I am building a 280 engine. How much clearance do I need in the piston for the wrist pins? (I have floated the rod/wristpins) One piston seems really tight with the wrist pin clearance being marginal. Will I need to relieve that piston so it is like the others? Or, as long as it pushes into the piston will it be OK?

Hi Loren,

Cast pistons will do fine with .0005. Forged pistons like .0008. the rods also need .0008, if they're bushed or not. You can guesstimate the .0005 by having a pefectly clean pin bore and pin, with some WD40 on the pin and bore the pin will just slip through by its own weight when you hold it upright. The old Mercedes needed .0012/.0015 cause the driver was always over reving it.

Phred

Thank you Phred. I do remember breaking a piston at Sears Point. I was trying to get all the way down the hill in 4th gear. I remember it started to rattle and I shut her down. Then you guys built the killer dual 4 bbl engine. That thing would rev to 9,000 when I needed it. Those were the days....