Background
Shortly after takeoff, the aircraft leveled at 1,500 feet MSL, and the pilot set engine power to 2,450 RPM. Soon thereafter, a partial power loss occurred.
Accident Sequence
The pilot attempted unsuccessfully to regain power, then turned back toward the departure airport. On the initial approach, the pilot was too high and executed a go-around. While circling to land, additional power loss occurred, and the pilot was unable to continue the flight. A forced landing was made on a highway. During the approach, the aircraft struck a guy wire.
Examination Findings
Examination of the engine revealed that the number three cylinder exhaust valve head had separated. Fragments of the valve head were found inside the number two cylinder. Metallurgical examination of the valve head indicated that it had been exposed to above-normal temperature, and the fracture was consistent with overstress.