Incident
During the initial climb after takeoff, when the airplane reached approximately 300 feet above ground level, the engine began to run rough. The private pilot initially attempted to turn back toward the airport, but the flight instructor assumed control of the airplane. The instructor executed a forced landing, during which the airplane struck trees.
Examination
An FAA inspector conducted a subsequent examination of the engine. The inspection revealed valve guide wear and coking on the valve stem of the number four cylinder exhaust valve. When the inspector repositioned the valve, it stuck in both the open and closed positions.
Maintenance History
A review of the airplane's logbooks indicated that the engine had accumulated 1,975.49 hours of operation since its original manufacture, approximately 33 years prior to the accident. During that entire period, the engine had never been overhauled. The engine had accumulated 23 hours of operation since the last annual inspection, which was performed approximately 10 months before the accident. The engine manufacturer had issued a service bulletin and service instruction recommending that valve guides be inspected at 400-hour intervals and that the engine be overhauled in the 12th year if it did not accumulate the recommended hourly period between overhauls, which was 2,000 hours.