On August 26, 1995, at 1912 eastern daylight time, a Cessna R172K, N1439V, lost engine power and made a forced landing in an open field at Lisbon, Ohio. The certificated commercial pilot, the sole occupant, was not injured. The airplane sustained substantial damage. Visual meteorological conditions prevailed for the flight, no flight plan was filed. The local flight originated from East Liverpool, Ohio, and was conducted under 14 CFR 91. The pilot reported that he was operating the airplane over the fairgrounds, towing a banner, when he noted a complete loss of oil pressure. He stated that when he tried to return to the airport, the engine lost power and he made a forced landing in a freshly mown hay field. The pilot reported that the airplane was damaged when it went over a drop off during the forced landing/landing roll. The airplane was examined after the accident by the Federal Aviation Administration (FAA) Inspector. The examination revealed that the oil filter adapter separated from the boss of the crankcase cover. According to the FAA, about 80% of the threads in the crankcase cover boss were stripped.