On April 16, 2012, about 1500 eastern daylight time, an experimental amateur-built Van's Aircraft RV-7A, N5025G, was substantially damaged during a forced landing to an agricultural field in Gerrardstown, West Virginia. The commercial pilot was not injured. Visual meteorological conditions prevailed. No flight plan had been filed for the local flight, which originated at Eastern West Virginia Regional Airport/Shepherd Field (MRB), Martinsburg, West Virginia. The personal flight was conducted under the provisions of 14 Code of Federal Regulations Part 91. According to the pilot, the airplane departed MRB about 1230, and during the flight, while maneuvering about 3,000 feet, the Mazda 13B rotary engine's coolant temperature rose. The pilot turned the airplane back toward the airport, and the engine seized and would not turn over during an attempted restart. The pilot advised MRB control tower personnel that he would have to land in a field, which included recently-planted apple trees. The pilot was able to land on a flat portion of the field; however, during the landing rollout, the airplane encountered a ditch that caught the nose wheel and bent the nose strut back, and the airplane nosed over. After the airplane was recovered from the field, the pilot, who was also the builder, disassembled the engine, which he stated had 4 hours of operation since it was rebuilt. The pilot first noted that the water pump, which was newly installed prior to the accident flight, had rust-colored water at the outlet hole from the pump bearing. The pilot also noted that a lot of metal had passed through the engine and the reduction drive, and that the stationary gear/bearing was frozen to the eccentric shaft. The pilot/builder further noted that during the recent rebuild, he had attempted to fine tune the engine by having the side and intermediate housings undergo lap grinding. The pilot/builder knew the grinding would require wider spacers, which he used, but those used may have been insufficient in width. The insufficient width resulted in bearing oil hole misalignment on the eccentric shaft which blocked oil from reaching rotating engine and reduction drive shaft parts.