Accident Overview
During the first flight following the installation of an overhauled engine, propeller, and propeller governor, the aircraft's engine lost power. The pilot executed a forced landing on an interstate highway situated in a major metropolitan area. The pilot reported selecting the highway as a landing area because "everything else was rooftops." During the landing, the left wing of the airplane struck a car.
Engine Examination
Post-accident examination of the engine revealed an uncontained catastrophic failure of the number four connecting rod. Significant heat distress was observed at the number four connecting rod and adjacent components, consistent with a lack of oil lubrication. The oil dipstick did not register any oil in the sump, and a substantial oil film was present on the firewall and belly of the aircraft.
Propeller Governor Installation
Investigation of the propeller governor disclosed that it had been installed contrary to the engine manufacturer's Parts Catalog and Service Instructions. Specifically, a single gasket was used to mount the governor instead of the required plate sandwiched between two gaskets. A clear and evident oil path was visible from the edge of the single gasket. The improper installation allowed engine oil to leak overboard, which resulted in a loss of lubrication and subsequent failure of the number four connecting rod.