On April 19, 1997, about 1320 eastern daylight time, a Stinson 108-1, N9063K, registered to a private owner, operating as a Title 14 CFR Part 91, local personal flight, nosed over during a forced landing, near Smithfield, North Carolina. Visual meteorological conditions prevailed and no flight plan was filed. The airplane was substantially damaged. The commercial pilot was not injured. While in cruise flight the pilot noticed that the engine "became a little rough," oil pressure was bleeding off and the tachometer was fluctuating, followed by a complete loss of engine power. The pilot elected to land in a field, touched down, rolled about 240 feet, before the "soft dirt" caused the airplane to nose over. Examination of the engine revealed it would not rotate, oil and fuel were present. The engine was disassembled on May 5, 1997, under the supervision of the FAA, and according the FAA Inspector's statement; "...it was noted that the crankshaft had cracked completely through at the number one connecting rod journal. This crack appeared to be clean with no exterior evidence of an existing crack or deterioration of any kind. The crack did have within it ridges and valleys and what appeared to be air bubbles near those ridges and valleys...."