On July 3, 2003, at 1500 central daylight time, a Stinson 108-3, N6088M, registered to a private owner, operating as a 14 CFR Part 91 personal flight, lost engine power in cruise flight. The pilot made a forced landing in the vicinity of Hendersonville, Tennessee, and the airplane nosed over during landing roll. The airplane sustained substantial damage. Visual meteorological conditions prevailed and no flight plan was filed. The commercial pilot reported serious injuries, and the passenger reported minor injuries. The flight originated from Conway, Arkansas, on July 3, 2003, at 1215. The pilot stated he was in cruise flight at 3,500 feet, about 17 miles from the destination airport when he noticed a slight decrease in engine rpm and oil pressure. He started his descent to his destination airport and started looking for a forced landing area. The rpm continued to decrease, and he elected to make a forced landing to a grassy field. He made a base leg, turned final, and lowered the flaps to the full down position. On touchdown the landing gear collided with ruts that he did not see from the air, and the airplane nosed over. After exiting the airplane he observed the vertical fin was crushed and both wings had been damaged. Disassembly of the engine assembly showed three cylinders and three connecting rods had failed. The crankshaft journals of the failed connecting rods were heavily scored and burned. Portions of two connecting rod bolts were recovered from the oil sump. The bolts had severe necking and had plasticized. The oil sump was removed, and the oil pick-up screen was free of significant amounts of debris. The oil pump was removed and showed no signs of failure or contamination. The pressure regulator and pressure relief valve were examined and there was no evidence that either had failed. It could not be determined why the engine ceased oiling. Review of the airplane logbooks revealed the engine was overhauled on November 21, 2000, at tachometer time 2501.7. The tachometer was changed on May 15, 2003, at tachometer time 2678.4, and time since major overhaul was 176.7 hours. The tachometer at the accident site was 18.9 hours. The total time since major overhaul was 195.6 hours, and the total engine time is 2697.9 hours.