On May 1, 1999, at 1130 central daylight time, a Narzinski Avid Flyer Mark IV, N313N, owned and piloted by a commercial pilot, sustained substantial damage during a forced landing, following a loss of engine power during cruise flight, near West Alton, Missouri. Visual meteorological conditions prevailed at the time of the accident. The personal flight was operating under the provisions of 14 CFR Part 91 and was not on a flight plan. The pilot reported no injuries. The local flight departed Creve Coeur Airport, Creve Coeur, Missouri at 1100. According to the pilot's written statement, after approximately 30-minutes of flight time, at an altitude of 1,400 feet above mean sea level, the engine experienced an uncommanded loss of power from 6,000 rpm to 5,400 rpm over a period of 4-seconds. The pilot reported that he established the airplane on best glide speed and prepared for an off-field landing while the engine experienced a constant depletion of power, finally loosing all power after a period of approximately 30 seconds. The pilot stated that he executed a forced landing into a farm field that had, "modest furrows". Substantial damage to the airplane was sustained during the landing. The Rotax 582 engine, serial number 4084252, was subjected to a tear-down inspection conducted by the NTSB Investigator-in-Charge and a representative of the engine manufacture. External visual inspection of the engine revealed a hole in the lower engine case on the Power Takeoff (PTO) cylinder side. Internal examination of the engine revealed metal deposits on the PTO cylinder dome, cylinder wall, and piston head. Examination of the PTO connecting rod revealed that the connecting-rod bearing had failed. Photos of the hole in the lower engine case, cylinder dome, cylinder wall, piston head, and connecting-rod are attached to this factual report.