What was found
DURING CRUISE FLIGHT, PILOT REPORTED ROUGH RUNNING ENGINE. PILOT REDUCED POWER AND LANDED SAFELY WITHOUT INCIDENT. MECHANICS INSPECTING THE ENGINE DISCOVERED A SEVERELY BENT PUSH ROD AND HOUSING ON NR 1 CYLINDER. FURTHER INSPECTION REVEALED THE EXHAUST VALVE STEM CAP SEPARATED FROM THE VALVE STEM AND LODGED BETWEEN THE VALVE ROCKER AND VALVE STEM. MECHANICS DETERMINED THIS MALFUNCTION WAS APPARENTLY CAUSED BY THE EXHAUST VALVE STICKING FROM EXCESSVIE CARBON BUILD-UP.