rearenginekarts.com

I am rebuilding a mac 20 motor and i am going .030 over on the bore,my machine shop needs to know the piston to cylinder wall clearance, and the correct ring gap to use? any help would be appreciated, Thanks Bob Mosher

Robert, a good running piston skirt-to-cylinder wall clearance is .006 to .0075. Ring gap from .007 to .040 (even more is O.K.). I try for about .015 ring gap on a gas burner, as they run hotter and the rings expand more than an alky burner. This is assuming that your piston does not have anti-rotation pins. If it has an anti-rotation pin coming vertically through the piston crown (like early Wiseco), you have to notch the rings at the backside of the ends at the gap to surround the pin. Make sure the rings don't bind on the pin when they're in the bore. If your piston is pinned through the ring lands from the piston wall, add the pin diameter to the end gap listed above. Ring gap on the high side doesn't hurt performance.