On September 28, 1995, at 0930 central daylight time (cdt), an Ercoupe 415-D, N89331, piloted by a private pilot, sustained substantial damage during an attempted forced landing when the aircraft hit a powerline and subsequently struck the terrain. Visual meteorological conditions prevailed at the time of the accident. The flight was operated under 14 CFR Part 91. A flight plan was not on file. The pilot reported minor injuries. The flight departed St. Charles, Missouri, at 0900 cdt and was en route to Belleville, Illinois. The pilot reported that his engine lost power while cruising at 1700 feet above ground level. "There was an abrupt change in sound and the rpms dropped from 2450 to zero." He indicated that prior to the engine quitting, there were no indications of a problem. The pilot made two attempts to restart the engine with no success. At this time, he realized that he was losing altitude. The pilot picked out a corn field one block north of a highway and along side a major road and began a forced landing. On approach to the field, the landing gear of the airplane caught some high tension powerlines running parallel to the road. The airplane snapped through three of the lines, pitched down, struck the road and slid approximately 30 feet before coming to a stop. The Federal Aviation Administration (FAA) inspector who examined the wreckage reported finding oil streaked down the right side of the fuselage beginning just aft of the engine cowling and running to the tip of the tail. Upon closer examination of the engine inside the cowling, a line connecting the engine to the cockpit oil pressure gauge was found to be covered in oil and was spongy to the touch. The engine was examined by FAA inspectors at Ben Emge Airport, Belleview, Illinois, on October 4, 1995. A rubber oil pressure line running from the number one cylinder to the firewall was removed to check for damage. When submerged in water and air blown through the line, the line revealed a small hole. The number 3 spark plug and valve cover were removed. The spark plug showed no damage and appearance of normal burning. The engine was pulled through to see the valves operate. The number 1 and number 2 intake valves were stuck in the open position. The intake valve on the number 1 cylinder was staked to see if the valve would close and it did. The engine was pulled through again and the valve stuck open again. The number 2 intake valve also stuck open. Examination of the valves showed signs of inadequate lubrication.