Engine Power Loss and Forced Landing
The pilot reported that the airplane was operating properly at 5,000 feet mean sea level until the propeller began to overspeed between 2,950 and 3,025 rpm, accompanied by an illuminated overspeed annunciator light. Attempts to slow the propeller with the propeller pitch control were ineffective. The oil pressure gauge read zero. The pilot reduced the throttle to about 15 inches of manifold pressure to slow the engine to 2,500 rpm.
Approximately 30 seconds to one minute later, the airplane started to shake and vibrate violently. White smoke filled the cabin, and oil covered the windshield. The pilot decided to execute a forced landing to a flat farm field. He lowered the landing gear and established a descent at about 90 knots. The engine was shut down by pulling the mixture to idle cutoff. The pilot slipped the airplane to lose altitude before landing.
During the landing roll, the airplane skidded in the mud for about 80 yards, and the landing gear retracted back into the wheel wells. The airplane sustained substantial damage.
Engine Examination
On-site inspection revealed a hole in the right side of the engine case. A teardown inspection found that the number 1 cylinder piston pin plug was fractured in two pieces. The smaller piece was deformed with substantial material loss, and its fracture surface was obliterated. The number 4 cylinder piston pin plug had rotated within the piston pin. Metal contamination was present in the oil pressure relief valve and valve seat.
A hole was found in the engine case next to the number 5 cylinder. The number 5 connecting rod was broken, with the rod end "hammered" and blackened. The number 5 rod bearing was scored and blackened. The number 1, 4, and 6 rod bearings exhibited melting and protruding. All main bearings were scored. The oil pump gears turned freely, but the pump walls were scored.
The number 1 and number 4 cylinder piston pins and piston pin plugs were examined at the National Transportation Safety Board's Materials Laboratory. The examination revealed that the number 1 cylinder piston pin plug had a fracture surface with visible crack arrest lines, features consistent with fatigue. Black deposits were observed on the head of the larger piece of the number 1 piston pin plug and on the ends of the number 4 cylinder piston pin plugs, though the deposits were less thick on the number 4 plug. An impression was observed on the larger piston pin plug piece in the bevel between the head and the shank, located on the same side as the fatigue origin, and covered with black deposits.
Recent Maintenance
The pilot reported that the engine had 1,000 hours of operation since its last overhaul and 47.7 hours since the last inspection. The engine was not equipped with an oil filter.