As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
PILOT NOTED A SUDDEN ROUGHNESS IN THE ENGINE FOLLOWED BY A 200-300 RPM LOSS. MADE A SAFE EMERGENCY LANDING. DISPATCHED A MECHANIC TO DETERMINE CAUSE. THE INTAKE PUSHROD AND TUBE WERE SEVERELY BENT. THE LOWER SPARK PLUG WAS BADLY LEAD FOULED. SUSPECT CAUSE WAS DETERMINED TO BE EITHER DETONATION OR THE INTAKE VALVE STICKING MOMENTARILY. THE ENGINE WAS REMOVED FOR OVERHAUL.