Take it apart and check it out. All just speculation right now. I bought a 345 off ebay and the piston and cylinder were toast. I bought a meteor piston that arrived before the saw. I noticed that the gouges were below the exhaust port, which meant it could still make compression. I figured since it was junk anyway, I may as well play with it and arbitrarily ported it. Just some "Ahh that looks good" no science about it. It was nasty when I took it apart, and it was still nasty when I put it together. I only cleaned what I needed to get it back together. The whole project was half of half-assed. I didn't even use a ring compressor, and you can't use your fingers on these ones. I cut a piece of scrap flashing and used that. Got it all together, and realized I needed to put the carb rubber on first, so I took it back apart, this has an rtv gasket. Then I put it back together again, never touched the rtv again. Got it all back together and maybe let it set up 5 or 10 minutes while I made the hole under the spark arrestor screen a little bigger, then started her up. She runs great and sounds like a little monster. Sometimes it's the stuff you do that you don't give a crap about that comes out the best.