Hi all I have a strange problem with my plus 35. It's had around 20-25 litres run through it have changed rods an bearings regularly. But last club day went to start if and it kept locking up like a new motor. So I pulled it down everything looks fine no marks the rods perfect but the piston will only slide half way up the sleeve. An jams like it needs to be run in again. What could cause this can the piston expand and not shrink back?