On September 14, 2023, about 1300 central daylight time, a Cessna 182P airplane, N8443M, was substantially damaged when it was involved in an accident near Prospect, Tennessee. The private pilot and one passenger sustained minor injuries. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 personal flight. The pilot was performing a cross-country flight from Tuscaloosa National Airport (TCL), Tuscaloosa, Alabama, to Lebanon Municipal Airport (M54), Lebanon, Tennessee. About 1 hour into the flight, at 3,500 ft mean sea level, there was a “sudden severe engine vibration and loss of power.” He reduced the throttle to lessen the engine vibration. He elected to land the airplane in a soybean field since he was unsure if he would clear a large, forested area between him and the next closest airport. After touchdown in the soybean field, the nose landing gear struck a ditch, separated, and the airplane nosed over, coming to rest inverted. He called 911 and was met by first responders. Federal Aviation Administration inspectors responded to the accident site and examined the wreckage. The wreckage was found inverted, in the soybean field. There was no fire. The fuselage and empennage were substantially damaged. After recovery of the wreckage, the engine was examined on the airframe. The rocker covers were removed to examine the cylinder heads and check valve action. The Nos. 1-5 cylinders were normal in appearance and the valve action was correct. When the rocker cover for the No. 6 cylinder was removed, pieces of the exhaust valve rocker boss, the rocker, washers, and the rocker shaft were loose inside. The exhaust valve was closed. The rocker boss was fractured in two places. The loose parts recovered from the No. 6 cylinder were sent to the National Transportation Safety Board Materials Laboratory for examination. One of the rocker boss fragments exhibited features consistent with fatigue that initiated at multiple sites along the bore surface that had been in contact with the arm. The other boss fragment was fractured from overstress, exhibiting features consistent with rapid fracture of an aluminum casting. A review of the engine logbook revealed that the engine cylinders were removed, overhauled, and reinstalled on May 18, 2020, at 2,609.8 hours total aircraft time. At the time of the accident, the airplane had accrued about 154 hours since the cylinders were overhauled.