Incident Overview
During cruise flight, an engine began vibrating violently and losing power without warning. The pilot-in-command was unable to maintain altitude and executed a forced landing in a soft, open field. During the rollout, the nose landing gear separated and the left main landing gear collapsed.
Engine Examination
Post-crash examination of the engine revealed that the 7/16-inch exhaust valve on the number 3 cylinder had failed.
Log Book and Maintenance History
The engine log books had been reconstructed after the original logs were lost. The reconstructed logs indicated that the engine had been overhauled in 1966, approximately 978 hours before the accident.
Airworthiness Directive Compliance
According to the reconstructed log books, an Airworthiness Directive (AD) requiring recurrent inspection and replacement of 7/16-inch valves and/or valve guides was considered not applicable due to the engine's serial number. However, the associated service bulletin listed the serial number as requiring compliance. No record of compliance with this AD note prior to the reconstruction of the log books was found. Additionally, no record existed to determine which camshaft was installed at the time of the reported overhaul.