On July 21, 2003, approximately 1245 mountain daylight time, a Cessna 182S, N146NE, impacted the terrain during an attempted forced landing in a field near Henry's Lake, Idaho. The private pilot and his four passengers were not injured, but the aircraft, which is owned and operated by the pilot, sustained substantial damage. The 14 CFR Part 91 personal pleasure flight, which was en route to Pocatello, Idaho, departed Henry's Lake Airport about 10 minutes prior to the accident. No flight plan had been filed. The aircraft was being operated in visual meteorological conditions. According to the pilot, about five minutes after takeoff, the oil low pressure light illuminated and shortly thereafter he heard a knocking sound coming from the engine. He therefore shut the engine down and attempted to return to the airport of departure. Although he attempted to stretch his glide so that he could return to Henry's Lake Airport, he was unable to do so, and eventually had to make a power-off landing in a field about one mile from the runway. Although the touchdown was uneventful, during the landing roll, the aircraft encountered a ditch, which resulted in the separation of the nose gear and substantial damage to the aircraft structure. On July 22, 2003, a Federal Aviation Administration (FAA) Inspector from the Salt Lake City, Utah, Flight Standards District Office arrived at the accident site and inspected the aircraft. The inspector reported that oil residue was noted at the aft end of the engine around the accessory section. After the tail was lowered, a noticeable oil leak was noted around the vacuum pump flange (approximately 6 drops per minute). On August 7, 2003, another inspector from the FAA inspected the engine. The inspector reported that, "It was obvious the pneumatic pump gasket had failed..." and "...was blown out the top between the mating surfaces of the pump and the mounting pad." The inspector further reported that the four mounting nuts of the pump were only "slightly more than finger tight." All four nuts were removed with no resistance. The internal star locking washers were in place under the nuts and had been crushed. Standard torque on these nuts is 90" pounds. A review of maintenance records indicated that on October 23, 2002, at a tach time of 763.8 hours, Mandatory Lycoming Service Bulletin No. 554 was accomplished to replace the crankshaft gear retaining bolt. During this process, the removal of all accessories on the accessory housing was required. At the completion of the work, an engine test run was accomplished, as well as a leak check. No other maintenance had been accomplished on the engine except for an oil change on June 5, 2003. Approximately 116 hours had been accumulated on the engine at the time of the accident since the Service Bulletin accomplishment. The aircraft is equipped with four seats. The pilot reported that a three-year-old child was sharing a seat and seatbelt with the passenger in the left rear seat.