On June 22, 1996, approximately 0730 mountain daylight time, a Grumman-Schweizer G-164A, N4698, was substantially damaged during a forced landing at Holyoke, Colorado. The commercial pilot was not injured. Visual meteorological conditions prevailed, and no flight plan was filed for the aerial application flight conducted under Title 14 CFR Part 137. The flight was originating when the accident occurred. The pilot said that shortly after takeoff, the engine began to vibrate and the control stick shook. He initiated a shallow left turn, and the engine began losing power. As he rolled out of the turn, the engine quit. He made a forced landing in a soft field and the airplane nosed over. The engine and propeller were examined at the facilities of Hershey Aircraft Services, Hershey, Nebraska. An FAA inspector from the Lincoln, Nebraska, Flight Standards District Office monitored the examination. Initially nothing was found that would explain the vibration and subsequent loss of engine power. Later, the oil sump was removed and ferrous metal was observed in the sump. The filters and screens, however, were clear of debris. A spokesman for Hershey Aircraft Services said there was evidence that the main bearing had failed, causing the engine to seize.