On March 19, 2010, about 1520 eastern daylight time, an experimental amateur built Ferguson FX4-2 light sport aircraft, N8508H, was substantially damaged following a forced landing near the Cartersville Airport (VPC), Cartersville, Georgia. The sport pilot/owner and certified flight instructor were not injured. Visual meteorological conditions prevailed and no flight plan was filed for the local instructional flight, which was conducted under the provisions of 14 Code of Federal Regulations Part 91. According to the pilot, the purpose of the flight was to practice takeoffs and landings at VPC. He stated that he and the instructor performed a preflight inspection of the airplane, and conducted 3 takeoffs and landings from runway 19 without incident. The pilot stated that on the fourth takeoff, the airplane lifted off as usual and everything seemed normal He stated that the engine temperatures were within the normal range. At traffic pattern altitude, the pilot reduced power to maintain 70 miles per hour (mph) and turned left to enter the downwind leg of the traffic pattern. Shortly after making the turn, the engine shut down and the instructor took control of the airplane as the pilot attempted to restart the engine. The instructor stated that the engine started and regained full power for about 5 seconds and then shut down again. He maneuvered the airplane for an off-airport landing in a pasture east of the runway. He stated that the landing in the pasture was very hard, and the airplane pivoted up on the nose cone before coming to a stop. A Federal Aviation Administration (FAA) inspector who responded to the accident site reported that there were 4 gallons of usable fuel on board the airplane. The airplane's total fuel capacity was 5 gallons. According to FAA and maintenance records, the airplane was manufactured in 2006, and had accrued 106 total aircraft hours. Its most recent annual inspection was completed July 15, 2009, at 92 total aircraft hours. The pilot held a sport pilot certificate with a valid driver's license in lieu of an FAA medical certificate. His total flight time was 73 hours, with 33 hours in the accident airplane make and model. The instructor held an airline transport pilot certificate with a rating for airplane multiengine land, a commercial pilot certificate with a rating for airplane single engine land, and a flight instructor certificate with ratings for airplane single and multiengine. His most recent first-class FAA medical certificate was issued in July, 2009. He reported 7,100 hours of total flight experience, but his total experience in the accident airplane make and model could not be determined. A detailed examination of the airplane's engine was conducted under the supervision of a FAA inspector. During a initial test run, the two-cycle engine started and ran continuously on the airframe. Later in the run, when the engine was accelerated to full throttle the engine lost power. Further examination revealed a failure of the engine-driven oil pump drive coupling. The rear piston lands over the piston rings showed thermal distress consistent with the loss of lubrication and cylinder compression was diminished.