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Old 05-05-2017, 02:00 PM   #11
Wayne Kerr
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Join Date: Nov 2003
Location: Out to Lunch
Posts: 155
Unhappy Re: wrist pin clip issues

Ron,
You are going to have to trust me on this, and all the "experts" on here are going to piss and moan.
You need to have more pin end play. The reason the other engine opened up to .035" is because that's what it wanted. The pistons deflect from gas pressure and the pin bosses flex inward. We built a fixture and we put 1500 psi nitrogen on top of a room temperature piston just to prove this fact. Lost numerous cup engines and a few IRL engines as well, with too tight of wristpin end play.
Wristpin end play is like bearing clearance, too much and you know about it, too little and everybody knows about it.

See you at the races,
Wayne Kerr
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Old 05-05-2017, 04:04 PM   #12
Jeff Stout
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Join Date: Dec 2001
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Default Re: wrist pin clip issues

Quote:
Originally Posted by Wayne Kerr View Post
Ron,
You are going to have to trust me on this, and all the "experts" on here are going to piss and moan.
You need to have more pin end play. The reason the other engine opened up to .035" is because that's what it wanted. The pistons deflect from gas pressure and the pin bosses flex inward. We built a fixture and we put 1500 psi nitrogen on top of a room temperature piston just to prove this fact. Lost numerous cup engines and a few IRL engines as well, with too tight of wristpin end play.
Wristpin end play is like bearing clearance, too much and you know about it, too little and everybody knows about it.

See you at the races,
Wayne Kerr
What would be the desired amount of end play on a medium performance engine 150 wall 153 gram, and 545 gram piston, 3.385 stroke? I have .027 right now

Last edited by Jeff Stout; 05-05-2017 at 04:04 PM. Reason: more
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Old 05-08-2017, 07:48 AM   #13
Wayne Kerr
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Join Date: Nov 2003
Location: Out to Lunch
Posts: 155
Default Re: wrist pin clip issues

Good morning Jeff,
There are certainly many factors that are in play here. The first is piston design, the new "Box bridge design" pistons are reinforced in the pin boss area and can run less wristpin end clearance. .025" would be adequate for that type of piston while the old full round pistons like a Venolia, I would like to see .040"+
Bore size will play a role as well, bigger bore, more piston deflection.

See you at the races,
Wayne Kerr
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