On August 18, 1995, at 1535 Pacific daylight time, N9531Y, a Beech P-35, operated by the owner/pilot, ditched in Lava Lake near Bend, Oregon, and was substantially damaged. The ditching was precipitated by a total loss of engine power during cruise flight. The commercial pilot, the sole occupant, was not injured. Visual meteorological conditions prevailed and no flight plan had been filed. The business flight departed from North Bend, Oregon, and was destined for Alfalfa, Oregon. The flight was conducted under 14 CFR 91. The pilot stated that he was in cruise flight at 7,500 feet above mean sea level for about 45 minutes when he noticed a loss of oil pressure and an increase in oil temperature. Shortly thereafter, he noticed oil on the engine cowling and a "funny" noise. The engine immediately lost all power and the pilot initiated a forced landing. The pilot stated that there was no suitable terrain for a safe landing beneath him, so he elected to ditch the airplane in a lake. According to an FAA aviation safety inspector from Reno, Nevada, who was also a witness to the accident, the airplane circled the lake during the emergency descent. The flaps were fully extended and the landing gear was retracted as the airplane approached the lake. The airplane was observed to land tail first and come to a stop in the water with its nose down. The pilot exited the airplane. About two minutes later, the airplane sank in about 30 feet of water. After the airplane was recovered, the FAA inspector performed a cursory external examination. He reported that the engine had a hole in the crankcase above the number 4 cylinder. He also reported that the airplane was substantially damaged due to the impact with the water. Structure in the vicinity of the leading edge of the left wing root was deformed. The engine, a Continental IO-470-LCN, was removed from the airframe for investigative purposes. The engine was subsequently disassembled and inspected by the Safety Board on January 18, 1996, in Mobile, Alabama. The no. 4 connecting rod was found separated from the crankshaft at the end cap. The rod end cap bolts had separated from the cap and exhibited evidence of necking and heat distress. The crankshaft was intact. The no. 4 rod journal exhibited evidence of heat distress; the no. 3 rod journal did not. These two journals share the same oil gallery. All other crankshaft oil passages were also verified open and unrestricted. The bearings associated with the no. 4 rod journal were destroyed. All other rod journals and all of the main bearing journals did not exhibit evidence of heat distress or lack of lubrication. About 1.5 quarts of oil were found in the oil sump, along with shavings of bearing material. The oil screen and oil pump did not exhibit evidence of malfunction or blockage. All six piston faces did not exhibit evidence of preigintion or detonation. An examination of excerpts from the engine log books revealed that the engine had undergone an 100-hour inspection 16 months prior to the accident. The engine accumulated 20 operating hours since the inspection. Entries in the log books also indicated a total engine time of 2,328 operating hours, and 925 hours since its last major overhaul. No unresolved discrepancies were noted in the most recent entries in the log books. The pilot reported that he had never noticed any engine abnormalities prior to the accident.