On February 24, 1998, approximately 1430 Pacific standard time, an experimental Cessna 150F, N8794G, nosed over during the landing roll following a forced landing after a loss of engine power near Fife, Washington. The private pilot and his passenger were not injured, but the aircraft, which was owned and operated by the pilot, sustained substantial damage. The 14 CFR Part 91 flight, which departed Auburn Municipal Airport, Auburn, Washington, about 30 minutes earlier, was being operated in visual meteorological conditions. No flight plan had been filed, and there was no report of an ELT activation. According to the pilot, the aircraft, which was registered in the Experimental Exhibition category, was powered by a modified Subaru Legacy automobile engine. He said that while demonstrating the aircraft to an acquaintance, the engine experienced a partial power loss. Soon thereafter, the engine lost all power, and the pilot elected to land in a nearby farm field. He said that his touchdown on the soft terrain was successful, but as he applied brakes to stop prior to an upcoming ditch, the nose wheel dug into the soft terrain and the aircraft nosed over. Although the owner, who was the individual that modified the engine for aviation use, was quite sure that a camshaft gear locating pin had failed, an engine teardown revealed that was not the case. Instead, it was found that the head on one of the two exhaust valves in the forward left cylinder had broken off of its stem and fallen into the cylinder. The piston itself had been torn into numerous small pieces and much of it was found laying in the cylinder. The piston pin was still in the end of the connecting rod, but none of the piston was still attached to the pin.