On June 30, 2000, about 0800 central daylight time, a Piper PA-36-285, N11A, piloted by a commercial pilot, sustained substantial damage during a forced landing following a loss of engine power near Saint Vincent, Minnesota. The 14 CFR Part 137 aerial application flight was not on a flight plan. The pilot, who was the sole occupant was not injured. Visual meteorological conditions prevailed at the time of the accident. The flight originated from the Pembina Municipal airport (PMB), Pembina, North Dakota, at 0700, and was returning to PMB when the accident happened. In a written statement the pilot said that he had finished spraying a field and, "...was returning to [the] airport of departure (Pembina). After pulling out of field I felt an abnormal vibration, I pulled the throttle back 100 rpm and it seemed OK. After only approximately 1/2 mile the engine shook violently and quit." The pilot said that he was only about 150 feet above ground level when the engine failure occurred. The airplane was subsequently landed in a wheat field where it was damaged. A Continental 6-285 "Tiara" geared engine powered the aircraft. A postaccident examination of the aircraft by a Federal Aviation Administration Inspector revealed that the prop driver gear shaft on the engine was protruding out of the front of the engine approximately one inch further than normal. The engine could not be rotated by hand. No disassembly of the engine was performed. No other engine or airframe anomalies were detected that could be associated with a preexisting condition.