Piston side wall clearance???

[81vette]

My SRP "Forged High Silicon" pistons call for a .002-.0025 side wall clearance on street cars. The card from SRP says this clearance is built into the pistons, however my measurements only confirm that 4 of the pistons have this built in tolerance for my 4.1555 bore. I've listed the piston skirt measurements below for all 8 pistons (measured multiple times and at the correct skirt location). I guess my question would be is this range typical of all pistons or just the SRP pistons? 4.1531 4.1531 4.1532 4.1535 4.1539 4.1539 4.1539 4.1547 Mark

[CFI-EFI]

I don't know if the deviation you have displayed is "typical" or not. I DO
know that final cylinder finishing and sizing SHOULD only be done with the
pistons on hand so the machine shop can "precision" fit the pistons to each cylinder.

RACE ON!!!

[Twin_Turbo]

I agree w/ CFI-EFI. Have your machine shop custom fit (and make tolerance) for each piston, no 2 pistons will be exactly the same.

Marck

[427Hotrod]

Mine had about .0025 built into them. I wanted them at .0045, so we put her back on the hone 'till it was right.

The SRP's are designed to be able to run a little tighter than normal forged ones, but I preferred a little looser.

Just as a side note, they are dead quiet even on cold start-up in the 540.

JIM

[clem zahrobsky]

SRP is(was) part of JE and GM bought JE a special compuer controled milling machine to do the 502 marine pistons for GM. that is why they are such close fit because of the shape. i have use JE pistons in a 4 cylinder race engine with a 3.500 bore and fit them at .0015. :chevy

[arnold]

My SRP "Forged High Silicon" pistons call for a .002-.0025 side wall clearance on street cars. The card from SRP says this clearance is built into the pistons, however my measurements only confirm that 4 of the pistons have this built in tolerance for my 4.1555 bore. I guess my question would be is this range typical of all pistons or just the SRP pistons?Mark

I'll tell you of one condition. You tell me who the good looking 'guy' is, that is taking center stage in front of the vette. :)

Ah, don't know what is correct/normal, can just tell you what I noted. My SRPs varied .0002-.0003".

Mine had about .0025 built into them. I wanted them at .0045, so we put her back on the hone 'till it was right.
The SRP's are designed to be able to run a little tighter than normal forged ones, but I preferred a little looser.

I consider that a 'gutsy' call, to overrule factory engineering. Those guys have undoubtedly done their homework. What is 'built' into them is just a side note. Bottom line, actual clearance machined.

Just as a side note, they are dead quiet even on cold start-up in the 540.

It is nice to know, there is SOME tolerance to looseness. :)

SRP is(was) part of JE and GM bought JE a special compuer controled milling machine to do the 502 marine pistons for GM. that is why they are such close fit because of the shape. i have use JE pistons in a 4 cylinder race engine with a 3.500 bore and fit them at .0015.

I was led to believe the tite fit is due to the lack of expasion from the high silicone content. :confused:

[81vette]

That's my son Arnold. Thanks for the kind words. :)

Thanks for all the replies. The variance of this set of pistons is greater than I expected. They should all have been around 4.1528 +- .0002, but maybe I'm expecting too much. So far everything else looks good. I think I'll call SRP to see if this variance is normal in their pistons.

Mark