Accident Sequence
The pilot reported that while cruising at approximately 1,000 feet, the engine lost power. An autorotation was initiated. During the landing phase, specifically during the cyclic flare, the main rotor struck the tail rotor drive shaft.
Engine Examination
Examination of the engine revealed that the number two cylinder intake valve had failed in the top radius (neck area) of the valve keeper recess. This failure caused damage to the cylinder combustion chamber and piston.
Maintenance History
Inspection of the engine logbooks indicated that an identical failure had occurred eight hours prior to the accident. Further inspection revealed that the major engine overhaul, which had been conducted 27 hours before the accident, had not been performed in accordance with the manufacturer's procedures and specifications.