Event
During the initial climb after takeoff, the aircraft experienced a partial loss of power. The engine's revolutions per minute (rpm) decreased to 1,500, accompanied by roughness. The certified flight instructor (CFI) took control from the student pilot, executed a 180-degree turn back toward the runway, and landed hard on a taxiway.
Both pilots reported no discrepancies during preflight, engine start, taxi, or run-up.
Engine Examination
Post-incident examination of the engine revealed that the number 3 exhaust valve was broken, and the valve head was found embedded in the piston.
Maintenance History
Review of the engine logbook showed that the engine had accumulated 3,711.0 hours since its last major overhaul, which occurred on November 30, 1993. According to the engine manufacturer, the maximum recommended time between overhauls is 2,400 hours or 12 calendar years.
A Lycoming Mandatory Service Bulletin addresses the need to inspect exhaust valves and valve guides to prevent sticking and possible failure due to excessive guide wear. The bulletin recommends inspections at 400-hour intervals. No record of compliance with this bulletin was found in the logbooks.