Narrative
The pilot reported that during cruise flight at 3,500 feet, the engine lost power, behaving "just like it was running out of fuel." The pilot switched the fuel selector from the right main tank to the left, applied carburetor heat, and set the mixture to full rich. Two restart attempts were unsuccessful. The pilot selected a bean field for a forced landing, entering left traffic. On final approach, the pilot moved the fuel selector to the off position. The airplane touched down, rolled about 50 feet, and nosed over, coming to rest inverted. Recovery personnel turned the airplane upright, and an FAA inspector examined the scene.
Damage and Fuel Evidence
The upper fuselage and vertical stabilizer sustained structural damage. Two gallons of fuel were found in the left wing tank, with evidence of leakage at the accident site. The right main tank contained traces of fuel, also with leakage evidence. The airplane was transported to Salem, Indiana, for further FAA examination.
Engine Examination
A differential compression test confirmed earlier results from Tennessee. The No. 2, No. 3, and No. 6 rocker covers were removed, and the propeller was turned by hand. Crankshaft and connecting rod movement was observed, but no camshaft movement occurred during rotation. The accessory case was removed, revealing the crankshaft gear (part number 17725) in two pieces. The gear had failed at the two keyway slots. One key was partially separated, with a small portion found in the engine breather; the rest remained in the crankshaft. The other keyway was damaged. Parts were sent to the NTSB Materials Laboratory in Washington, D.C.
Metallurgical Findings
Examination of the crankshaft gear pieces showed that one fracture surface had features consistent with fatigue initiating in a corner of a keyway. A small radius had been cut into the larger radius of that keyway, creating a stress concentration point. The other keyway fracture displayed features consistent with an overload event.