On September 9, 2000, at approximately 2230 mountain daylight time, a Cessna R172K, N1036V, was substantially damaged when it collided with terrain during a forced landing. The private pilot and two of his three passengers were not injured. The third passenger received minor injuries. Night visual meteorological conditions prevailed for this personal flight operating under Title 14 CFR Part 91 and no flight plan was filed. The flight originated at Centennial Airport, Englewood, Colorado, at 2200 hours. The intended destination was Front Range Airport, Watkins, Colorado. The pilot stated that, while in cruise flight at 1,800 feet above ground level, the engine started to run rough and began to vibrate. He noticed that the propeller rpm was increasing and when he cycled the propeller control lever, no change in propeller rpm was noted. He observed that both the tachometer and engine oil pressure gauges were indicating zero. The engine started to make "popping and clunking" sounds and the vibrations increased until the engine seized. The pilot made an emergency decent and completed a forced landing in a rough field. Upon impact with the ground, the nose gear strut collapsed buckling the firewall. The airplane also sustained damage to the belly and propeller spinner. A post accident engine teardown examination of the Continental IO-360K engine revealed that the engine oil pump shaft or "idler pin" for the driven gear had worked free from its pressed-in position on the accessory case. The pin had fractured through the engine oil pump cover plate and came in contact with the tachometer drive gear fracturing the tachometer drive gear shaft. Further examination of the engine provided evidence that a type of sealant had been used to stop an oil leak at the lower mounting surface of the tachometer drive assembly and around the idler pin for the oil pump driven gear. The sealant was applied to the outside of the accessory case below the tachometer drive cover plate and under the alternator gasket adjacent to the idler pin. The machined hole for the idler pin is in the accessory case directly under the mounting surface of the alternator at the twelve o'clock position. A product analysis manager from Teledyne Continental Motors in Mobile, Alabama, provided the following statement: "The idler pin worked loose in the accessory case during service. The looseness caused oil from the oil pump to be pumped through the pivot and accessory case, leaking externally. Sealant was on the external gasket in an attempt to prevent leakage. The sealant pushed the loose pivot hard into the oil pump cover plate bore, bottoming out. As pressure was applied from the sealant, hydraulically, the cover plate broke out at the pivot hole. The pivot eventually moved outward and hit the drive gear, shaving away the teeth. The pump, as the condition worsened, locked up the drive gear shearing the pump drive, resulting in loss of oil pressure."