On September 1, 1990, a Piper J3C-65 (registration N70659) was involved in an aviation accident near Opa-locka, FL. Investigators recorded the probable cause as: The separation of the connecting rod end cap was due to a lack of lubrication, which caused the rod bolts to stretch, lose their torque, and one nut to vibrate off; the other bolt failed due to overload. This summary draws on records from the U.S. National Transportation Safety Board (NTSB) historical archive.
During cruise, the engine seized after the number 3 cylinder connecting rod end cap separated due to a lack of lubrication. Oil covered the windshield, causing the pilot to overshoot the intended landing field; the aircraft struck a fence and nosed over.
Accident Sequence
During normal cruise flight, the pilot reported that the engine RPM was decreasing and the oil temperature was increasing. Shortly thereafter, the engine seized. The pilot attempted to land in a field, but poor forward visibility due to oil covering the windscreen caused him to overshoot the intended landing area. The aircraft subsequently collided with a fence and nosed over.
Examination Findings
Examination of the engine revealed that the number 3 cylinder connecting rod end cap had separated. The end cap exited the crankcase and came to rest in the oil sump. Lycoming engine personnel stated that the separation of the rod cap was due to a lack of lubrication. This lack of lubrication caused the rod bolts to stretch, losing their torque. One of the two nuts then vibrated off, and the other rod bolt failed due to overload.
The engine had received a top overhaul 136 hours prior to the incident and a major overhaul 2,122 hours earlier. Investigators were unable to determine the reason for the lack of lubrication.
Probable cause
The separation of the connecting rod end cap was due to a lack of lubrication, which caused the rod bolts to stretch, lose their torque, and one nut to vibrate off; the other bolt failed due to overload. The reason for the lack of lubrication could not be determined.