Randy , one of the ST60's that I have in my stash was bought in a disassmebled state. I think the back cover is not the correct one for this engine as it does not have the flat area to provide clearance for the rear of the piston skirt at BDC (all my other ST60's have this flat area). Any problem with me just milling the skirt of the piston for this clearace? Not sure what the rear cover came off of but it seems to be correct except for the flat area missing.

HI Gordon
You can do that but need to be very careful that there is enough material, You may have one for an older 51 and some of those do not have enough al  to mill a flat, Also some had different depths that plugged in, so you need to check that too

Randy

Don't mill the skirt. It's unlikely that there is enough material to avoid uncovering the bottom of the exhaust port at TDC. Mod the backplate.

Found another ST60 in the stash. Early model with no ears and two rings, tall head. The piston is cut front and back and will clear the back cover. I swaped rear covers and everthing clears but I still need to check total clearance from back of rod/crank pin to inner face of rear cover. Now here is something else I have noticed I was checking my Bristunt P/L sets for these ST60 engines , both P/L sets have the bottom of the pistons notched front and rear like the two ring piston. Have not assembled the Bristunts into case yet to check to see if there is any sub piston induction going on. Will put one in this early case , measure and check every thing and run it. Been wanting to try one of these Bristunts for awhile. If it runs good I will try to Tig on some muffler ears to the case. I will practice on a busted up 46 case I have to get the process proved. Don't won't to ruin a ST 60 case.