As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
NR 3 CYLINDER EXHAUST VALVE SEPARATED THE STEM FROM THE HEAD. AIRCRAFT WAS FORCED TO LAND. ENGINE HAD GOOD HISTORY OF MAINTENANCE. THE ENGINE WAS NEW IN 1977. SUBMITTER SUGGESTS THE INDUSTRY SHOULD BE REQUIRED TO REMOVE THE EXHAUST SYSTEM AND INSPECT VALVES FOR CORROSION IN A CALENDER TIME FRAME.