As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
DURING FLIGHT ENGINE STARTED RUNNING ROUGH AND WOULD ONLY DEVELOP 1800 RPM. PILOT LANDED WITHOUT INCIDENT. UPON INSPECTION FOUND NR 3 CYLINER ROCKER SHAFT BOSS BROKEN AND SHAFT AND ROCKERS LAYING LOOSE IN THE ROCKER BOX COVER. THE PUSH RODS WERE STRAIGHT AND THE VALVES WERE NOT STUCK. (M)