Doe's anyone know where I can purchase a stock 38.8 MM piston and rings for my Minarelli V1 eng. I ordered a set of rings from HandyBikes but they dont fit. The diameter is right but they are too thick for the ring groove in piston. They were supposed to be Mfg. by Minarelli but I don't think so. Nothing has been changed on this engine. It is all stock from 1979. Help!