Incident Summary
Approximately 40 minutes into a flight, the pilot observed the tachometer surging. The oil pressure gauge subsequently dropped to zero, and the engine began emitting knocking sounds. The engine seized, forcing the pilot to execute a landing in a soybean field. During the landing rollout, the aircraft encountered large ruts, which caused the landing gear to collapse.
Engine Examination Findings
A post-incident examination of the engine revealed that the number six connecting rod had failed and punched a hole in the top of the crankcase. The number three upper piston pin plug had deteriorated, releasing aluminum particles into the engine. When the oil filter was opened, evidence of aluminum metal contamination was found. The camshaft and tappets exhibited various stages of spalling. Rust was observed inside all cylinder walls, and all connecting rods had surface rust. Additionally, the number four and five connecting rods were blued and did not move freely.
Maintenance History
The pilot reported that the oil filter was not opened during oil changes to inspect for metal contamination. Consequently, the pilot was unaware that the engine oil filter indicated the oil system was contaminated with metal particles.