On July 21, 1996, about 1430 Alaska daylight time, a wheel equipped Cessna 172XP airplane, N736LB, sustained substantial damage following a loss of engine power and subsequent forced landing on a rough gravel bar, located near the east end of Lake Clark Pass, about 60 miles west of Kenai, Alaska. The solo Private Pilot was not injured. The flight originated at King Salmon, Alaska, about 1230, and operated in visual meteorological conditions. A VFR Flight Plan was filed. During a telephone conversation with the NTSB investigator-in-charge (IIC) on 7/22, the pilot related the airplane was in cruise flight about 2,000 feet above the terrain when the engine began to run rough and make loud noises. He said the oil temperature gauge indicated a rise in temperature, and the oil pressure gauge showed a decrease in pressure. A small amount of oil splattered on the windshield, and the engine ceased to produce power. The pilot said he made several unsuccessful attempts to restart the engine. He selected a gravel bar a short distance behind the airplane as the most suitable landing area, and made a 180 degree turn to the gravel bar. Upon touchdown, the airplane rolled into an area of large rocks and undulating terrain, and the nose gear collapsed. The pilot reported damage to the firewall and the left wing. He also noted that the belly of the fuselage was coated with oil. The pilot said he was unaware of any preexisting mechanical problems with the airplane, and that the airplane had accrued approximately 8 flight hours since a recent annual inspection. He said he added one quart of oil prior to departure from King Salmon, which brought the oil level to the full mark (8 quarts). An inspection and disassembly of the engine was performed on August 13 at Wick Aero, Palmer, Alaska. Present were the NTSB IIC, and Anchorage FAA Inspectors Jim Ruckman and Gerald Martelli. The external inspection of the engine, a Teledyne Continental Motors IO-360-KB, serial number 2359C8-R, revealed an oval fracture approximately 3 inches long in the side of the engine casing directly over the number two piston rod. Removal of the engine's oil pan disclosed about a cup's worth of fragmented, pounded, and distorted metal debris. A portion of the metal fragments were identified as the remnants of the number two piston's connecting rod bearing cap, cap retaining bolts, and the number two connecting rod bearings. The engine was disassembled to the crankshaft. The number two piston connecting rod was fractured about mid span, with the fracture transecting approximately 3/4 of the rod. The piston rod was found separated from the crankshaft. Both the connecting rod cap bolts were examined and observed to have fractured about mid span. The fracture ends were elongated and necked down. The threaded, castellated nuts were still attached to the rod cap bolt ends. The number two piston rod crankshaft bearing journal was smeared and abraded. No other mechanical anomalies, other than those associated with the destruction of the number two piston connecting rod and bearings, were observed. The mechanic who helped recover the airplane from the accident site was in the shop at the time the engine was disassembled. He recalled that he drained in excess of 6 quarts of oil from the engine prior to the recovery. According to the owner and the aircraft's records, the engine had accrued approximately 240 hours since it was rebuilt to "zero" time tolerances by Teledyne Continental Motors in 1988.