Bought a 1995 Wheel horse 246h cheap. Runs and cuts on full throttle but some smoke. Did std stuff to get down to one cyliner at 150-180 PSI, other cylinder at 0. Removed valve covers and the appear to function ok. Dont think a valve is stuck. Dead cylinder has piston at top of head but does slide if pushed with screw driver via plug hole. In process of removing engine. 1 - Have not replaced a piston or rings before. Once i have the bottom apart will i need to remove the heads to replace the connector rod, piston or rings? 2 - Do i need to do both cylinders or is the 150-180psi one ok? Hoping to make the horse run a long time.