On September 16, 1993, about 1200 central daylight time, a Cessna 172P airplane, N52502, experienced loss of engine power during cruise flight and landed off-airport near Fieldon, Illinois. The airplane was substantially damaged. The commercial pilot and passenger reported no injury. Visual meteorological conditions existed beneath an overcast. The personal flight originated from Bethalto, Illinois, about 1135 without a flight plan and operated under 14 CFR 91. The pilot states that while cruising at 2000 feet the sound of the engine changed. The pilot observed that the oil pressure gauge showed no pressure and the oil temperature gauge showed a normal temperature. After reducing the power, the pilot reported to ATC that he was experiencing an engine problem and was going to make a forced landing. The pilot states that the engine continually lost engine power and quit on final approach to an open field. The engine was disassembled at the manufacturer, Textron Lycoming, under the supervision of an FAA Inspector, on November 18, 1993. Inspection of the engine revealed a fractured connecting rod in the number three cylinder, a piston pin plug in the number one cylinder which had deteriorated into a small ball approximately one-tenth its normal size, extensive metal particulate matter contamination of the oil filter and throughout the engine, and distorted and discolored rod bearings.