A couple of years ago I built a Snow engine and had it running fairly well. Recently I have been going back to past builds and trying to get them to run better. The Snow had rather poor compression after setting so I ended up making some new rings and trying some other things. When I put compressed air (20-30 PSI) into the cylinders everything seems to seal and have minimal leaks. When I turn it over by hand it does not seem to generate much compression. I finally came to the conclusion the the garter spring seals were expanding when enough pressure was applied but not sealing at lower pressure. I am thinking about trying string packing similar to what I would use in a steam engine.