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Old 05-05-2017, 02:00 PM   #11
Wayne Kerr
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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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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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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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Old 06-09-2017, 07:54 PM   #14
Jim Hanig
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Default Re: wrist pin clip issues

Quote:
Originally Posted by Wayne Kerr View Post
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
Wayne what is časy best way to check this..? Thanks
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Old 06-12-2017, 11:04 AM   #15
Charlie Yannetti
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Default Re: wrist pin clip issues

Simple question.. how much vacuum are you pulling??.. too much vacuum will affect oiling to the wrist pins, and possible damage... just an idea..
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Old 06-23-2017, 10:52 AM   #16
Wayne Kerr
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Default Re: wrist pin clip issues

Just use a regular one inch travel dial indicator, with an extension. Welding rod for the extension will suffice.

See you at the races,
Wayne Kerr
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Old 09-08-2017, 09:48 AM   #17
Adger Smith
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Default Re: wrist pin clip issues

Wayne,
I'm not squirming or pissing and moaning. I agree with you on clearance, but too much makes the pin act like a battering ram on the clips. most applications I deal with .002 to .006 is plenty. But first Get the alky tune up correct where it won't flood when the driver is pedaling it and the pistons and pins won't deflect so much they need more clearance. I do agree pins need end play, but most pistons grow outward at the pin boss when the engine heats up making more pin end play. Flooding it with the alky is probably keeping piston temp down = no piston growth & more deflection of the pin and piston. I have seen the very same thing in Dirt engines with 4" bores. It bothers me to see a driver that has abusive habits. Some times those DT cars have drivers that are real harsh with the loud pedal, too.
There could be multiple issues with this one. It could even be a set of pins that are not up to handling the load the alky puts on them. Pin deflection can be a real serious issue on high cylinder pressure applications. Good luck fixing it.
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