Hi, I'm going to have a go at a marine engine for my next project. http://www.john-tom.com/MyPlans/Steam Engines/MarineEngine.pdf In the past I have made the pistons from phosphor bronze with a couple of fine grooves cut into them to retain oil. I was watching Keith Appleton on Youtube () and he used silicone piston rings to repair an old engine. I would like to use the same system for the marine engine but I'm not sure how to implement it. The plans call for a 1" piston but I think I'll probably go for 3/4". Are silicone piston rings just ordinary silicone O rings with the standard clearances normally associated with O rings? If so, what wall thickness would be appropriate for a 3/4" bore? On the Keith Appleton video it looks to be about 1/8". Regards, Alan C.