What happened
The pilot reported that following takeoff, the engine failed to develop adequate power for climbing or returning to the airport. Consequently, the pilot navigated down a canyon and executed a forced landing in a hay field. During the landing roll, the aircraft struck an unseen ditch, resulting in the collapse of the nose gear.
The investigation
A mechanical examination of the engine revealed that the number four exhaust valve was sticking. This mechanical failure prevented the engine from producing the necessary thrust for normal flight operations.
Findings
The airport elevation was recorded at 4012 feet. The primary factor contributing to the incident was the mechanical malfunction of the exhaust valve, which led directly to the loss of power and subsequent forced landing.