On August 10, 2002, about 1108 central daylight time, a Bellanca 17-31A, N39835, operated by a private individual as a Title 14 CFR Part 91 personal flight, struck a fence during a forced landing near Gainesboro, Tennessee. Visual meteorological conditions prevailed. No flight plan was filed. The airplane was substantially damaged. The private-rated pilot and one passenger received minor injuries. The flight had originated from the Jackson County Airport, near Gainesboro, Tennessee, about 1040, en route to Somerset, Kentucky. The pilot stated that he was cruising at about 3,500 feet when the airplane's engine began vibrating. He said he looked at the engine instruments but found no abnormal indications. He further stated that he attempted to return to the Jackson County Airport, but was unable to maintain altitude and at about 1,800 feet the engine stopped operating. He said he approached an open field, and was about to land when the landing gear impacted a barbwire fence and collapsed. The right wing then hit a post and the airplane veered to the right before coming to rest. The accident site was about ten miles west north west of the airport. According to the FAA inspector's statement, examination of the wreckage revealed that the airplane was lying on its belly with the landing gear torn loose. The fuel caps were removed, the fuel tanks all showed "fuel was available," and the fuel appeared blue. The fuel selector was checked and it indicated that fuel was being drawn from the left wing. The primary fuel valve was found "on main." The engine cowling was removed and number 3 cylinder was pushed away from the case. The cylinder studs were stripped as though the nuts had been "force off without rotating." Oil had blown through the cowling area. The oil filter and oil filler cap was in place and no other catastrophic damage noted. The propeller was slightly bent aft on two blades. Atlanta Air Salvage. Inc., Griffin, Georgia, conducted an engine teardown, which revealed that a main bearing on the crankshaft journal had spun; causing a reduction in forced oil lubrication, and seized the connecting rod, which forced the cylinder away for the case. The cause of the spun main bearing, which forced the cylinder displacement, was not determined.