On February 24, 2002, at 1311 mountain standard time, a Piper PA-32R-300, N47465, was substantially damaged when it struck a truck parked on a highway shoulder during a forced landing near Ferron, Utah. The pilot and three passengers received minor injuries. Visual meteorological conditions prevailed, and a VFR flight plan had been filed (but not activated) for the personal flight being conducted under Title 14 CFR (Code of Federal Regulations) Part 91. The flight originated at Duchesne, Utah, approximately 1245, and was en route to Cedar City, Utah. According to the pilot's accident report, he departed Riverside, California, on February 23, and flew to Duchesne to attend a wedding. The next afternoon, he departed Duchesne and was en route to Cedar City, Utah. Approximately 30 minutes into the flight, the engine began to "miss." Ten minutes later the engine began to "backfire heavily and sputter." The number 1 cylinder temperature "shot off the gauge" with a red warning light illuminated. The engine lost power and the airplane began to descend. The pilot transmitted a "Mayday" that was heard by a passing United Air Lines flight, and relayed to authorities. He started looking for an area to land and saw a road 5 miles to the east. The pilot wrote, "I had strong x [cross] -winds blowing me off my line of approach". He landed on Utah State Route 10, at milepost 3.5, near Ferron, and attempted to stay in the right lane to avoid a pickup truck that was parked on the shoulder of the highway. During the landing roll, the airplane struck the truck, shearing off its left wing. The airplane then overturned and skidded 300 feet to a halt. On April 4, 2002, the engine was examined by a Textron-Lycoming investigator at the facilities of Air Transport in Phoenix, Arizona. After removing the single drive dual magneto from its mounting pad, extensive damage to the accessory gears was noted. Removal of the accessory case disclosed the magneto idler gear (photo 5) was missing eight (8) teeth, 3 of which were displaced from the gear and exhibited signatures consistent with mechanical overload, and the remaining five (5) had been ground off (photo 6). The magneto idler gear drives the dual magnetos. The idler gear shaft bore at the back of the crankcase (photo 7) and the accessory housing (photo 8) were missing approximately 1/3 of their circumferential material, and the inside surfaces were polished, burnished and elongated (photo 11). The fracture surface(s) exhibited signatures consistent with overload. The overload forces appeared to have been applied inboard, evidenced by the symmetrical displacement of the bore material at each end of the subject idler gear shaft. The oil sump contained the three gear teeth and a piece of aluminum debris with gear tooth impressions matching the size and shape of the missing teeth (photo 9). The oil suction screen contained similar material (photo 10). It appeared the idler gear had been misaligned for some time of the mating surfaces. The oil filter contained slivers and particles of non-ferrous material similar to aluminum (photo 12). The airplane maintenance records were reviewed. At the time of the accident, the engine had accumulated 3,856.2 hours total time-in-service, and 1,256.6 hours since its last major overhaul. The tachometer read 2152.7 hours and the Hobbs meter read 2317.4 hours. The overhaul entry did not indicate the scope and detail of the work performed, the date it occurred, nor who performed the work. Between March 31, 1997, and October 15, 2001, there were seven maintenance entries indicating the oil and oil filter had been changed, but neither entry indicated whether the filter had been inspected as outlined in Lycoming Mandatory Service Bulletin SB-480D.