I was told that I had poor compression in cyl. #3 on a 4.3L OMC after replacing a head gasket. The boat overheated due to a worn rubber water propellor. I overreacted and pulled the motor. When I pulled the heads off everything looked OK. No scour marks on the walls, no gaps around the piston, everything looked OK. Could a bad adjustment on the valves been responsilble? The main question that I have is can I do a compression test with the engine out & sitting on the floor? I would think that it would be OK? Any thoughts will be greatly appreciated