On October 2, 2007, at 1030 mountain standard time, a Cessna 172N, N6291D, sustained substantial damage during a precautionary landing subsequent to a partial loss of engine power near Green Valley, Arizona. The two occupants, the private pilot and passenger, were not injured. The aircraft was operated as a visual flight rules (VFR) personal flight under the provisions of Title 14, CFR Part 91. The airplane was owned by Tucson Aeroservice Center of Marina, Arizona. Visual meteorological conditions prevailed and no flight plan was filed. The local flight originated from Marana Regional Airport, Tucson, Arizona, approximately 30 minutes prior to the accident. In a written statement, the pilot reported that during cruise flight, the engine began to run rough and periodically backfire. The pilot attempted to troubleshoot the rough running engine without success and initiate a precautionary landing to a nearby road. The airplane struck two road signs and a barbwire fence during the landing rollout. Examination of the engine, by the Operator and a Federal Aviation Administration (FAA) Inspector, revealed that the number three cylinder exhaust rocker arm was disconnected from the cylinder due to the rocker arm hold down nut backing off. Review of aircraft maintenance records showed that 13.4 hours prior to the accident, the number one and three cylinders were removed to facilitate repairs to the cylinder hold down studs.