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
Tuesday, February 8, 2000
Tuesday, January 18, 2000
The Jury is Back and the Verdict is In
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.
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.
Tuesday, June 1, 1999
Probable Cause of Most Rod Failures
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.
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.
Thursday, January 7, 1999
The Crankcase Vacuum System (CVS)
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.
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
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.
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.
Wednesday, November 11, 1998
Stock Briggs & Stratton 5 hp.Calculation Formulas
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
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.
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
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
Thursday, August 20, 1998
The Art of Design & Production
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.
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.
Monday, July 20, 1998
By Design
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.
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.
Saturday, July 18, 1998
Rod Length Ratios
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.
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.
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