On February 19, 1994, about 1421 hours eastern standard time, a Cessna 172, N100DF, operated by the Maine Flight Center, Pittsfield, Maine, nosed over during landing roll at the termination of a forced landing near East Newport, Maine. The airplane was substantially damaged. The forced landing was precipitated by a loss of engine power during cruise flight. The certificated private pilot and his two passengers were not injured. Visual meteorological conditions prevailed and a flight plan was not filed. The personal flight originated from Bangor, Maine, about 1400 hours, and was conducted under 14 CFR 91. The pilot stated that he departed from Pittsfield, Maine, earlier in the day on a cross country flight. One quart of oil was placed into the engine prior to departure. Later during the flight, after about 3.5 hours of flight time, the pilot diverted to Bangor, Maine, because of low oil pressure and high oil temperature indications. After arriving in Bangor, the pilot requested oil for the airplane and a mechanic to inspect it. Four quarts of oil were placed into the engine and no maintenance was performed. The pilot examined the ground and the underside of the airplane and found no visible leaks. The mechanic told the pilot that "...low oil was normal on 172s." Deciding to continue the flight, the pilot started the engine, ran it up and determined that engine operation was "normal." He then departed Bangor en route to Pittsfield. About three minutes after reaching a cruising altitude of 4,500 feet mean sea level (msl), the engine temperature again rose rapidly with a concurrent drop in oil pressure. About one minute later, the engine seized. The pilot performed a forced landing into a soft, muddy field. The airplane nosed over onto its back during landing rollout. An examination of the airplane by an FAA aviation safety inspector revealed substantial damage to both wings and the fuselage. A hole about one inch in diameter was found in the engine crankcase near the no. 4 cylinder. The no. 4 connecting rod was fractured. The engine was disassembled and inspected by the FAA inspector on March 1, 1994, at the airport in Pittsfield. A report of the inspection is attached. According to the report: ...it was noted that this engine had experienced extensive wear to the piston pin plugs; (some were egg shaped), one was broken, the piston pin boss holes were badly worn, two lobes on the camshaft were severely pitted and the crankshaft bearings were worn considerably. The oil pump gears were virtually impossible to rotate by hand (gear striking the housing, which did not appear to be accident related) and the housing had considerable wear. Most noteworthy, during the investigation, was that an unauthorized piece of sheet metal had been installed on the front of the right rear engine baffle to block the flow of cooling air to the engine oil cooler.... No explanation ...can be given as to why the oil temperature did not "peg" flying many hours with the oil cooler air flow blocked, especially on a 45-degree day. A review of the engine maintenance logbook revealed that the engine had logged a total of 3153.3 hours without ever receiving a major or top overhaul. The FAA inspector stated, "...cause of this engine failure ...was due to high engine time ...resulting in excessive wear of internal parts."