As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
DURING CRUISE FLIGHT, THE PILOT EXPERIENCED AN ENGINE VIBRATION.SUSPECTING A CYLINDER FAILURE, RETURNED TO BASE. TEMPS AND PRESSURES REMAINED NORMAL THROUGHOUT THE RETURN. MAINTENANCE INVESTIGATION REVEALED THAT THE NR 1 CYLINDER HEAD HAD SEPARATED FROM THE BARREL. THE CYLINDER ASSY WAS REPLACED AND THE AIRCRAFT WAS RETURNED TO SERVICE.