Summary
During a cross-country flight, the airplane experienced a complete engine seizure. The pilot executed an emergency landing, during which the front wheel became caught in sandy soil, resulting in the airplane nosing over. Subsequent examination of the engine identified significant mechanical failures.
Engine Examination Findings
An examination of the engine revealed that one connecting rod bolt nut from the No. 4 connecting rod was missing from the bolt and was found loose within the crankcase. The No. 4 piston pin boss was broken, and the piston pin was also found loose in the crankcase. The No. 4 connecting rod bearings were destroyed. Additionally, the connecting rod bolts on the No. 1 and No. 2 connecting rods were not at the prescribed torque.
Conclusion
The source document provides no explicit statement of probable cause.