Having built the engine three years ago I got it to fire but never run .Now I am trying again I am thinkinking of viton o rings instead of piston rings.The bore is 38.2mm and I have found an o ring from Bearing Boys of an outside diameter of 38.4-34.5 internal and2mm cross section.would this ring be the right size and would one ring be sufficient,If ok what would the size of the groove be.