locktite™ to the taper (not the threads) on the crankshaft before installing the flywheel. Now I reassemble the motor, mount it up to the kart, and give it a test run. This whole process takes about 30 minutes.
Now how many of us are going to take that motor and go through that same process at least three more times to check and see if +or- 1° makes a noticeable difference? The method I use to set the timing has a margin of error of at least +or- 2° because I don’t know the exact firing point of the coil trigger button. I know I need to experiment, but what a pain! And how much stress am I putting on the stock flywheel each time I knock it off and torque it back down. Haven’t they been known to fly apart? And how well is that flimsy stock animal flywheel going to hold up? I have heard of engine builders breaking them when they are first installed!
It wasn’t until I faced all this trouble with that touchy little blue-plate slapper-cam motor that the value of ARC’s billet finned flywheel with its adjustable timing hub really came into view. I can literally be finished getting the motor’s ignition timing right with the ARC flywheel, before I can test the first timing change on a stock or fixed hub flywheel. How much time do you have at a race between practice and the first heat? I am too busy changing oil, cleaning and prepping tires, and making chassis adjustments to tear down a motor.

Rolling Resistance

2002-01-17T16:58:00.000-05:00

By: Tom Cole Date: January 17, 2002
Every rear wheel drive car or truck on the road or racetrack uses tapered roller bearings in their front hubs. The reasons for this are simple, less friction and combined radial (perpendicular to the axial) and thrust (parallel to the axial) load capacity. So why are kart racers using ball bearings which are designed only for radial loads on their karts? I can understand why Jr. Drag racers don’t care about thrust load. They just go fast in a straight line. But kart racers go fast and turn fast. Usually, the one who gets through the turns the fastest wins. So again, why are so many kart racers using ball bearings? Endplay! Somebody has actually sold people on the idea that karts with tapered roller bearing hubs have so much endplay that you can’t set the toe-in. What a pile! How is it that those NASCAR and F1 boys can set the alignment on their cars? Never mind that endplay tolerance for a wheel with tapered roller bearings is only .002” (that’s half the thickness of a piece of notebook paper). How precise are the widths of the inner and outer races of a .65-cent ball bearing? How precise is the relationship between the inner and outer races? Are they parallel? Are they precisely on the same plane? How precise is the bore of the hub? Is the center sleeve exactly long enough? Well guess what! None of this matters if you use a properly installed tapered roller bearing. The guy beating you doesn’t give a rip how the wheel rolls on the rack. How the wheels roll on the track, in the turn under thrust load and down the straightaway under radial load is what matters in wheel bearings. And he is not going to tell you why he’s beating you.

All ball bearings roll on a “point” of contact between the ball and the races. A tapered roller bearing distributes the load over the length of the roller in a “line” of contact. This greatly reduces the friction coefficient allowing tapered roller bearings of the same diameter as comparable ball bearings to carry a greater load and achieve a much greater fatigue life. Simply put, it will roll easier than a ball bearing. The angle of the races along with the taper of the bearing rods allows a tapered roller bearing hub to roll equally well in the turns or on the straight-aways. Standard ball bearings DO NOT roll as well through a turn as they do down the straightaway, and they do not handle the demands of a kart racer as well as a tapered roller bearing.

STROKER ROD DESIGN

2000-03-20T17:09:00.002-05:00

By: Carl Amundsen Date: March 20, 2000

Evidently a lot of people have read and paid attention to our editorial " Oil Clearance is Not a Myth But a Calculation ". We appreciate all the calls and hope it has helped save some engines.

A constant question that keeps coming up is about the bore size on the stroker rod for the .875 (7/8) journal crankshaft.

Why are the rod bores on some brands of stroker rods as much as .004" out of round, right out of the box?

These rods all have angled or what is termed "splayed rod bolts". This is a necessary design because of the amount of stroke in the crankshaft and the need for clearance at the camshaft and inside the block.

The problem occurs when the parting surfaces at the rod and cap are not 90 degrees to the rod bolts. On the illustration below the right rod bolt enters at 15 degrees and the left rod bolt enters at 7 1/2 degrees. The parting surfaces of the rod and cap are at 75 degrees and 82 1/2 degrees respectively to the rod bolt.

It is easy to see from the illustration that the seat area under the rod bolt and the seat area of the cap will be at an angle to the parting surfaces of the rod assembly. This is where the problem begins.

During the manufacturing process the rod and cap are assembled together and the bolts are tightened to a specific torque value. The final machining of the bore now takes place, and comes out on size and round. The next thing that happens is that the rod bolts are removed and new ones are installed. Here is your problem. Because of the adverse angle at which the bolts enter the seam of the rod, they pull the bore out of round. It will always come out egg shaped, and the more you play with the torque values the worse it gets. This is not a one out of ten problem this will happen 100 times out of 100 times. It can be bad enough to lock the motor up. Bet on it. THE PROBLEM IS IN THE DESIGN.

To add insult to injury, some rods are designed with the rod bolts exposed to the bore. This just reduces the integrity of the bore and weakens the seam area. If that's not enough, you must grind some clearance into the back side of the bearings to accommodate the rod bolts.

THE FOLLOWING IS AN ILLUSTRATION OF THE ARC DESIGNED STROKER ROD, NOTICE THAT THE BOLTS AND THEIR PARTING EDGES ARE PERPENDICULAR TO ONE ANOTHER. THIS DESIGN ELIMINATES THE PROBLEMS CAUSED BY THE ANGLED BOLT TO PARTING EDGE SITUATION. OUR WAY STILL ISN'T PERFECT, BUT IT IS A HUGE STEP IN THE RIGHT DIRECTION.

OIL CLEARANCE IS NOT A MYTH IT IS A CALCULATION

2000-02-08T17:21:00.000-05:00

By: Carl Amundsen Date:2/8/2000

Over the years I have had many opportunities to discuss oil clearance with engine builders. Some are building for their own use, some are small shops while some are large. In any event when the question is posed "HOW DO YOU KNOW WHAT YOUR OIL CLEARANCE IS?" the responses vary. Some can give a good mathematical response, some don't have a clue. The common denominator here is that everyone knows they have oil clearance.
A common phenomenon that occurs when a motor fails is that no one looks in the mirror for answers. The vast majority of the time it is blamed on an engine part failure. The connecting rod too many times is the favorite fugitive.
A LESSON IN MEASUREMENTS
A very dangerous but commonly used method of measuring is a dial caliper. The average dial caliper is super for measuring the thickness, inside diameter, and outside of an empty toilet paper roll. A SHOCKING STATEMENT , NO DOUBT! If you look through some catalogs you will find a dial caliper for $40.00 that has an advertised accuracy of +/- .008 . That is an error factor of 16 thousandths. Pay $200.00 for a digital caliper with advertised accuracy of +/- .0015, the margin of error is now 3 thousandths. An error factor of 1 thousandths can cost you a motor. Calipers are great tools for some things but not for the task at hand. WE MUST BE ABLE TO READ IN TENTHS OF THOUSANDTHS(.0001)
ON WITH THE LESSON
If you were to take a good 0 to 1 inch micrometer and measure the thickness of a page in the ARC catalog, you will find it to be five thousandths (.005) thick. This is very important to remember as you read on. Now feel the paper with your fingers and imagine somehow splitting one of these pages 50 times. One single sheet would now be 1 tenth of 1 thousandth of an inch thick (.0001). I hope I have your attention, because this is getting down so that you can't even feel the thickness. Just incase I am going to be confusing you with decimals please remember the following:
1.0000 = 1 inch0.1000 = 100 thousandths 0.0100 = 10 thousandths0.0010 = 1 thousandth0.0001 = 1/10 thousandth

It makes no difference who you buy your parts from, nor does it matter what brand they are, ARC included,they need to be checked and double checked. NOBODY IS PERFECT.
For example let's build a stock stroke Briggs racing engine. The following is the measurement specifications on the typical parts to be used:
Stock Briggs crank rod journal size......................... .998 +/- .0015Aftermarket Connecting Rod................................... 1.150 +/- .005Aftermarket Rod Bearing thickness........................ .075 +/- .003
ALL THE PARTS WE ARE USING ARE WITHIN THE MANUFACTURERS TOLERANCES.
You are going to use a medium weight oil and you are shooting for .0025
The Connecting Rod is on the small side................. 1.1495The Rod Bearing is on the big side.......................... .0753The Crankshaft is on the big side.............................. .9985
Let's put this motor together and go racing.
The Connecting Rod is small by .0005...................... 1.1495The Thickness of the Rod Bearingare big by .003(2 bearings) =.1506............................. - .1506Net Rod Bore size with Bearingsinstalled................................................................... . 9989The Crank Rod Journal is big by .0005..................... - .9985The Calculated oil Clearance = ............................... .0004We were shooting for ............................................... .0025
With a little luck this motor will crank up and run, as long as the motor is running at no load and a low RPM it may be OK for a while. The minute you go racing the lack of oil flow between the bearing and the crank journal will cause heat build up. The bearing will seize on the crank journal, break the rod and just make a mess of everything. BAD PARTS RIGHT ? WRONG !
Now let's build another motor and go the opposite way, still trying to achieve an oil clearance of .0025
The Connecting Rod is on the big side........................ 1.1505The Rod Bearing is on the small side.......................... .0747The Crankshaft is on the small side.............................. .9965
The Connecting Rod is big by .0005............................ 1.1505The Thickness of the Rod Bearingare small by .003(2 bearings) =.1494............................. - .1494Net Rod Bore size with Bearingsinstalled...................................................................... 1.0011The Crank Rod Journal is small by .0015..................... - .9965The Calculated oil Clearance = .................................. .0046We were shooting for .................................................. .0025
This motor is going to run, but what is going to happen here is: The bearing is going to get pounded at the top and bottom of the rod bore, because there is an air gap between the two surfaces. The oil is not thick enough to prevent this from happening. This is going to convert the rod bore into the shape of an egg standing on end. The crankshaft will now start to loose it's round shape and wear.
EVERY MINUTE IT RUNS, THESE PARTS WILL INCREASE THE OIL CLEARANCE UNTIL IT EXPLODES. HOW LONG WILL IT LAST? I CAN'T SAY EXACTLY, BUT NOT TO LONG!
The crying shame here is that everyone will point their fingers at the connecting rod, bearings and/or crankshaft as the culprit.
THE MOST OVERLOOKED AREA IN ENGINE BUILDING IS AS FOLLOWS:You have a motor that has run for many months , but you notice you're getting a little blow-by and it could probably use a set of rings. It needs freshening up so we tear it down. Every thing looks great so we touch the bore with a hone and put a new set of rings in. Back to the races. If it ain't broke don't fix it. STOP! Under the most ideal conditions engine parts will change with use. Bearings can look good but will wear, connecting rod bores will change shapes and crank journals will wear and rod bolts will stretch and fatigue. It is just as important now as ever to check the dimensions of the parts. Don't go to sleep.
Some may think there is some deep mystery behind the term oil clearance. The reason is, everyone has a different opinion as to what it should be. As a rule of thumb, it can be anywhere between .0015 and .0035 and be in the ball park. If the clearance is on the low side, use thin oil, heavy oil will not work. If clearance is on the high side , use a heavier oil, thin oil will not work. How can you make a judgment on the oil to use unless you know what your oil clearance is? THERE IS NO MAGIC, YOU CANNOT KNOW WHAT YOUR OIL CLEARANCE IS UNLESS YOU MEASURE THE PARTS THAT AFFECT IT.
DEFINITION OF WHAT OIL CLEARANCE IS:
"The distance between two very smooth moving surfaces that will allow oil to be present at all times, coating both parts with a film of oil so that metal on metal contact never happens. It must be small enough to retain enough oil and large enough to allow a fresh cool supply to move through every microsecond."
If you do not check your parts and build 4 motors and 3 of them seem to have a pretty good life span you are lucky. If one fails out of the gate or shortly thereafter, shame on you. It takes less than 15 minutes to check and measure all the parts in a motor and the benefits are fantastic. It is possible to build an engine that will run until the cows come home, or something like that. There are many engine builders out there that do a fantastic job in this area, but on the other hand there are more that don't.
ASSUME NOTHING, BELIEVE NOTHING AND LAST BUT NOT LEAST, CHECK EVERYTHING.
I hope we have given you an insight to one reason for engine failures. If you need us, give us a call, it's all free. 1-800-521-3560

The Jury is Back and the Verdict is In

2000-01-18T16:07:00.000-05:00

By: Carl Amundsen Date : January 18, 2000

The Case: To produce the best crankshaft ever.
The Jury: Engine builders, car owners, chassis builders from our customer base.
The Evidence:

The Material to be used
Much to do has been made about what kind of material should, could and would be used to make a crankshaft. Manufactures tout theirs are made of 4140, 4150, 8690, Stressproof, or other high mucky muck number designations. We investigated all of these options, but when the smoke cleared we came back to a material we had been using for 20 years. The material does not have a number designation because it is proprietary to the manufacturer and is patented. The brand of the material shall remain anonymous for our own reasons. The biggest user of this material is the mining industries, where it is used in augers, blades, conveyors or anything that requires a hard wear resistant material. We have used this material for 20 years in impeller blades for steel shot machines. Through its manufacturing process and mineral content it requires no hardening before it is used. It comes in the door with a hardness of 44 to 46 on the Rockwell "C" scale and the more it is used the harder it gets. This is all accomplished without it becoming brittle. The only negative side of this is that it is a nightmare to machine. It took about 6 weeks of trial and error to come up with the right feed rates and spindle speeds. The only tooling material that is compatible is solid carbide. Tool life at best is very expensive.

Design and Engineering
Instead of taking a brand new crankshaft out of the box and starting the process of cutting and grinding. This is not necessary with ARC cranks for most applications of camshafts and lifters etc. You will also find that there is no note in the box instructing you to deburr sharp edges, this has already been done. This was one of the more important items that we addressed in the manufacturing process. At least 15% 0f the machining time is spent removing sharp edges. This is an absolute must , this is also the reason other manufacturers simply leave you a note in the box. A sharp edge is an invitation for a crack to start, and no matter how small it is, it will grow just like cancer. I am sure everyone has seen the old trick of tearing a telephone book in half, same principal. We borrowed technology from NASCAR in designing the (airplane wing ) airfoil style counter weights. NASCAR has proven that it improves windage in the crank case and increases horsepower. The crank pin even has a true 1/8" radius for added strength and durability. Other crankshafts advertise that they are already balanced, NOT. We went through a very pain staking design process to make sure we could and should advertise a balanced crank. You will without a doubt notice the difference. ARC provides two differently balanced models of the +.563 stroker, one is balanced for the smaller bore up to .190 over and the 3 x 3 for the large 3 inch bore. Appearance, cosmetics and detail have always played a major roll in parts produced by ARC. I think we raised the bar on this one. Besides our logo, all ARC crankshafts are engraved with the part number and the date the part was manufactured. Little more can be said until you hold one in your hand, this crank is truly a work of art. Its worth mentioning , if you haven't already noticed, ARC has a habit of not following what the industry thinks or does. If we can't do it better, we just don't do it.

The Testing:
The latter part of August 1999 we made our first live test. You might think this is a crazy way to start testing, but we needed to build a motor that would come apart fairly easy, I mean explode! This was done with a blockzilla block, our new +.563 crank, an old .190 over piston with new rings, a used 4.225 rod with old rod bolts and a used 436 lift camshaft. We knew from the start that the rod bolts and/or the rod should break, they just had to much time on them. If our crankshaft was going to live it would have to withstand this. The tension and anxiety is growing. Over the next four weeks we made over 250 passes down our local 1/8-mile drag strip, seeing RPM's in excess of 9600. Nothing happened. Not being able to break it was becoming very frustrating. The next test we felt sure "The old wore out rod and bolts" would fail, and we would have our desired results. We put the motor on a kart chassis and ran it on the local 1/4 mile asphalt oval. This is the hardest test on any motor because you are constantly in and out of the throttle. We now had shipped a number of crankshafts to select customers with their promise to have them in motors very quickly, and report to us with results.

The results from the field are as follows:
"That's a beautiful part, works great.""Smoothest running motor I have ever seen, what did you do to it ?""I can't believe this , it's great !" "How soon can I get five more?" And so on. Everybody loves it and no one has had any problems.
We were now getting well into October and getting a little curious , what will break it ? We have over 125 laps on the kart and the motor just purrs. The only maintenance we had done was keeping oil in it. It was even suggested that we run it without oil, dumb idea of course but we were desperate for some results. We didn't do that obviously. At this time we turned the motor over to a local drag racer to finish the job. Finally some results. One of our crank shafts had made it through one of our renowned engine builder customers well west of the Mississippi and back to San Antonio , Texas. Charlie Bass Sr. and his son Charlie Bass Jr. are kart racers that race an outlaw class against the highly touted 2-cycles. However they use a Briggs Blockzilla. Over the past year they were using a 563 stroker crank of an origin I will not mention. They had the power they needed to lead and win races but kept breaking crankshafts. NEED I SAY MORE ? YES, I WILL! THEY WHIPPED EVERYONE AND WENT ON TO BECOME POINTS CHAMPION! A footnote to this is he always used ARC rods.
CONGRATULATIONS TO THE BASS FAMILY, WE LOVE YOU !
Texans have always laid claim to being a little different and I wouldn't debate that. Charlie Sr. had a strikingly different approach for checking for burrs and rough edges on our crank. He wiped the crank down with a pair of panty hose, and did not get a run in them. I didn't ask who the panty hose belonged to.
More Comments
"We no longer have to hold the kart down on the rack when we run the motor, it just sits there and purrs." " I can read the temp. gauge and tack now, I can see the flags." Charlie Bass Jr. " Is this smooth or is this smooth "
At their request we have put the Bass' in the unprotected witness program.
Charlie Jr. Leddfutt24@worldnet.att.net

Charlie Sr. DrBriggs94@worldnet.att.net Home phone 210-923-5730
THANKS AGAIN TO THE BASS FAMILY

Now back to our test motor. We were closer than we thought, it only took two more weekends of racing to do it. When we tore it down the rod bolts had broken along with the rod (as we predicted) and chunked the whole mess out of the side of the block. FINALLY RESULTS WE WERE WAITING FOR. WHEN WE BUILT THIS MOTOR WE INTENTIONALLY USED AN OLD ROD WITH OLD BOLTS, THAT SHOULD HAVE BEEN JUNKED. WE KNEW THE ROD WOULD BREAK , WE JUST DIDN'T KNOW WHEN. The crank was still straight, the crank pin was still in perfect shape and the only damage was some scuff marks on the counter weights. We checked the hardness of the crank pin and it had gone up 5 pts. on the Rockwell scale. Magnaflux revealed no stress or cracks. Anyone in his right mind would think surely this is enough, NOT US. What everyone wanted to see now was just what would break it. GET THIS, the stage was set, the crank was placed in a hole in our heavy duty welding bench which is two inches thick. The crankshaft was vertical with one counter weight resting on the table. Our weapon of destruction was a 10 lb. sledge hammer with a 36" handle powered by Randy Amundsen. Smashing down on the exposed counter weight, we wanted to see if the counter weights would touch before breaking the crank pin. To me this seemed cruel, it reminded me of the turkey losing his head Thanks Giving morning. This crank surely didn't have a chance.
LET THE CONTEST BEGIN
After 5 or 6 hits the crank was holding up fairly well. After about 12 hits the crank was bending but still refused to crack. Someone muttered " that crank thinks Randy is a wimp". After more than 25 over the head death blows the crank finally gave up. Before Randy could catch his breath another brand crankshaft was set up ready for the same challenge. Two smashes latter we knew who had the toughest crankshaft on the market. This was ARC's real world extreme testing at it's best and our new crankshafts finest hour.
CASE RESTED.

THE VERDICT
1. Its design and engineering is well thought out. 2. The appearance and cosmetics leaves the competition in dust 3.The balance is superb. 4.The strength is probably beyond necessary. 5.The price is higher but well worth it. 6.Go to market.

SUMMARY
ARC has created a crankshaft with limited sales potential. It is going to last the customer too long and greatly reduce repeat sales. It may create for the first time in history, a USED CRANKSHAFT MARKET.

Probable Cause of Most Rod Failures

1999-06-01T08:35:00.000-04:00

To help prevent engine failure, here's a few tips:
For the most part, a quality billet connecting rod doesn't just break. There are several things that can really shorten the life of a rod of which bearing clearance is probably the most important and too much is worse than not enough.
Visual inspection (or eye balling) is not good enough. The only way to check a crankshaft, rod or bearing is with micrometers and dial bore gauges. Dial calipers or digital calipers are just not accurate enough. Even with the ones that have .0005" graduations, the accuracy is generally + or - .001" which means outside to inside measurements could have a total error of .004".
The Crankshaft:Just because a crankshaft looks good, doesn't mean it is to size and round.Using a 1" micrometer, measure the rod journal of the crankshaft in 4 places. A crankshaft with more than .0005" wear or out-of-round will probably not last very long in a 9500 rpm race environment.Keep in mind, what you might get by with in a stock engine, will not be as forgiving in a high rpm, high horsepower engine.
Surface finish of the rod journal is also very important especially when a babbit bearing is used. Most of the new Raptor III cranks I've seen and checked are way too rough.
Bearings: One of the most common things we hear is "The bearing looked ok, so I reused it"Again, looks can be very deceiving. Take a 1" ball micrometer or use a ball anvil attachment on your mic to measure the bearing thickness in several places. The ball anvil is necessary because of the curvature of the bearing.The measurement should be .075" and, on a crankshaft that measures .998" on the rod journal, this should give you .0025" clearance.
On a bearing that has been run or has been honed or sanded for clearance, carefully mic each half on the outside edges and in the middle.Remember, a new bearing should measure .075" which should give you .0025 clearance. If the top bearing measures .073" and the lower bearing measures .074", you now have .0055" clearance.
Some engine builders use a ball type hone to clearance bearings and this can cause a major problem. The Babbitt material is very soft and easily removed. What happens is that as the flex ball hone enters and exits the bearing bore, it removes far more material from the edges than from the center producing an hour glass shape. Using a plastigage or measuring the bearing in the center may give you a false and possibly fatal reading.You may think you had .003" clearance (and you did in the center) but, it will be a very narrow contact area and wear rapidly and as this clearance increases, it compounds the problems.This additional clearance pounds the bearings until the rod & piston assembly becomes a 9000 rpm slide hammer. This is when you have a failure.
Special note: Never file or grind the ends of a bearing. If the installed i.d. of the bearing is too large (measured inside diameter of the bearings installed in the rod and torqued too 150 inch/pounds), gently and slowly remove material from the parting edges of both halves with fine emery cloth on a flat surface until you get an installed i.d. of .9995" to 1.0015" for stock .998" cranks and .8765" to .8785" for stroker .875" cranks. It is better to sneak up on this slowly.
These bearings are designed to crush in the bore of the rod which holds them in place and prevents them from spinning. The tangs are primarily for location. If your crank measures less than .997" or .874", it is probably a good idea to replace it. In any case, it is not a good idea to try to compensate for a worn crank journal by reducing the i.d. of the bearing.
Inspect and/or replace the bearings regularly. By examining the bearings, you can set up a schedule of how often to replace them - plus - by measuring and looking for excessive smearing or wear-through of the babbit material, you'll be able to tell if your oil is doing its job.
Rod Bolts: Proper rod bolt torque is VERY important. In order to keep from backing out, it is necessary for a bolt to stretch a specific amount so the threads lock into place. This is a little known or understood requirement for a bolt to do the job it is designed to do. The proper stretch for a bolt is usually achieved by torquing the bolt a calculated amount based on the bolt's design and the characteristics of the application. ARC's rod bolts are custom designed to achieve thread-lock at 170 inch/lbs. This MUST be measured with an accurate inch/lb torque wrench. Failure to properly torque the bolts is a all to common cause of rod failure, second only to the oil clearance issues explained above.
Treat your engine as the piece of precision equipment that it is. The environment in which it operates is extremely harsh and attention to detail along with precise measurements is absolutely necessary.

The Crankcase Vacuum System (CVS)

1999-01-07T17:07:00.000-05:00

By: The ARC R&D Team Date: January 7, 1999
Re: Crankcase pressure management

For as many years as I can remember, crankcase ventilation went like this:
If you were blowing oil and having gasket and seal problems, you just added another line from your motor to the catch can. I have seen as many as 6 lines running from a motor, but the problem was still there.
In case you didn’t know it, we were just adding insult to injury.

Viewed from the crankcase, the single cylinder motor is an excellent air compressor. The more air you take in, the more you have to push out somewhere. Consequently the more air that is being passed through the crankcase, the more oil that will follow the air out.

All small engine manufactures have done a fair job in their crankcase ventilation system, but it only works up to about 3,000 rpm.

NASCAR and the Drag Racing industry have long used a dry sump oiling system that also creates a negative pressure (or partial vacuum) in the crankcase.

A multi-cylinder engine is a little simpler to deal with because one piston going up is canceling the pressure of the other one coming down. The basic thing you are dealing with here is called blow-by.

Without getting into a long technical and complex discussion on the subject, let me just make this statement. The rings on the piston are designed to work at their maximum with pressure from the top and vacuum from the bottom.

Common sense will also tell us that the piston will function much better and develop more horsepower if it is being pushed down in a negative pressure environment. In fact, with vacuum in the crankcase, the piston is actually being sucked down the cylinder wall.

Any positive pressure in the crankcase will allow a certain amount of oil to get passed the rings and contaminate the fuel charge. This can and will reduce horsepower.

Our Crankcase Vacuum System is very complex in design and every hole, groove, passage and vent are critical to its successful operation. Even the length and size of the tubing used in the catch can model for Kart racing are critical.

While the design is very complex, the operation is very simple to explain.

Without the CVS, the tappet room (valve spring area) is continually being flooded with oil and, contrary to popular opinion, this volume of oil is NOT being caused by the length or design of the dipper on the connecting rod - the cam gear is the culprit.
A little side note right here on horsepower. If the tappet room is flooded with oil and the valve guides are a little on the sloppy side, oil can easily be sucked by the valve stem and contaminate the fuel charge.

Our CVS works like this:
As oil and air are being pushed up to the tappet room, the first baffle is atomizing the oil and lubricating the valve stem with a mist. The second baffle is now starting to separate the air from the oil.
The 2 check valve discs are sensing the blow-by of each down stroke of the piston, regardless of how minute the amount, and are opening and closing on each stroke.

When the piston is at the top of the stroke, we will have our maximum vacuum. When it nears the bottom, vacuum gives way to the amount of blow-by pressure from the rings. The best calculations we can come up with is that we have vacuum 95% of the time and little or no pressure 5% of the time.

As the mist of oil and air move through the CVS, we are continuing to separate the two in our maze of holes, grooves and passages.

In the final step of this unique process, we are now using the vacuum in the crankcase to pull the oil, which is heavier, back into the crankcase, and the oil free air is vented.
AND THAT’S JUST HOW SIMPLE IT WORKS !

While the operation is simple, the R&D on this project has been the most intense of any project we have ever undertaken at ARC Racing. The Dyno testing has been extensive, not only by us, but other engine builders as well along with track testing that has been on going for months.

The results: THIS UNIT HAS MADE HORSEPOWER ON EVERY SINGLE TEST.

Dual Plane Balancing

1999-01-07T08:38:00.000-05:00

We receive lots of calls about balancing and one of the first questions is always, "What is DUAL PLANE BALANCING".
If you read the book on it, and you had a background in engineering and physics, you could get a good understanding of it. The two terms that are used in the explanation are Force and Couple balancing. What we are going to attempt to do is reduce all of this down to a non-technical explanation.
Lets go back many years to tire balancing. Your rim and tire assembly was mounted on a shaft and then placed on a frame with the shaft resting in a ball bearing V fixture. The tire assembly would then rotate around until the heavy part came to rest at 6 o’clock. A wheel weight was then placed at 12 o’clock on one side of the tire. You kept adjusting this weight until the tire would not move regardless of how you repositioned it in the V fixture.This process is called, Static or Force balancing.
Then an improvement was made in this process. Instead of putting all the weight on one side of the rim, it would be split with ½ of the weight going to the inside. This was the first form of Couple balancing in the tire industry. Not perfect, but an improvement.As years went by, and the advent of much wider tires came into being, the need for Couple balancing increased.
We know have electronic tire balancers that spin the tire assembly and calculates the amount of weight needed to Force balance. Then it calculates what amount goes on the inside of the rim and what goes on the outside. This is Dual Plane balancing of a tire.
How does Dual Plane Balancing apply to the Briggs Crankshaft ?
A bob weight is attached to the rod journal of the crankshaft that represents 100 % of the rotating weight and a percentage of the reciprocating weight. This assembly is then placed on the ball bearing V’s of the balancer. It is then spun up to the operating RPM. Now the balancer can read both sides of the crankshaft and precisely tell the operator the amount of weight that needs to be added or removed from the left or right counter weight.This completes the Force and Couple (Dual Plane) balancing.
Special Note:If you change the connecting rod and/or piston, wrist pin and rings, the crankshaft may need re-balancing.

Stock Briggs & Stratton 5 hp.Calculation Formulas

1998-11-11T09:00:00.000-05:00

Calculation Formulas

Stock Briggs & Stratton 5 hp. specifications:
Deck height: 6.2835"
Rod length: 3.8750"
Compression height: 1.1900"
Rod bore (crank): 1.0010"
Rod bore (wrist pin): .4910"
Cylinder bore: 2.562"
Stroke: 2.4370

Measuring Stroke
Stroke is measured from the center line of the crank bearing journal to the center line of the rod journal multiplied by 2.

Measuring Deck Height
Deck height is measured from the center line of the crankshaft bore to the deck of the block.

Measuring Compression Height
Compression height is measured from the center line of the wrist pin bore to the top of the piston.

Calculating Cubic Inch Displacement (cid)
To calculate cubic inch displacement (cid):multiply bore x bore x stroke x .7854example: 2.562 x 2.562 x 2.437 x .7854 = 12.5633 cid

Rod Length & Compression Height - Made Simple

Calculating Rod Length
To calculate rod length:subtract deck height - (stroke divided by 2) - compression height.example: 6.2863 - (2.437 / 2) - 1.190 = 3.875 rod length

Calculating Compression Height
To calculate compression height:subtract deck height - (stroke divided by 2) - rod length.example: 6.2835 - (2.437 / 2) - 3.875 = 1.190 compression height

Does It Matter? A common sense approach to engine building.

1998-11-11T08:39:00.002-05:00

Historically, human nature has taught us two basic things about the question "Does It Matter ?"
1 - If a problem exists, and we have the capability to correct it, we tell the world "It Does Matter".
2 - If we don't have any interest or desire to correct a problem, we either keep our mouths shut or simply say "It just doesn't matter".

PREFACE
This article could have been greatly expanded into a full length novel but would have gotten boring with illustration on top of illustration.What's written here is not fiction, and mixed with a bucket full of common sense and imagination, you will run faster and longer.If you disagree with our opinions, let us know. We can learn too.If you have any questions or problems, send us an e-mail or call 1-800-521-3560. We'll be here if you need us.

DOES IT MATTER
If the base of a block is not perfectly flat and true ?If the surface of a motor mount that accepts the base of a block is not true and flat ?Through no fault of the chassis builder, it’s virtually impossible to have the mounting rails for the motor mount perfectly aligned.Does the weight of the driver flex or move the motor mount rails on the chassis ?Do the motor mount rails move and flex during a race ?
In other words, can you take a perfectly good motor, bolt it to a motor mount and then to the chassis and totally mess it up ? And the answer is - YES !

CONSIDER THE FOLLOWING TEST RESULTS
We took a block and precision align bored it perfectly round and straight from top to bottom and bolted it down to a rigid, perfectly flat surface plate. Under one corner we put a .050 shim. This shim could now represent a distortion caused by any one of or combination of the problems mentioned above.Next, we took a good tenth (.0001) reading dial bore gauge to examine the bore. Looking at the top of the block, and considering between the two valve seats would represent 6 o’clock, we took 2 readings. One aimed at 11 o’clock and one aimed at 1 o’clock. Starting at the top of the bore we moved down a ½ inch at a time. As we moved down the once perfectly round bore, it started taking the shape of an egg.The distortion was .002.
This test was performed on a Kool bore motor bored .030 over.The crankshaft bores had also moved and were slightly tighter in the DU bushing.A dual bearing block is more forgiving when this happens but either way it is a problem.The deck of the block also moved and became distorted.
Here’s a shocker:Before we did the test, we bolted a side cover on the block without a gasket and could see day light between the two surfaces. Then we took feeler gauges and it was easy to find where a .002 gauge would fit but we also got a .004 gauge to fit in one place.
Have you ever wondered why sometimes you have problems with oil leaks and blown side cover gaskets ?
These are some problems that can happen because of this:
• Scuffing or galling pistons.
• Abnormal wear in the cylinder wall.
• Rings not seating.
• Loss of compression.
• Loss of horsepower.
• Increased blow by in the crankcase.
• Oil consumption.
• Oil contaminating the fuel charge.
• Engine life short lived.
• Blown head gaskets.
• Side cover gaskets leaking.
• Blown side cover gaskets.
• Blocks cracking because of stress.

The question is: DOES ANY OF THIS MATTER ?
The answer is: ABSOLUTELY...

OTHER THINGS TO THINK ABOUT (and remember)
Briggs blocks are not equal and will vary from block to block.Kool bore blocks will distort more than IC blocks.Big overbores will distort more than stock bores.Pre-Raptor motors, with thinner castings, will distort more than the current castings.Large overbores for sleeves and then boring the sleeve for large pistons will distort even more.Over a period of years we have heard the following question asked several times a week from our customers:"I built two identical motors, 1 runs super and the other is a real dog, what’s wrong" ?or "I dyno tested this motor and it was great, then put it on the chassis and it wouldn’t fall out of a tree by itself. Why" ?
I wonder if anything we have discussed so far would shed any light on this subject ?

SOLVING THE PROBLEM
To solve one of the problems, the base of the block must be surfaced perfectly flat. The side cover must be on the block when it is surfaced. If you ever change side covers you must check the new one and make sure it does not stick down below the base surface of the block. If it does grind this material away.
The two drain plugs should be installed in the block TIGHT before it is surfaced. The reason here is that the drain plugs swell the block and create a knot on the base surface. Either before or after surfacing the base, with the drain plugs installed, take a die grinder and remove about .050 of material. The area to work on is 1 inch to the right and the left, and into the center of the block from the drain plug.
One last important thing:You must change your habits because you never thought about protecting the base of the block before.A special fixture (part number 7718) for milling or grinding the base of the block is available from ARC. This fixture also aligns the crankshaft parallel with the base of the block and aligns the existing bore 90 degrees with the base front to rear and is also excellent for use prior to boring a block on a vertical mill.

THE CYLINDER WALL • DOES IT MATTER ?
Ask yourself this question. Would you go to a race and add some oil to your fuel and loosen your spark plug just a little so you would have less compression? Obviously not. But you might be accomplishing the same thing and here’s how.Remember this rule of thumb. For every .001 wear on the diameter of the rings, and or the cylinder wall, the end gap of your rings grow by .003.
The following are some common examples of imperfect cylinder bores:

THE BARREL BORE
This cylinder measures the correct size at the top and the bottom of the bore but it is .004 bigger in the middle.You set the end gap of the rings at the top of the cylinder correctly but the end gap of the rings open up an additional .012 when they get to the middle of the bore.

THE UPSIDE DOWN FUNNEL BORE
This cylinder measures the correct size at the top of the bore but is .006 bigger at the bottom.You set the end gap of your rings at the top of the cylinder correctly but when the piston gets to the bottom of the stroke, the end gap opens up an additional .012.These examples may or may not be exaggerated, but its all relevant.

THE MORAL OF THIS STORY
The end gap of the rings and the correctness of the bore is a very controllable loss of compression to the crankcase and oil is being forced past the rings to dilute the fuel charge. ITS JUST HORSEPOWER BEING WASTED. Now stir this problem in with the first problems of distortion and you might as well call in the dogs.

Two more examples of imperfect bores:

THE FUNNEL BORE
The cylinder measures the correct size at the top but is .006 smaller at the bottom.

THE HOUR GLASS BORE
This cylinder measures the correct size at the top and bottom of the bore but is .004 smaller in the middle.You set the end gap of your rings at the top of the bore correctly but as the piston gets to the middle of the bore we have what is known as a CRUSHED END GAP. The cylinder wall galls, heat builds up and rings lock onto the piston. Need I say more.

WHAT IS GOOD ENOUGH IN A CYLINDER BORE
Perfection in any area is highly improbable but, as a rule of thumb, it should be within (.0005) ½ of a thousands. Holding the tolerance to less than this is certainly possible, so never give up trying at perfection.You should own a very good dial bore gauge that reads at least in the ½ thousandths (.0005).
When a motor is ready to compete in a race, the cylinder wall should be as perfect as possible. The bore should be round, straight from top to bottom and aligned exactly 90 degrees form the crankshaft. The cylinder wall should be as slick as possible with the rings already seated to the cylinder wall. The ring end gap should be at a minimum of .004 to .005" and the clearance between the piston and the cylinder wall (depending on preference) can be between .004 and .008.

ENGINE BREAK-IN • AN ELECTRIC RUN-IN STAND vs. LIVE RUNNING
There are many methods and theories on breaking in that new motor. The end result is that all the parts, especially the rings and cylinder wall, must wear a small amount to become compatible. WE MUST SEAL THE CYLINDER. Anything that is moving inside the engine is going to wear to some degree. During this break in period, all the metallic debris is being splashed back on these new parts causing more wear.
The big difference between these two methods:An engine running under power is under far more stress because of the pressures created by combustion. Therefore the metallic debris is under more pressure as it circulates over the moving parts. Fuel contamination of the oil is another problem. Fumes and noise are certainly a negative. Depending on motor design, engine RPM is sometimes hard to control. Ring end gap must be set at .004 to .005 because of the combustion heat. When the rings and cylinder wall have seated the end gap on the rings will now be .008 to.009.
An engine running on an electric motor run in stand is not under the stress of compression because we are running without a spark plug. At approximately 900 RPM we have a much more friendly environment to allow these parts to seat in. We are developing heat in the motor and it can run for several hours unattended with no noise or fumes. You can stop and change oil conveniently. The motor can even run without the valves, camshaft or lifters.The biggest benefit: Your engine can run with the ring end gap set at .001" which allows the rings and cylinder wall to wear and seat with a final end gap of about .004 to .005".
As you can see, by now, we believe that ring end gap is very important. Some of you are going to take issue with us and say that it should be .007 to .008 or more.The only thing that you have to worry about when you have the end gap at .004 is, MAKE SURE YOUR MOTOR IS AT OPERATING TEMPERATURE BEFORE YOU RACE OR LOAD THE MOTOR. Ring end gap is a controllable leak of compression.
Lets stop here and discuss a very important process.

PLATEAU HONING – WHAT IS IT?
After you finish hone your block to size with a nice cross hatch pattern and could look at it under a magnifying glass, you would see little peaks and valleys.These sharp peaks are going to be scraped of very quickly when the motor is first run. All of this metallic debris is going to be circulated through the engine.
Plateau honing is nothing more than wrapping a fine piece of wet or dry sand paper around your hone and with very light pressure make 2 passes from top to bottom. We now have Plateaus and valleys.
This is really important if you are using cast iron rings. These rings are porous and softer than chrome rings and the fractured material coming off the cylinder wall will become imbedded in the ring. When this happens it becomes increasingly difficult to seal the cylinder. Chrome rings are not effected by this material.In any event, plateau honing is well worth the time and in fact should be done on every motor.

Another subject worth mentioning:

JUST WHAT IS CLEAN?
Most parts will come clean enough in a good solvent bath. THE DEFINITION OF CLEAN FOR A CYLINDER WALL IS, A BUCKET OF HOT SOAPY WATER AND A SCRUB BRUSH. Then when you think you have it clean take a white rag dampened in solvent and wipe the bore. Now, is it clean?

THE SUBJECT OF RING SEATING
As we have discussed earlier, seating happens when the cylinder wall and the ring wears enough to seal the bore. If you inspect the bore after this has happened you will find that the cross hatch pattern has partially worn away and the bore is a lot slicker and the rings are polished the full 360 degrees.

CAST IRON RINGS vs. CHROME RINGS
Cast iron rings are easier to seat, are porous and will retain oil.Your final honing should be done with 320 grit stones and plateau honed with 600 grit sandpaper.Chrome rings are harder to seat and the surface finish will not retain oil.Your final honing should be done with 280 grit stones and plateau honed with 600 grit sandpaper. It may take a little longer run in time to seat them also.

FIGHTING FRICTION
The rings have already done a good job of reducing friction, but we can take this a little further. This, however, is another one of those subjects that there are many opinions on and we are probably going to step in you know what. But here goes…
As we stated earlier, chrome rings will not retain oil on their surface but cast iron rings will. So it is imperative that the cylinder wall has a texture that will hold oil.
In theory, after the rings are seated there should never be a metal to metal contact between the rings and the cylinder wall. It takes a thin film of oil between the cylinder wall and the rings to maintain the seal and keep the two parts from wearing. If this doesn’t happen, you can call in the dogs, the hunt is over.

A SECOND HONING PROCESS
Take a piece of 600 grit sandpaper and wrap it around your hone and with very light pressure, hone the block. This should only take a couple of minutes. The cylinder wall should remain bright and shinny. If you use to much pressure, or spend to much time in the bore it will start to look dark and you are now burnishing it. That finish will hurt oil retention.THIS FINAL PROCESS CAN ONLY BE DONE AFTER THE RINGS ARE SEATED.

IMPORTANT: WHEN YOU ARE BREAKING IN THE MOTOR NEVER USE YOUR RACING OIL. USE YOUR FAVORITE OIL THAT YOU PUT IN YOUR CAR OR TRUCK.

BREAKING-IN A MOTOR
We are going to use an electric motor run in stand, a leak down tester and a crankshaft locking bar.First, assemble all the internal parts in the motor, set the proper valve lash and install a breather plate. Do not install the cylinder head at this point.Fill the motor with your favorite engine oil.Secure the motor on an electric motor run in stand, bring the piston to top dead center and install the crankshaft locking bar.Install the cylinder head. Install the Leak Down Tester.
What we are going to do is a leak down test before we ever run the motor and document the results. Now as we go through the break in we can test periodically and measure our progress.
Remove the leak down tester and the crankshaft locking bar.Do not install the spark plug.Set the timer on the run in stand for 1 hour.
Now, make another leak down test and document your results.Run for another ½ hour, test and document your results.At some point, there will be no improvement and its time to stop.
The documentation will be a handy reference for future testing.
Now its time to disassemble the motor and do our final honing for friction. After that is done the parts need to go through the cleaning process and be reassembled for the final run in test.
Repeat the previous run in test (it should only take about half the time).
Document the results for future reference.

LEAK DOWN TEST RESULTS
The following is a good rule of thumb:
8 % - Something is really wrong
5 % - Just OK
4 % - Good
3 % - Very good
2 % - Excellent
1 % - Unbelievable
0 % - Almost impossible

This break in process can be done without the leak testing and for that matter without the cam and lifters. Your first run should be about 3 hours and the second about 1 ½ hours.

A BORING & HONING STRESS PLATE • DOES IT MATTER?
This subject is probably one if the most misunderstood areas we can discuss, and some will take us to task for our theory and opinions but here goes…Most people think a stress plate bolted to the top of a block pulls and distorts the cylinder bore, this is not quite true. However there is one exception were it possibly can, and this is on a very wavy and untrue deck surface. Were not going to build a motor with this kind of problem anyway, so it really doesn’t matter.

I KNOW, YOU’RE READY TO ARGUE, BUT I DID GET YOUR ATTENTION.NOW LET ME EXPLAIN WHAT REALLY DOES MATTER.

When a head bolt penetrates the threaded area of the block nothing happens until it is tightened down to the proper torque specifications. What happens then is a knot or swelling occurs in the bore of the block at the exact depth of the head bolt. And that’s all there is to it. Simple right, not quite.
Equal bolt penetration and torque on the bolts moving from the stress plate to the cylinder head should be a good match and this is the key.Quite naturally, all blocks are not equal and the amount of swelling into the bore is different. Kool bores, IC blocks, old style blocks, overbores and sleeved blocks are all going to react differently.Clean, undamaged bolt holes and bolts are also important.If you don’t have a stress plate, you can use a short piece of tubing and head bolts to accomplish almost the same swelling, but a stress plate is the best.
USING A STRESS PLATE DOES MATTER !
One last thing on stress plates. There are a number of people who won’t grind the valve seats without a stress plate on the block. My opinion is that it does no good.

THE SUBJECT OF CYLINDER HEAD STUDS
This is another subject that is controversial and I’m sure there will be some disagreement on our opinion.I do not like studs and can see no benefit from using them. Plus, they can cause a lot of problems.While there are many illustrations I could give you, the following is a classic one.You have a block ready to build and, for whatever reason, you decide to use studs.The block has been bored and honed properly - and it is perfect.
Now, you install a set of studs and tighten them down. If you stop just when they run out of threads, and they are nice and snug, you probably have already pushed a knot in the top of the bore. This lump only goes down about .125 but it is different than the one caused by the head bolts. This one is caused by the tapered conclusion of the threads ending on the stud.
Lets assume the piston fits and this goes unnoticed. The head is installed, and the proper torque is applied, but the stud decides to turn a little more and push’s more metal into the cylinder wall. No need to go further because this ball game is over.I could give many more illustrations, but I hope you got the message.
IF YOU FEEL YOU MUST USE STUDS, FOLLOW THIS PROCEDURE
Before you do any boring or honing:
• Clean the threads in the block and the studs with alcohol and let dry.
• Screw the studs in with a good coat of Lock-Tite. (it can take up to 24 hours for the Lock-Tite to cure)
• Now, using a stress plate, do your boring and honing.

VALVE GUIDES • DO THEY MATTER?
The valve guides that come in a new Briggs block are loose and sloppy and one thing is for sure, the valve will never stick. It is not uncommon to find them misaligned with the lifter bore. This can cause abnormal wear and valve seating problems. As far as using them for a racing engine they certainly come up short.
A full length brass guide is better, such as stacking 2 Briggs guides on top of each other. However the full length phosphorus bronze guide from ARC is the best.The ARC Bronze guide can be run with .0015 clearance on the exhaust, .001 on the intake and out last several sets of valve stems.A must with either brass or bronze guides is a smooth finish on the valve stem.
There are many people who feel a loose valve guide is the best because it reduces friction, but an ARC Bronze guide properly fit at the above tolerances will have little or no friction.Remember: Loose valve guides will contribute to oil contamination in the fuel charge which reduces horsepower.
The biggest problem with a loose valve guide is the poor little valve trying to find the seat at high RPM. Think about this: at 6000 rpm a valve must find the seat and seal it perfectly 50 times a second. Seems to me it needs all the help it can get.
ARC has complete valve guide installation equipment available that’s quick and easy, and also corrects any mis-alignment between the lifter bore and the valve stem.

SOME WORDS OF WISDOM AND CAUTIONS
Leak down testing is a very handy tool to use for determining if you have a problem with a motor or if it is still race worthy.
The compression ratio of an average stock Briggs motor is about 6.02 to 1, it would be very hard to increase it much with out killing flow and flame travel.
If cranking compression (with an electric starter) is 150 psi, on a great running motor, the compression at 6000 rpm will only be about 20 psi (or less).
Without a sealed cylinder, compression will just disappear at high rpm and guess what, the motor slows down.
If your motor is not running up front, and you make a header change, gear change, carburetor change and nothing seems to help. Do a leak down test and you’ll probably find the problem.
When you drive a new valve seat into your block, you will distort the top of the bore.
The average racer spends much more time tweaking and worrying with a camshaft than he does with sealing and maintaining the cylinder. The cylinder should come first and foremost.
A ball hone should only be used for freshening up or re-ringing a motor.
Be careful of "trick of the week" parts that claim to perform magic. They just don’t work.Just remember Kart Racing can make you moderately wealthy, if you start out filthy stinking rich

The Art of Design & Production

1998-08-20T16:06:00.000-04:00

By: Randy Amundsen Date: August 20, 1998

We probably have 20 calls a week from customers who are full of ideas and thoughts about designing or re-designing our products or someone else's product. Some have a brand new idea that they would like us to manufacture. We like to hear new ideas and sometimes we can react and sometimes not. Bringing a new idea to market is a very complex task and very time consuming.
Several months ago we received our first BlockZilla blocks and right away we saw the need for a better side cover and a market for it.
What do you do, you have no drawings, all you have is a shape.
The first thing we did was to mount the block on a rotary fixture in one of our Haas Machining Centers in a horizontal position with the crankcase opening up. The block had to be perfectly square with the table. Now we are not talking just close, but within tenths of thousandths.
Now the block can be digitized. This is a process of converting shape into numbers.
Using the crankshaft center line as the starting reference, the crankshaft bearing pocket, the camshaft bore, bolt holes and dowel pin holes are located. Now the inside of the casting, as well as the outside, must be traced taking readings every .100" in the straight areas and sometimes every .020" in the curvature areas. We now have pages of reference point measurements. This process takes about 6 hours.
These numbers are now transferred to a CAD system and a simple drawing is now created. From this, we now make a template side cover to test all the measurements. This is checked and rechecked for accuracy and how it fits the block. The crankshaft and camshaft must be installed and checked.
The process has been simple so far and now the time consuming work begins.
Designing is a true art form that takes a lot of talent, imagination and patience.
You must have a superb knowledge of what this part plays in the function of the engine. Are there improvements to be made over the original and other designs ? If so, will the improvements make the part better ? We ask for input from engine builders and our racing customers. Many hours are spent in round table discussions.
You first must address the structural integrity of the part. Where does it need to be strong and where can you remove metal to make it light ? After all of this is done, then you design in the cosmetic enhancements.
While you are working your way through this process, you are also selecting the tooling such as end mills, drills, taps etc., that you will need to do the different holes, cuts, pockets and contours. Your goal is minimum tool changes because this is time consuming in a production environment. This will cause you to re-think some of the shapes and modify the program.
This is a very time consuming process and one is sometimes tempted to cut the cosmetics a little short. If you have ever seen anything we produce, you know we don't cut anything short.
Holding fixtures are the next most important project. There is an old saying in this industry, "If You Can Hold It - You Can Make It". To hold a part in one position and finish the product is simple. To hold a part multiple times, in different positions, is another art form in itself. When a part is moved to a different fixture, it must be precise and sometimes the accuracy must be held in the tenths of thousandths.
Now the holding fixtures must not only be accurate, they must be durable enough to withstand production. Are we going to make 100, 1,000 or 10,000 or more of these parts ?
We are now ready to make our first part. This is done slowly so that each part of the program can be checked. Like it or not, there are errors and adjustments are made as we go.
We now have our first side cover and it must be evaluated on a test motor. After very extensive testing, we are now satisfied with the product.
We now enter the final stage of cosmetic programming. This is where spindle speeds and feed rates are adjusted and different tooling is experimented with.
The finished product must be free of tool marks and should have a polished look right out of the machining center.
Overall time for this project was about 1 month with at least 100 hours spent on computer design, programming and machine time. Hope you like the product.

By Design

1998-07-20T16:03:00.000-04:00

By: Carl AmundsenDate: July 20, 1998
ARC Racing, by design, will not be the first to the market place (at least not very often) with new, earth shattering ideas or products. We're not slow by any means, we just want to bring you, our customers, a well thought out product that has been thoroughly engineered and tested. We won't take an idea, make the part, then sell it to you for our testing purposes.
When we test a part, a motor is built and then run under the most undesirable conditions. We literally try to break it and, if we fail to break it, we try again.When testing the different alloys for our connecting rods, we even conducted the "Dirt Road Red Neck Test". This is done by taking rods of different designs and alloys and putting them in a vise and using a pipe to see how far they would bend before breaking, and we did break a few.
For the most part, when you buy an ARC Racing product it will be stronger, lighter and cosmetically more appealing than our competition offers and you'll be proud to own it.
We have never - and will never advertise that "this part will give you one more horsepower", or "this part will shave another seven tenths" and so on. The parts you buy from us are true racing parts and in the proper combination (with a little common sense) will make you go fast and, with a little luck added, maybe faster than everybody else.

Rod Length Ratios

1998-07-18T09:07:00.000-04:00

There are as many theories about rod lengths as there are any other subject that deals with racing.
As strokes get longer, rod lengths get shorter and at some point in time, this will create a problem. We don't know if we've crossed the line yet, but we're definitely leaning on it. At the same time, there's a point where rod lengths can get too long for a particular stroke and we're leaning on that line also.
Rod length ratios are calculated by dividing the rod length by the stroke.Example: a 5.000" rod length divided by a 3.000" stroke equals a 1.67 rod ratio.
For a good illustration of what increasing the rod length does for an engine, we'll use a 350 Chevy.A stock 5.7" rod divided by a stock 3.480" stroke gives us a 1.637 rod ratio.Now, put a 6.00" rod in it with the same stroke and the ratio increases to 1.724 and the engine produces more power and rpm.. This is a known fact that's been around for some 25 years.
A stock, 5 hp. Briggs & Stratton engine uses a 3.875" rod and has a 2.437" stroke which equals a 1.59 rod ratio.We know that by changing the rod to 4.475" and using the same stroke, the ratio increases to 1.863 and the engine produces more power and rpm.
The most important thing that a longer rod does is increase the dwell time of the piston when it's at top dead center (TDC) and this will make more power.The second most important thing is that it improves the leverage the piston exerts on the crank journal and this also increases power.
Another feature of using a longer rod is that it creates a much friendlier environment for the piston, cylinder and crankshaft to operate in.Consider this: The piston is moving up and down in the cylinder trying to make a crankshaft rotate in a circle. When the piston is in a down stroke, the resistance of the crankshaft is trying to push it out the front of the block and in an up stroke, with the resistance of compression, the crankshaft is trying to push it out the back of the block.Our recent test engine had a 4.225" rod with a 3.000" stroke equaling a 1.408 rod ratio and we believe we may have gone beyond the short rod ratio limit but, the engine made a bucket full of power and survived even at 9,300 rpm.
Rest assured that one day we'll reach the point of sheer stupidity.

What is Safe Peak Power RPM for an engine?

1998-07-18T09:05:00.000-04:00

This is a question that is rarely asked before an engine blows, but always asked after the second one is in a basket.
The formula is simple: divide 22,000 by the stroke.Why 22,000 you ask ?Well, the automotive industry came up with this number after decades of engineering research using literally hundreds of stroke lengths - and we believe it's probably correct.Example: The engine we just finished testing had a 3.000" stroke so 22,000 divided by 3 equals 7,333 safe peak power rpm (which we slightly exceeded for our test).
Now that you know - just keep on truckin.

The 10,000 rpm Bomb

1998-07-18T08:59:00.000-04:00

Several times a week we get calls from people that have just exploded their engine and, for the most part, they're looking for answers as to why it happened. On occasion, they'll send us some of the parts (or the whole mess) for evaluation hoping that we can shed some light on the problem. Well - sometimes we can and sometimes we can't.
Lets take a moment to consider where it all started and where we are now.We took a 5 hp. lawnmower motor that was designed to turn a maximum of 3,600 rpm then bored, stroked, welded, ground, filed, polished, fitted, crammed, invented and generally violated the entire book on common sense and ended up with a remanufactured 10,000 rpm BOMB and all of this was done in the name of fun. Well, of course it is.
We just finished testing an engine with a .174 overbore and 3.000" stroker crank and at 9,000 rpm this is what was happening inside that engine:1. The valves were opening and closing 150 times per second.2. The crankshaft rod journal was traveling 79.8 mph in a 3" diameter circle.3. The piston & rod moved, stopped then changed direction 18,000 times per minute (300 times per second).
Think about this:The piston is at top dead center (TDC) in a momentary stop position, we've already had combustion, the piston travels down the cylinder 1.3671" reaching a top speed of 84.3 mph. while the crankshaft has rotated 75° and all of this has only taken 1/720th of a second to happen.
Another way to look at it:The piston and rod start and stop 300 times per second reaching 84.3 mph. between each cycle.
Now, we ask the $ 64,000 question:Could anything go wrong in this kind of environment ?The answer is - Everything.It's truly an engineering miracle that this (or any) engine ever gets to 9,000 rpm just once let alone sustaining it.

Rod Length Ratios

1998-07-18T08:17:00.000-04:00

Discovery by Fatality

1998-07-08T17:06:00.000-04:00

Re: Crankshaft flex and side covers
By: Lynn Cooley Date: July 8, 1998

We all are aware that a crankshaft will flex and bend. What we don’t know, or should I say didn’t know, is how much. We also didn’t know what kind of specific problems the flexing would create.
Obviously the .875" journal crank could flex more than the 1.000" journal crank but there is not as much difference as you might think.

As a lot of you already know, we have been conducting tests on our new .875" stroker rods. This has been ongoing for about 6 months and we've tried several engineering designs along with different alloys and finally arrived at the ultimate design and alloy. Now let the serious testing begin.
We have a dynamometer but felt that real testing is accomplished on our adult fitted Jr. Dragster and a custom built Kart.

Our first test engine was built using a Raptor block, .140" overbore, 4.225" ARC stroker rod with .875" bearing, 3.000" forged stroker crankshaft, ARC head, ARC flywheel and ARC billet side cover.
This engine assembly was carefully balanced by us.

Now, to be fair and honest, our goal from the get go was to break the rod. We really abused this engine. Our RPM limit was 9000, but we did hit 9300 a couple of times.
The first problem was a high RPM miss and then coil failure. The clearance between the flywheel and the coil was set at .020. When the flywheel rubs the coil the first thing that happens is an interruption of the magnetic field and the coil misfires. The next thing is that friction creates heat and fries the coil.

The flywheel was checked and was running true and the coil was not slipping on its mount. We finally had to set the air gap on the coil at .030 to keep it from contacting the flywheel. This seemed strange and, little did we know, our next lesson would teach us a lot.
About 10 more minutes on the Kart and we blew that sucker all to pieces. The only parts that survived were the carburetor and the ARC cylinder head. The ARC stroker rod looked like it had been through a war but survived - unbroken.
The crankshaft had broken straight down at the radius of the rod journal. This is exactly were it would and should break if the crankshaft bends and flexes. Incidentally this crankshaft is one of, if not the best on the market.

The first symptom of this flex problem was the high speed miss and then the coil failure. By examining where the flywheel had rubbed the coil the hardest, we determined that most of the flex occurs at BDC (bottom dead center). The second place was just after combustion or TDC (top dead center), both of which really make sense.

Think about it - cylinder pressure is at its highest just after combustion and when the piston reaches the bottom, there is no resistance to cushion the abrupt change in direction of the reciprocating weight. As the piston travels upward, it has compression to offer resistance in one stroke and exhaust gases to offer some shock absorption on the next.
On the same note, have you ever wondered why additional deck clearance is needed the more you increase engine RPM? Most engine builders think of rod stretch the same as you do in automotive.
In a Briggs application, crankshaft flex is the main problem. In fact, we checked every rod we had tested and didn't find any permanent stretch.

Our next test engine was built using a BlockZilla block, .174" overbore, 4.225" ARC stroker rod with .875" bearing, 3.000" forged stroker crankshaft, the new ARC BlockZilla head, ARC flywheel and a billet side cover (no name mentioned). The ARC side cover was still working its way through engineering.

With the air gap set at .030" between the coil and the flywheel, we ran the engine very hard for 10 minutes, stopped and immediately tore it down. The temperature of the crankshaft got our attention real fast. After 45 minutes the crank was still to hot to handle (have you ever bent a piece of wire back and forth and felt the temperature just before it broke?). We felt that if we had run it any longer, we would have broken another crankshaft.

One other problem that showed itself on the billet side cover (no name mentioned) was that the 0-ring seal had scuffed and chaffed itself almost into nonexistence along the top of the cover. Along the bottom and up each side seemed to be OK (remember, this was only a 10 minute run).

THE PROBLEM
Ball bearings, by nature, have a certain degree of self-alignment built in. The inside dimension between the 2 ball bearings in the block is 3 ½ inches. It's not hard to flex the shaft .020" in one direction and still have a free spinning shaft. This translates to at least .040" total flex in the shaft and could probably go to as high as .050" and still free spin.
To add insult to injury, the manufacturer of the forged cranks we tested leaves entirely to much clearance on the slip fit bearing area on the shaft. This dimension should be .9995" not .998". This sloppy fit can allow another .015" flex and still free spin. Remember this lesson if you ever have to slip fit a bearing on a stock Briggs crankshaft.

To summarize all of this, it's no wonder the flywheel rubbed the coil and that the crankshaft broke.

THE SOLUTION
Since the ARC BlockZilla side cover was still in the engineering stage, we added a second ball bearing to it and held them in place with 3 recessed button head screws. This created the first DUAL BEARING SIDE COVER.

After installing our new duplex bearing side cover on the same BlockZilla block with .018 clearance between the coil and the flywheel, we had no problems. The engine was run hard for 20 minutes then disassembled and with a shorter cool down period, the crankshaft was noticeably cooler. This was a huge improvement even though the crankshaft had the sloppy slip fit on the bearings.

One other plus over the (no name mentioned) side cover that we tested, is that the ARC BlockZilla side cover is truly light weight, and the ribbing supports on the outside of the cover and, more importantly, the outer perimeter ribbing reduce flex.
Our 0-ring seal showed just a slight sign of scuffing.

The testing was so successful, we decided to use this same technology on our Raptor side covers, and they will be available by the time you read this.
You should see a longer life of the Raptor blocks as well.

The primary reason for all of this testing was to see if our new stroker rod design would live, and IT DID. Both sizes are now in production and available.

See our "Product Showcase" for details of these and other new products.

SPECIAL NOTE:
We try very hard to keep our prices competitive, so look closely at what is furnished with this new ARC side cover design :)

Remove 400 lbs. from your crankshaft!

1998-07-02T08:34:00.000-04:00

How - you ask ? With an ARC billet connecting rod.Compared to some connecting rods that are on the market today, the ARC rod produces 400 lbs. less centrifugal force (on the crank journal end) at 9000 rpm.That's a lot of unnecessary pressure on the rod, rod bolts, bearings and crankshaft.
Have you ever wondered why additional clearance is needed in the air gap between the coil and flywheel and piston to head clearance on a high rpm race engine ? Crankshaft flex !The less weight the crank rod journal "feels" the less flexing, fatigue, wear and breakage you'll encounter.
How can a part be lighter, smaller and stronger ?After numerous hours of research into the physical properties, force, inertia, elasticity and extensive dyno pulls of connecting rods, we found that attention to details such as shape, type of material, size and weight are extremely important to the structural integrity of a connecting rod.
Just one more plus of the ARC billet connecting rod is that when it's used with most Briggs & Stratton crankshafts, the engine is better balanced. This is very important for the Kart classes that don't allow modifications to the crankshaft :)