Pull the top off and see if the ring(s) is stuck on the exhaust side of the piston. If so, pull the piston and do some ring and ring groove clean up. If the engine was not run real hot the ring will prolly still be good and regain the compression seal after all the carbon that wedged it into the ring groove is gone. Not all that often new rings are required. If you have 400-500 hours on the engine and the end gaps are wide, then you probably do, but generally no.