On October 3, 2006, about 1230 eastern daylight time, a Piper PA-24-250, N5097P, was substantially damaged when it impacted terrain while approaching Hammonton Municipal Airport (N81), Hammonton, New Jersey. The certificated private pilot was not injured. Visual meteorological conditions prevailed. No flight plan was filed for the flight, from Cross Keys Airport (17N), Cross Keys, New Jersey, to Hammonton. The personal flight was conducted under 14 Code of Federal Regulations Part 91. According to the pilot, the airplane was on a base leg to the airport when he turned on the auxiliary fuel pump, and the engine lost power. The pilot then performed a forced landing to a swampy area short of runway 21. A subsequent examination of the Lycoming O-540-A engine revealed that within the accessory section, the idler gear assembly, which normally transferred power from the crankshaft to the left magneto and the camshaft, had been displaced. The mounting shaft had also been displaced, the shaft hole was elongated, and the upper portions of both shaft mounting plate retaining screws were missing. The lower screw appeared to be sheared, while the remains of the upper screw exhibited mechanical damage. The crankcase surface around the upper screw hole exhibited fretting, and the idler gear had missing and damaged gear teeth. Remnants of the retaining screws and screw lockplate were found in the bottom of the crankcase. The failure sequence could not be determined. The pilot reported 1,393 hours of engine operation since overhaul. The engine logbook revealed that the engine was last overhauled on February 1, 1975. Lycoming Service Instruction 1009AS, "Recommended Time Between Overhaul Periods," recommended 2,000 hours of operation between overhaul. In addition, "All engines that do not accumulate the hourly period of time between overhauls specified in this publication are recommended to be overhauled in the twelfth year." However, there was no evidence that the calendar time since the previous overhaul contributed to the displacement of the idler gear assembly.