Just happen to be working on a 499cc and a 795cc engine at the same time. I had the bits on my table and thought that the Piston comparison made an interesting picture
After a major struggle to find some new piston rings for the Italian made ASSO 85mm pistons I finally came up trumps and set about fitting them today. ASSO still make Pistons but did not answer my inquiry as I think they only make scooter ones now. Gave the Pistons a final clean then noticed that on the inside there a four curved steel plates set into the wall. Not seen anything like it before.