I've just recently replaced a piston head that had a pretty decent gash in it, and also replaced the cylinder. Since I did this, the motor seems to have way too much compression. The piston and rings are 47mm, and I measured the cylinder to be 47mm also. I made sure no debris fell from the damage parts I replaced, and the engine is not siezed. The piston does move freely when turned manually from inside the clutch case, but this is while the cylinder head is off. With the head on, it will not move at all. Does anyone know if I've done something wrong, or what the problem might be?