Incident Overview
During cruise flight, the pilot observed that the engine became rough, oil pressure began to bleed off, and the tachometer fluctuated. These indications were followed by a complete loss of engine power. The pilot elected to perform a forced landing in a field.
Landing and Post-Impact
The airplane touched down and rolled approximately 240 feet before encountering soft dirt, which caused the airplane to nose over.
Engine Examination
Subsequent examination of the engine revealed that it would not rotate, though oil and fuel were present. The engine was disassembled for further inspection.
Crankshaft Fracture
The disassembly disclosed that the crankshaft had cracked completely through at the number one connecting rod journal. The fracture appeared clean with no exterior evidence of an existing crack or deterioration. However, the fracture surface contained ridges and valleys, and what appeared to be air bubbles near those ridges and valleys.