What was found
OWNER REPORTED LOSS OF POWER, EXTREMELY ROUGH RUNNING ENGINE, UNABLE TO MAINTAIN ALTITUDE, FORCED LANDING. ENGINE INSPECTION FOUND NR 4 CYLINDER EXHAUST VALVE STUCK OPEN, BENT PUSH-ROD AND ROD HOUSING. BORESCOPE INSPECTION OF THE CAMSHAFT LOBE, LIFTER FACE, REVEALED NO OTHER FAILURE. INSTALLED NEW OEM CYLINDER, PISTON, RING ASSY, PN 05K21117, -35 PUSH ROD, AND NEW PUSH ROD HOUSING IAW MM. THE AIRCRAFT OWNER IS IN POSSESSION OF THIS CYLINDER IF NEEDED FOR FURTHER INSPECTION.