I bought a never been run Enya 35 Model 5224 recently. This is the engine that comes with the hi and low compression heads and 3 different size venturies. I have about an hour on the engine with the low compression head and small venturi. It seems to be getting tighter the more I run it. It does not flip freely like a normal engine. I've broken two 9 x6 props lately from fliping it to start it. Also, it gets real hot running a rich four cycle. I'm bench running it using 10% nitro 26% castor with 2% syn. to make a total of 28% oil fuel. I would not normally disassemble an engine but I took the front of the crankcase off and checked the rotation of the crank. Nice and free. Now being a Machnist/ Tool and Die Maker for 30 years, I do know something about what kind of fit operating mechanisms should have. Figuring that the tightness is from elsewhere, I pushed the liner and piston out. The piston is really tight in the liner, especially when it nears TDC. It is so tight at TDC that I have to push the piston back down with a wooden dowel. I'm talking using a 5/16 dowel, supporting the liner on blocks and hitting the dowel with the ball of my hand. It is pretty much a light press fit at the bottom of the bore. I've rebuilt some automotive engines and I know in them, your looking at a couple thousands clearance between the piston and cylinder. I posted a picture of each side of the liner and piston. You'll see the one side of the piston has some galling, that can be slightly felt with the fingernail. With a bore light, I also found slight galling on the bottom side of the opening the exhaust port. The liner is a silver to straw color towards the bottom where the piston is a tight slip fit and at the top where it is very tight the liner is blue on the outside toward the back of the engine. The liner slips into the case with a nice slip fit and rotates freely, maybe about .001 clearance. Now here's the scary part, I have access to a Sunnen hone... I'm considering "dusting" the liner on the hone just until I get a slip fit. And yes, I have experience using a hone. It's not like I paid a fortune for this engine and it's some kind of jewel. It seems to me that I have to do something to get a free running fit between the piston and the liner. The engine is pretty much unusable as it is. Any ideas as to what caused this, or ideas for a better solution than honing the liner?