On June 20, 2014, about 1935 central daylight time, an experimental amateur-built Schumacher model Challenger II airplane, N441MS, was substantially damaged when it collided with power lines and terrain during a forced landing near St. Joseph, Illinois. The private pilot and passenger were not injured. The airplane was registered to and operated by the pilot under the provisions of 14 Code of Federal Regulations Part 91 without a flight plan. Day visual meteorological conditions prevailed for the local area flight that departed at 1900 from the pilot's private airstrip near Sidney, Illinois.The pilot reported that during cruise flight, about 1,200 feet mean sea level, the engine experienced a sudden and total loss of engine power. He was unsuccessful in reestablishing engine power and selected a nearby soybean field for a forced landing. The pilot stated that as he maneuvered the airplane toward the selected field, the setting sun temporarily obstructed his forward visibility and the airplane collided with power lines. He reported that following the collision with the power lines, the airplane entered an aerodynamic stall and impacted terrain with the left wing down. The airplane spun 180 degrees before coming to a stop in an upright attitude. The pilot and passenger unbuckled their seat restraints and exited the airplane uninjured. A postaccident examination of the airplane and its engine was performed by an aviation mechanic. The single fuel tank contained fuel and no anomalies were noted with its vented fuel cap. The engine produced suction/compression at each cylinder in conjunction with crankshaft rotation. Inspection of the spark plugs revealed features consistent with normal engine operation. Mechanical continuity was established between the cockpit engine controls and their respective engine components. An operational test run of the engine established the engine was capable of producing power. Following the operational test run, the intake and exhaust manifolds were removed to examine the pistons. The forward cylinder piston exhibited scoring and a lack of proper oil lubrication adjacent to the intake and exhaust ports. The rear cylinder piston did not exhibit scoring; however, evidence of oil starvation was observed. Further examination of the oil system revealed that the mechanical oil injection pump had seized within its housing. Additionally, the oil pump nylon drive-coupling had fractured. The oil pump was a non-serviceable component that prevented further disassembly. The pilot reported that the experimental engine, a Rotax model 503DIDC, was not originally equipped with a mechanical oil injection pump and that he had it modified with the oil pump about 50 hours before the accident.