Ferrous_Head wrote:If your using stock pistons go with what the manual says. But there is a huge difference between what most cast piston and forged pistons run. This will (as I understand it) relate to the silicon content.) But in any case I would ask Wiseco for their recommendation.
I think the ultimate piston fit for the subject forged piston relates to several critical variables, e.g., the aluminum alloy (in this case 2618), the piston style (cam ground, barrel shape, or modern CNC hybrid design), the cylinder material, cooling, and end use (putting around or riding it like you stole it).
I looked back through some old notes I made and see that Wiseco recommended fitting at 0.0025”, Enfield recommended 0.0035 – 0.004” and the race engine builder who recommended 0.004-0.0045” (I misquoted this earlier when I said this was Enfield’s recommendation). I would never think of running this forged piston at the Wiseco recommendation of 0.0025”, because Wiseco lacks experience with this particular engine design, it’s intended end-use and it’s operating temp. I guess the only way to really know the lower limit of fit is to start snugging them in and determine at what point things start to tighten up (but that doesn't sound like much fun to me).
For what it’s worth, the Wiseco part# for the ring pack is encoded to provide the nominal ring size. In my particular case of 0.060” OS pistons the ring pack part # is 2815XC, so the nominal ring dia is 2.815”, and the piston, at it’s largest dia is ~ 0.002 -0.003” smaller than this, so all in all completely consistent with the Wiseco recommended fit.