On June 30, 2002, at 1230 central daylight time, an amateur-built Waltz RV-8, N877TC, owned and piloted by an airline transport pilot, sustained substantial damage during a forced landing to a soybean field near Omaha, Nebraska. Visual meteorological conditions prevailed at the time of the accident. The personal flight was operating under the provisions of 14 CFR Part 91 without a flight plan. The pilot and his passenger reported no injuries. The flight originated at Creve Couer Airport, St. Louis, Missouri, at 0950 and had the intended destination of Millard Airport (MLE), Omaha, Nebraska. The pilot reported the airplane experienced a propeller overspeed condition during a descent, with the propeller speed increasing to 3,170 revolutions per minute (rpm). The oil pressure subsequently began to fluctuate between 17 and 26 pounds per square inch (psi). The pilot noted he monitored engine indications for approximately two minutes and did not observe any changes in engine condition. The pilot stated that "loud banging noises began emanating from the engine area" and that other pilot's could hear the sound over the airplane's radio. The pilot reported that the engine lost power about 20 seconds after the "banging" noise began. The pilot stated he picked a field for an emergency landing into the wind. The pilot noted the gear collapsed on touchdown and the airplane slid approximately 150 feet before coming to a stop. A Federal Aviation Administration airworthiness inspector conducted the on-scene examination of the engine. The examination revealed the engine case was damaged near the number four engine cylinder. A subsequent teardown examination of the engine revealed the number four connecting rod cap and the connecting rod cap bolts had fractured. A portion of a connecting rod bolt was found impacted into the bottom of another piston. The number four connecting rod bolts and connecting rod cap were sent to the NTSB investigator-in-charge (IIC) for further examination. The IIC submitted the artifacts to Packer Engineering Inc., Naperville, Illinois, for a materials laboratory examination. The examination revealed that the nut on one of the connecting rod cap bolts was partially engaged. The connecting rod cap showed evidence of fatigue cracking on both the inner and outer edges of the fracture. Fracture features of both connecting rod cap bolts indicated the bolts had separated due to overload. The materials laboratory factual report is included with the docket material associated with this accident report.