It's the easiest thing in the world to figure out if it's bearings or the pinch. Just take the p/s out and turn it over. Is it smooth? p/s back in. Is it sticking now? Now you know. I've had motorcycle pistons get hot and gall up on the cylinder and have kind of the piston tightening effect he's describing but I've never seen it on one of these little motors. I don't know if it would do that or not.
While running a break in, did you ever notice the engine suddenly runs a bit heavy and slowly comes back to normal again? That was such a moment the piston did grow and polished off again. For several years I was involved with an engine development and have broken in many engines and have seen this grow many times. I was told some manufacturers put their pistons or piston material in an oven to give them a 1st heat treatment to lower this effect.
Originally Posted by
1995 Monster T
More oil lube will fix the problem.
So a grown piston can be fixed with some oil? Oh wow!