Incident Details
The pilot reported that while making the third pass on a cornfield, the engine tachometer dropped to 800 rpm. The pilot described the event as having "no popping, no warning, just low power." In response, the pilot executed a forced landing in the cornfield. Upon touchdown, the landing gear became embedded in the soft mud.
Aircraft Examination
A subsequent examination of the airplane's engine disclosed mechanical failures on the number four cylinder. The exhaust valve push rod was found broken, and the intake valve push rod was bent. No other anomalies were reported.
Conclusion
The investigation did not provide a probable cause for the push rod failures.