Well the first one is done anyway. The Stihl 640 piston ended up working real well, at least after the pin bosses were widened for it to fit over the rod. Like I said my crude measurements showed it to be .022" taller then the stock piston. When installed on the saw it ended up with .028 squish. I used the original base gasket that was in good shape and stuck tight to the case and put a little hylomar on it for good measure. While it was apart the saw got new crank seals, impusle line, fuel lines and carb kit. My compression tester has been giving me trouble so I can't give the exact compression, but lets just say when you go to pull the rope, you better pull it like you mean it. It was raining pretty hard this afternoon so I couldnt put it in any wood yet but with the little bit of opening the muffler outlet, it has a real bark to it and seems really strong. Looks like I'll probably go ahead and rebuild the other one sometime since this one seemed to work out pretty well. Need to find a couple of things for it though. Here it is. It don't weigh quite what I thought it would either, in fact it was just a hair more then the MS460 that I weighed today.