Incident Summary
A pilot experienced engine roughness while flying south of Overton, Nebraska, prompting a forced landing. The pilot selected a corn stubble field for the landing. According to the pilot, the touchdown was normal, but during the landing roll, the aircraft contacted a snow drift and nosed over, coming to rest inverted.
Engine Examination
Post-accident examination of the engine revealed that the number 4 cylinder exhaust valve guide was sticking, and the exhaust valve was not seating properly. This condition likely caused the engine roughness reported by the pilot.
Sequence of Events
The pilot reported that the engine began running rough, leading to the decision to land immediately. After a normal touchdown on the corn stubble field, the rollout was uneventful until the aircraft struck a snow drift. The contact with the snow drift caused the aircraft to flip onto its back.