piston skimming for stock(ish) width engine

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piston skimming for stock(ish) width engine

Post by '61crewcab » Sat Nov 25, 2017 7:37 am

Is there a 'safe' limit that pistons can be skimmed? I'm building a 74 x 90.5 with a W100 cam, and to get my CR correct and maintain a 1.1mm deck height, I will need to use 2.6mm barrel to case spacers. I'd like to get an off the shelf exhaust, so don't want to widen the engine anymore than I have to. My aim is to skim the pistons and use thinner spacers. The engine is for a truck. thanks

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Re: piston skimming for stock(ish) width engine

Post by Marc » Mon Nov 27, 2017 1:55 am

FWIW, I used to notch Cima/Mahle 90.5A cast pistons for valve clearance up to .120" deep and never had a failure (and that was in pretty extreme service, too). I'd suppose you could safely take 2mm off the whole crown with no worries, that'd bring the engine width back to where the exhaust and shroud should fit without issues. If yours are AA pistons I couldn't say - haven't sawed any of those apart to see their crown thickness yet.

Chopping down the crown narrows the top ring land and exposes the top ring to more heat. I've run Berg's 88Bs which were made by cutting down an unfinished casting for a higher effective pin height, their top land was quite a bit narrower than stock (don't recall off the top of my head just how narrow but I can dig some out and measure that tomorrow - pretty sure they're chopped down by at least 4mm though)...didn't ever experience a problem with those so again you should be OK at ~2mm.

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