On July 31, 2016, about 1135 central daylight time, a Cessna 172F airplane, N211FC, collided with a berm during a forced landing near Newark, Illinois. The private pilot was not injured, and the airplane was substantially damaged. The airplane was registered to the pilot and operated as a Title 14 Code of Federal Regulations Part 91 personal flight without a flight plan. Day visual meteorological conditions prevailed for the cross-country flight that departed Wittman Regional Airport (OSH), Oshkosh, Wisconsin, about 0945, and had the intended destination of Morris Municipal Airport (C09), Morris, Illinois.The pilot reported that the airplane experienced a sudden loss of engine power about 1 hour 50 minutes into the flight at a cruise altitude of 2,500 ft mean sea level. The engine continued to run but there was an excessive vibration and a significant loss of power. The pilot reported that he increased the fuel mixture to full-rich, confirmed that the fuel selector was positioned to draw fuel from both fuel tanks, and verified that the ignition switch was selected to both. He did not engage the carburetor heat. There was no improvement to engine performance; however, the oil temperature and oil pressure gauges were indicating normal readings. The pilot reported that the engine eventually began to make a "squeaking" noise as it continued to run. The pilot stated that he made a forced landing to an open field because the engine was not producing enough power to maintain altitude. The airplane's nose landing gear collapsed when it impacted a berm during landing roll, and the airplane came to rest in a nose down attitude. The engine firewall and lower fuselage structure were damaged when the nose landing gear collapsed. The engine was examined by a Federal Aviation Administration (FAA) Inspector after the airplane had been recovered from the field. The FAA Inspector reported that although the engine crankshaft could be rotated by hand, it could not complete a full turn. The upper spark plugs were removed and examined. The upper spark plugs for cylinder Nos. 1-3 exhibited features consistent with normal operation. The upper and lower spark plugs for the No. 4 cylinder exhibited significant impact damage. The No. 4 cylinder was removed and revealed significant impact damage to the piston face and the top of the piston chamber. The No. 4 exhaust valve was not located in its normal position in the cylinder head. A portion of the exhaust valve was found embedded in the cylinder head. Another portion of the exhaust valve and the valve stem were found in the left muffler. About ½ of the No. 4 exhaust valve was located during the examination, and the recovered portions exhibited significant impact damage. The airplane was powered by a 145-horsepower, 6-cylinder, Continental O-300-D reciprocating engine, serial number 28231-D-3-D. The most recent annual inspection was completed on January 26, 2016. At the time of the accident, the engine had accumulated 2,146.9 hours since its last major overhaul that was completed on January 6, 1989. According to available maintenance documentation, the No. 4 cylinder exhaust valve had not been repaired or replaced since the last engine overhaul. According to the engine maintenance manual, the recommended time between overhaul (TBO) for the O-300-D engine is every 1,800 hours or 12 years, whichever occurs first. FAA regulations do not require Part 91 operators to comply with an engine manufacturer's recommended TBO interval provided the engine meets annual inspection requirements.