Accident Summary
The airplane sustained substantial damage when it struck a tree and the ground during a forced landing. The forced landing was necessitated by a loss of engine power. Subsequent examination of the engine revealed a broken connecting rod and an oil level below the bottom of the dipstick.
Engine Examination
After the accident, the engine was inspected. The connecting rod was found to be broken. Additionally, the oil level measured below the bottom of the dipstick, indicating a low oil condition.
Propeller Governor Installation
According to the pilot and maintenance records, the airplane had recently completed an annual inspection. That inspection included an overhaul of the propeller governor. Examination of the governor installation showed that the mounting nuts did not have the proper stack-up of washers and were not torqued to specifications. The aircraft maintenance manual for this model specified the use of a single gasket between the governor and the engine accessory housing. However, an aircraft maintenance manual for later year models and an engine manufacturer's Service Instruction specified the use of two gaskets and a plate between the propeller governor and the engine accessory housing. The engine manufacturer's Service Instruction stated that the two gaskets and plate are necessary "to eliminate the possibility of oil leakage between the propeller governor and the accessory housing."