On June 7, 2018 about 1100 eastern standard time, an experimental amateur-built Vans Aircraft RV-4, N7765X, was substantially damaged during a forced landing shortly after takeoff from Pittsburgh/Butler Regional Airport (BTP), Butler, Pennsylvania. The private pilot sustained minor injuries. The personal flight was operated by the pilot under the provisions of Title 14 Code of Federal Regulations Part 91. Visual meteorological conditions prevailed, and no flight plan was filed for the local flight. According to the pilot, after takeoff from runway 26 at BTP, while flying on an extended crosswind traffic pattern leg about 800 ft mean sea level, the engine lost total power. He subsequently continued ahead, maintained best glide speed, and landed in a field. During the landing, the airplane impacted a wire fence and brush. The fuselage and wings sustained substantial damage. The pilot further reported that that this was the first flight after maintenance repairs he had performed to the airplane's automobile-converted engine, due to a prior engine failure that occurred about one month earlier. During the repair, he replaced all four pistons on the engine. He also stated that he had installed an "aftermarket ECU [engine control unit]," and modified the fuel delivery software to lean the fuel to air mixture for improved engine starts. In discussing the engine failure that occurred during the accident flight, the pilot stated that the "cause of the engine failure was my entering a bad tune which caused the engine to run lean under high load. Detonation occurred and caused a piston to melt halting the engine." According to a Federal Aviation Administration inspector, the pilot reported that he had previously "burnt through a piston" with this engine during flight. The pilot also reported that during the run-up on the day of the accident, the engine was "not as strong" as it should had been, but he decided to fly anyway. The pilot held a private pilot certificate with a rating for airplane single-engine land. He also held a repairman experimental aircraft builder certificate, limited to inspection of the accident airplane. He reported total flight experience of 420 hours and 90 hours in the accident make and model airplane. His most recent Basic Medical requirements were completed in June 2017. His most recent flight review was in July 2017. The two-seat, low-wing, fixed landing gear, single-engine airplane was manufactured in 2015. It was equipped with an automobile converted, fuel-injected, General Motors Ecotec L61, 142-horsepower engine. The weather conditions reported at 1056 at BTP, included variable wind at 3 knots, visibility 10 statute miles, clear skies, temperature 17°C, and dew point 10°C.