On August 15, 2004, about 1300 Pacific daylight time, an American 7ECA, N11037, collided with transmission wires and terrain during a forced landing near Manchester, California. The pilot/owner was operating the airplane under the provisions of 14 CFR Part 91. The private pilot, the sole occupant, was not injured; the airplane sustained substantial damage. Visual meteorological conditions prevailed for the personal flight, and no flight plan had been filed. The local area flight originated from Little River Airport, Little River, California, about 1230. In a written statement, the pilot reported that while in cruise flight the engine "exploded." He manipulated the throttle and discovered that the airplane would vibrate severely when the engine's revolutions per minute (rpm) increase above 1,500. He maneuvered the airplane in a gliding configuration and selected a field to execute a forced landing. As the airplane approached the field, on the pilot's predetermined final approach, the pilot noticed transmission lines in the immediate flight path. The airplane collided with transmission lines and continued to descend toward the field. Upon touchdown, the airplane hit hard, coming to rest 500 feet from the initial impact. During a telephone conversation with a National Transportation Safety Board investigator, the pilot reported that while the airplane was being recovered, he noted that the top spark plug was missing from the right rear cylinder [the number one cylinder] and observed several loose ignition leads on the cylinders. The pilot added in his written statement that the engine had undergone an annual inspection 1.97 hours prior to the accident; the engine had accumulated 58.8 hours since the remanufacture preformed by Continental Motors. The pilot thought that the accident could have been prevented if the spark plug had been tightened or properly torqued.