wrist pin clip issues

[Todd Gross]

I had one customers' engine that I tore down for a freshen up only to find multiple spiro loc failures. To the point of serious cylinder wall and piston damage. After digging for info I found out the previous assembler purchased his spiro locs in bulk from McMaster Carr. Needless to say the quality control ( heat treat ) may not be up to the quality of that of a Performance Piston company. I installed JE locks and 2 seasons later on freshen up, no more failures on a 700" .
I am not suggesting that that toolmakeron's engine has McMaster stuff in it, just sharing an experience*

[Wayne Kerr]

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

[Jeff Stout]

Originally Posted by Wayne Kerr

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

[Wayne Kerr]

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

[Jim Hanig]

Originally Posted by Wayne Kerr

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 èasy best way to check this..? Thanks

[Charlie Yannetti]

Simple question.. how much vacuum are you pulling??.. too much vacuum will affect oiling to the wrist pins, and possible damage... just an idea..

[Wayne Kerr]

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