my 2nd motor was a new one. all i did was install it on my buggy to break it in. after 7 tanks of heat cycleing i started to run it in the drive way. then i heard a crunch and the motor stoped. i found that the back plate came right out. it must have been loose from the factory. needless to say i trashed the piston/sleeve and rod. now i pull them apart and clean and make sure all things are tight before i even turn it over.