What happened
While flying above hilly terrain southeast of the airport, the pilot of the aircraft heard a loud bang followed by violent vibrations originating from the engine. Although the engine did not suffer a total loss of power, performance was severely degraded by the vibration. The pilot observed that reducing the throttle caused the vibration to subside, but increasing power caused the violent shaking to return.
Determining it was unsafe to continue the flight, the pilot searched for an appropriate landing site and executed a forced landing in a pasture. The landing was initially uneventful; however, one of the main landing gear struck a deviation in the ground. This impact caused the aircraft to nose over and come to rest in an inverted position. There were no injuries reported.
The investigation
A mechanic who recovered the wreckage examined the engine and identified that the number 3 cylinder exhaust valve was stuck. The inspection also revealed that the corresponding push rod tube was bent, though the number 3 connecting rod remained intact.