Accident Sequence
Approximately twenty minutes after departure, the pilot reported a loss of engine power while at an altitude of 8,500 feet. The airplane was over hilly terrain at the time. The pilot circled the area and attempted to restore full engine power, but those efforts were unsuccessful. Subsequently, the pilot selected a forced landing site and initiated an approach.
During the final approach to the chosen landing area, the airplane collided with trees. After striking the trees, the aircraft impacted rapidly rising terrain and caught fire.
Engine Examination
Post-accident examination of the engine revealed that the number four intake valve was fractured and remained stuck in the open position. Closer inspection of the fracture surface showed multiple fatigue origins. Additionally, the valve guide for the number four cylinder was found to be oversized by 0.030 inches.