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.