Incident Overview
A private pilot was conducting a night cross-country flight when the engine began to lose power. Unable to maintain altitude to reach an airport, the pilot chose to land in a field. During the landing, the airplane impacted a barbed wire fence.
Post-Accident Inspection
An FAA airworthiness inspector, assisted by an aircraft mechanic, examined the engine. Upon removing the #2 cylinder's rocker arm cover, they observed that the exhaust valve adjuster locknut had loosened and had come completely off.
Maintenance History
Review of maintenance records showed that the #2 cylinder had been removed, repaired, and reinstalled on May 21, 2000, at an aircraft total time of 825.0 hours. The most recent 100-hour inspection of the airplane and engine occurred on August 13, 2001, at an aircraft and engine total time of 1,077.0 hours. The aircraft total time at the time of the accident is unknown.
Manufacturer Instructions
According to the engine operator's manual, persons installing pushrods for a cylinder are instructed to recheck the tappet clearance after run-in and to lock the valve clearance adjusting screw in place with the locknut.