On August 22, 2003, at 0630 mountain standard time, an Ercoupe 415-C, N3182H, collided with a drainage ditch during a forced landing following a loss of engine power near Saint Johns, Arizona. The student pilot/owner was operating the airplane under the provisions of 14 CFR Part 91. The pilot was not injured, and the airplane sustained substantial damaged. Visual meteorological conditions prevailed, and no flight plan had been filed. The local flight originated at Saint Johns Industrial Airpark about 0545. The pilot reported to the National Transportation Safety Board investigator-in-charge (IIC) that he had been flying south east of Saint Johns Industrial Airpark, and was approaching runway 32 for landing. Just before he turned onto an extended final approach the "engine started hammering." The pilot was not able to increase the engine power enough to maintain level flight. He executed a forced landing on a dirt road one and half miles east of the airport. Upon landing, the airplane veered off a curve in the road into a drainage ditch, which collapsed the nose gear. The airplane then nosed over on the other side of the ditch. Engine data The Teledyne Continental C-75-12 engine received its last annual inspection on November 7, 2002. The number 1 cylinder assembly had been replaced on January 18, 2003. The engine logbook records that on January 18, 2003, the time since overhaul was 899.39 hours, and the total engine time was 2,538.38 hours. The date of the last engine overhaul was July 20, 1967. The airplane had a Federal Aviation Administration Supplemental Type Certificate (SE634GL) approving the use of unleaded automotive gasoline. A Teledyne Continental Service Information Letter, SIL98-9A, specifies the recommended time between engine overhauls. For the C75 engine, it listed the time between overhaul (TBO) as 1,800 hours or 12 years, which ever occurred first. Engine Examination A Federal Aviation Administration inspector examined the airplane's engine and reported that the exhaust valve on the number two cylinder had separated at the stem. The spark plug on the number four cylinder was loose.