I have been given a smartech 23cc buggy to have a look at to see if I can get it running. The guy has changed the piston and ring in it and now the piston is running smoothly in the head but when I torque the head down the piston is hitting the top of the inside of the head. I checked that the piston is the correct size with the old one and it's exactly the same. So could it be the gasket that is too thin now as he used the old one.