On April 1, 2011, about 1635 Atlantic Standard Time, a Cessna 172P, N98FR, experienced a loss of engine power and force landed on a closed, abandoned airfield near Vega Baja, Puerto Rico. The airplane was substantially damaged. The airplane was registered to Flight World, Inc. and was operated by Isla Grande Flying School under the provisions of 14 Code of Federal Regulations Part 91 as a personal flight. Visual meteorological conditions prevailed and no flight plan was filed. The private pilot and two passengers were not injured. The flight originated from Borinquen, Puerto Rico (BQN) about 1600 and was destined for San Juan, Puerto Rico (SIG). The pilot reported that the airplane was in cruise at 1,000 feet above ground level when the engine lost power and began to vibrate heavily and the altitude could not be maintained. About 250 feet, he observed a runway at a closed, former military base and attempted a landing. During the landing attempt, the airplane collided with trees and bushes. Structural damage to the wings and fuselage resulted. Initial examination of the engine by a Federal Aviation Administration inspector revealed that the number 2 cylinder exhaust valve spring was loose. The cylinder was subsequently examined and the exhaust valve, manufactured by Superior Air Parts, was found to have failed. The operator reported that all of the exhaust valve parts, with the exception of the valve keepers and associated parts, exited the exhaust system. The exhaust valve reportedly had accumulated about 1,120 hours since installation.