K1 - Tech
Checking and setting proper crankshaft end play is a vital engine-building step. We show you how to do the job in this tech segment.
Engine building isn’t difficult – as long as everything goes according to plan. The challenge for the engine builder is to anticipate problems before they occur. Much of the process of becoming a successful engine builder is checking all the clearances and custom setting them when they are out of tolerance.
Crankshafts are generally among the most abused components in an engine. One way to minimize this abuse and maximize the crankshaft’s opportunity to deliver a long service life is to make sure all the clearances are correct. For this story, we’ll be looking at thrust clearance or what is often called end play. This is the amount of clearance between the crankshaft’s thrust plate and the vertical surface of the main thrust bearing.
It’s worthwhile to discuss first why it’s important to have a thrust bearing. There are transmission loads that tend to force the crankshaft forward. With automatic transmissions, this can originate from the torque converter. This should never exceed a light forward pressure, but this load does exist and must be accommodated.
Crankshaft End Play
0.003 - 0.011
0.006 - 0.010
GM LS Gen III / IV
0.004 - 0.008
429 – 460 Ford
0.004 - 0.008
Ford Modular 5.0L
0.004 - 0.008
340 – 360 Mopar
0.002 - 0.007
0.003 - 0.007
Mopar Gen III hemi
0.002 - 0.011
Ideal clearance would be mid-point between these minimum and maximum clearances.
Manual transmission thrust can be excessive with pressure plates that generate high static loads. The most abusive of these are the three-finger style pressure plates that use internal coil springs. With the clutch pedal on the floor, a major portion of the load released by the clutch pedal is directed forward into the crankshaft. These pressure plates are most often used in race engines, explaining why it’s always best to start an engine with the transmission in neutral so that the crank spins with no forward load. Starting a cold engine (when most of the oil has drained from this area) with the clutch pedal on the floor places tremendous load on the thrust bearing. It’s best to avoid this by starting the engine with the transmission in neutral.
For this checking example, we will be using a K1 steel crankshaft in a Dart Little M cast iron small-block Chevy. It’s always best to test fit all clearances for a new engine before final installation in case modifications are necessary. For this application, we pre-assembled the rear main thrust along with the Number One main bearing, dropped in the crankshaft, and installed the main caps with the studs lightly tightened.
Before fully torquing the main studs, it’s necessary to align the two pieces of the thrust bearing. To do this lightly hit on the rear of the crank with a rubber or plastic mallet. This will ensure the thrust surfaces are even from the rear which is where all the force will originate. This ensures the paired bearings are parallel. With this accomplished, the main caps can be torqued to the proper spec.
Next, you will need a magnetic base and dial indicator. Align the dial indicator plunger parallel to the crank snout and lightly force the crank backward and zero the dial indicator. Now lightly force the crank forward and read the amount of movement on the dial indicator. Different engines demand varying specs. Generally speaking, keeping the thrust clearance at 0.004 to 0.005-inch is appropriate but it is best to check the recommended clearance. For example, late model engines prefer a slightly tighter clearance to minimize travel of the crank sensor reluctor wheel. We’ve included a chart listing factory endplay dimensions for some of the more popular performance engines.
If when assembling an engine you discover the clearance to be very tight, there is a simple way to increase the clearance. The generally accepted procedure is to clamp the two thrust bearings together with a hose clamp, making sure the thrust surfaces are aligned and flat. Also make sure the two halves are clamped as they sit in the engine – it’s possible to orient them incorrectly which will not produce the results you desire. Always position the two halves with the locating notches facing each other. Then place a full size sheet of 600-grit wet/dry sandpaper on a large plate of either plate glass or flat metal plate. Add a few drops of machine oil like Marvel Mystery oil to the sandpaper.
It’s best to sand only the leading edge side of the thrust bearing when increasing clearance. This way, the thickest portion will be the trailing side which is where any wear will occur. Measure the combined width of the thrust bearing across both wear surfaces with either a quality dial caliper or a micrometer. We generally see a slight difference in thickness of perhaps 0.001-inch across the thrust bearing face.
Record this dimension and then keep sanding until you gain the necessary clearance. Generally you may need to only increase the clearance by 0.002- or 0.003-inch, but you will be surprised at how much sanding this will require. Some engine builders will lightly dress the sanded face with 1000 grit paper to polish the surface once the proper clearance is achieved. Of course, a thorough cleaning with hot soapy water and a sponge followed by a wipe-down with rubbing alcohol and a white paper towel is necessary to ensure that all of the sanding grit is removed before the bearing is re-inserted into the engine to recheck the clearance.
Crankshafts that are discovered suffering from excessive thrust clearance are rare, assuming no damage has occurred to the crankshaft. Alternatives may be to try a different bearing manufacturer to see if the clearance will improve although this is unlikely. The only other solution is to have the crankshaft repaired to put the thrust thickness back to its stock thickness. This may cost nearly as much as the price of a new crankshaft.
Checking and setting clearances is all about stacking the longevity odds in your favor. The payoff is when that engine starts and runs properly and delivers a long, productive, and powerful life.
Verifying and adjusting bearing clearance is one of the most critical aspects of building an engine. In this segment, we dive into the mechanics of how to measure your crank, connecting rods, and bearings.The simple fact is that setting bearing clearance for a performance engine is something that cannot be short cut. There are no quick and easy ways to establish this critical clearance regardless whether the engine is a bone-stock cruiser or a road course animal that will endure hundreds of miles of abuse.
We will run through the basics on how to measure bearing clearance and illustrate how to avoid mistakes. This will also require some critical measuring tools. Let’s just put this right out front – measuring bearing clearance for a performance engine cannot be accomplished with Plastigage. Those little pieces of wax thread are not precision measurement dev
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It seems every day that there is a new post on social media about street engines making four-digit power. A killer late model Hemi with a blower easily pushes past 1,100 horsepower and Mike Moran has built an all-billet, twin-turbo engine that made 5,300 horsepower. The power numbers keep escalating and yet far less attention is paid to what it takes for crankshafts, pistons, and connecting rods to survive these ever-escalating, and easier-than-ever-to-achieve power levels.
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It’s all part of the art of building a performance or competition engine. The details separate the exceptional from the also-rans. Some specs like rod and main bearings receive a majority of the attention, but ignore something as simple as deck height and you could find a piston smacking the head at high rpm is not a good way for reciprocating parts to become acquainted.
This really isn’t a critical dimension if a standard rebuild is the goal. But if you’re a performance engine builder and stroker cranks, longer rods, shaved decks, and custom pistons are your thing – then block deck height is an important dimension that demands attention. For the record, deck height is the distance between crankshaft centerline and the top of the block.
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Our friends at Moto IQ show you how to build a Coyote engine within your budget!
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Small changes offer big benefits when it comes to selecting aftermarket rods for your next Chevy LS engine build. Here’s a look at how rod length affects the performance and durability of an engine - and you thought you’d never use that Geometry you learned in high school!27 thousandths of an inch doesn’t sound like much. It’s about the thickness of a multi-layer steel head gasket typical for 4 cylinder applications. It’s almost exactly half as thick as a dime, which mics out at 0.053 inches. It’s a bit smaller than you might gap your plugs on an old-school points ignition small block Chevy. But like everything involved in high performance engine building, tiny fractions of an inch make significant differences in horsepower and durability, and that’s why rods that are ever so slightly longer than “factory stock” have become a big deal in LS engine builds.
An intense look at crankshaft stroke and its affect on mean piston speed, inertia, and controlling the massive, destructive forces at work inside an engine.Engine builders have long calculated the mean piston speed of their engines to help identify a possible power loss and risky RPM limits. This math exercise has been especially important when increasing total displacement with a stroker crankshaft, because the mean piston speed will increase when compared to the standard stroke running at the same RPM.
But what if there was another engine dynamic that could give builders a better insight into the durability of the reciprocating assembly?The video above shows two engines, one with a short stroke crankshaft, and the other with a considerably longer stroke. Note that both pistons reach top dead center and bottom dead center at the same time, but the piston in the longer stroke engine (left) has to move significantly faster.
â€œRather than focus on mean piston speed, look at the effect of inertia force on the piston,â€ suggests Dave Fussner, head of research and development at K1 Technologies.
Letâ€™s first review the definition of mean piston speed, also called the average piston speed. Itâ€™s the effective distance a piston travels in a given unit of time, and itâ€™s usually expressed in feet per minute (fpm) for comparison purposes. The standard mathematical equation is rather basic:
Mean Piston Speed (fpm)=(Stroke x 2 x RPM)/12
Thereâ€™s a simpler formula, but more on the math later. A pistonâ€™s velocity constantly changes as it moves from top dead center (TDC) to bottom dead center (BDC) and back to TDC during one revolution of the crankshaft. At TDC and BDC, the speed is 0 fpm, and at some point during both the downstroke and upstroke it will accelerate to a maximum velocity before decelerating and returning to 0 fpm.
There are formulas to calculate the piston speed at every degree of crankshaft rotation, but thatâ€™s usually much more information than needed by most engine builders. Traditionally they look at the average or mean piston speed during the crank rotation, and they possibly will calculate the maximum piston speed.
The mean piston speed takes the total distance the piston travels during one complete crankshaft revolution and multiplies that by the engine RPM. Piston speed obviously increases as the RPM increase, and piston speed also increases as the stroke increases. Letâ€™s look at a quick example.
A big-block Chevy with a 4.000-inch-stroke crankshaft running at 6,500 rpm has mean piston speed of 4,333 fpm. Letâ€™s review the formula again used to calculate this result. Multiply the stroke times 2 and then multiply that figure by the RPM. That will give you the total number inches the piston traveled in one minute. In this case, the formula is 4 (stroke) x 2 x 6,500 (RPM), which equals 52,000 inches. To read this in feet per minute, divide by 12. Hereâ€™s the complete formula:
(4 x 2 x 6,500)/12=4,333 fpm
You can simplify the formula with a little math trick. Divide the numerator and denominator in this equation by 2, and youâ€™ll get the same answer. In other words, multiply the stroke by the RPM, then divide by 6.
(4 x 6,500)/6=4,333 fpm
With this simpler formula, weâ€™ll calculate the mean piston speed with the stroke increased to 4.500 inch.
(4.5 x 6,500)/6=4,875 fpm
As you can see, the mean piston speed increased nearly 13 percent even though the RPM didnâ€™t change.
Again, this is the average speed of the piston over the entire stroke. To calculate the maximum speed a piston reaches during the stroke requires a bit more calculus as well as the connecting rod length and the rod angularity respective to crankshaft position. There are online calculators that will compute the exact piston speed at any given crankshaft rotation, but hereâ€™s a basic formula that engine builders have often used that doesnâ€™t require rod length:
Maximum Piston Speed (fpm)=((Stroke x Ï€)/12)x RPM
Letâ€™s calculate the maximum piston speed for our stroker BBC:
((4.5 x 3.1416)/12)x 6,500=7,658 fpm
By converting feet per minute to miles per hour (1 fpm = 0.011364 mph), this piston goes from 0 to 87 mph in about two inches, then and back to zero within the remaining space of a 4.5-inch deep cylinder. Now consider that a BBC piston weighs about 1.3 pounds, and you can get an idea of the tremendous forces placed on the crankshaft, connecting rod and wrist pinâ€”which is why Fussner suggests looking at the inertia force.
â€œInertia is the property of matter that causes it to resist any change in its motion,â€ explains Fussner. â€œThis principle of physics is especially important in the design of pistons for high-performance applications.â€
The force of inertia is a function of mass times acceleration, and the magnitude of these forces increases as the square of the engine speed. In other words, if you double the engine speed from 3,000 to 6,000 rpm, the forces acting on the piston donâ€™t doubleâ€”they quadruple.
â€œOnce started on its way up the cylinder, the piston with its related components attempt to keep going,â€ reminds Fussner. â€œIts motion is arrested and immediately reversed only by the action of the connecting rod and the momentum of the crankshaft.â€
Due to rod angularityâ€”which is affected by connecting rod length and engine strokeâ€”the piston doesnâ€™t reach its maximum upward or downward velocity until about 76 degrees before and after TDC with the exact positions depending on the rod-length-to-stroke ratio,â€ says Fussner.
â€œThis means the piston has about 152 degrees of crank rotation to get from maximum speed down to zero and back to maximum speed during the upper half of the stroke. And then about 208 degrees to go through the same sequence during the lower half of the stroke. The upward inertia force is therefore greater than the downward inertia force.â€
If you donâ€™t consider the connecting rod, thereâ€™s a formula for calculating the primary inertia force:
0.0000142 x Piston Weight (lb) x RPM2 x Stroke (in) = Inertia Force
The piston weight includes the rings, pin and retainers. Letâ€™s look at a simple example of a single-cylinder engine with a 3.000-inch stroke (same as a 283ci and 302ci Chevy small-block) and a 1.000-pound (453.5 grams) piston assembly running at 6,000 rpm:
0.0000142 x 1 x 6,000 x 6,000 x 3 = 1,534 lbs
With some additional math using the rod length and stroke, a correction factor can be obtained to improve the accuracy of the inertia force results.
Crank RadiusÃ·Rod Lenth
â€œBecause of the effect of the connecting rod, the force requi