Engine Failure
During normal cruise flight, the number one cylinder exhaust valve head separated from the valve stem. This event resulted in a significant loss of engine power.
Forced Landing and Ground Loop
The pilot initiated a landing approach to a farm field. On final approach, the pilot observed that the field contained rough and rising terrain. While performing a slight right turn at an altitude of approximately 10 feet above the ground, the aircraft's wing contacted some weeds. Subsequently, the aircraft ground looped.
Investigation
The reason for the exhaust valve head separation could not be determined during the investigation.