On March 23, 1995, at 0815 central standard time, an Aero Commander S2R, N5561X, was substantially damaged during a forced landing near Gillett, Arkansas. The commercial pilot did not receive injuries. Visual meteorological conditions prevailed for the local aerial application flight. During an interview, conducted by a Federal Aviation Administration inspector, and on the enclosed Pilot/Operator report, the pilot revealed the information in this paragraph. Upon completing the third swath and applying throttle, the engine power did not increase and the oil pressure dropped to 40 PSI. During the forced landing, as the pilot banked the airplane to the right, in order to avoid trees, the main gear collapsed as it struck the ground. Subsequently, the airplane slid into trees and the outboard 6 feet of the left wing was bent upward. The operator reported that an engine teardown was performed at Covington Aviation of Tulsa, Oklahoma. The Vice President/Chief of Covington Engines (statement enclosed) reported that the main rod bearing was plated with silver and lead; however, with a high time bearing the metal wears and pieces of the metal stop up the oil passages and the bearing seizes on the crankshaft. The operator reported that this engine had 1,549 hours since the last overhaul. The manufacture's recommended time before overhaul (TBO) is 1,200 hours. Pieces of metal were found in the oil passages, the main rod bearing was seized to the crankshaft, and gear splines were separated from the cam gear and cam gear drive.