Accident Overview
During cruise flight, the engine developed a massive oil leak and subsequently lost power. The pilot executed a forced landing at the nearest airport. Oil covering the windshield severely impaired the pilot's ability to see the runway, leading to a hard landing during which the landing gear collapsed.
Post-Accident Examination
Examination of the engine revealed the origin of the oil leak: a set-screw of improper length had been installed to retain the propeller governor idler-gear shaft. The screw was too short, which prevented proper staking to secure it in place against the shaft. As a result, the screw backed off, allowing the normally-stationary shaft to rotate. The rotating shaft then cut through an access plug on the front of the engine, enabling oil to drain overboard.
Maintenance History
Investigation determined that the set-screw was most likely installed during a sudden-stoppage inspection, at which time the idler gears were replaced. Lycoming Service Instruction 1343 describes the correct method for determining the required length of the set-screw and the proper installation procedure.
Conclusion
The accident was caused by an improperly short set-screw that led to a cascading failure: screw backing out, shaft rotation, plug breach, oil loss, engine power loss, and subsequent forced landing with obscured visibility and hard landing resulting in gear collapse.