Accident Summary
According to the pilot, the left engine began running rough at about 300 feet above ground level after takeoff. The roughness was accompanied by a slight left yaw. The pilot reported that the left engine was producing some power, so he elected not to feather the propeller. The aircraft would not maintain altitude; therefore, the pilot elected to make a gear-up landing in a wheat field.
Investigation Findings
An investigation revealed that the airplane had been involved in a previous gear-up landing and had accumulated 420 hours since then. An examination of the left engine showed that the propeller would rotate freely without rotation of the crankshaft. Further examination revealed that the spline bushing, part number 75462, turned freely in the front of the crankshaft, and the three dowels, part number 75359, were not in place. The bushing, which is pressed into the crankshaft during assembly, was loose enough to permit removal by hand. The dowels were found in the engine oil sump and were bent and deformed.