FTW85LA194

An annual inspn had just been completed (4/22/85) & each eng had about 1 hr of flt time. The plt stated that he took off & climbed to cruise at 9000 ft, then closed the cowl flaps & set the fuel settings for 75% power. While en route, he noted oil trailing from the l eng oil access door, but the l oil pressure was in the normal range. He throttled back the left eng & requested vectors to the nearest arpt. The plt rprtd that while diverting, he saw fire coming from the aft end of the r eng compartment. The plt shut down the r eng, declared an emerg & subsequently made an emerg/gear up landing in a wet field. Drg an apch over trees to land, he had to maneuver to avoid power lines. Teardowns of both engs revealed melting on the edge & top of svrl pistons. One eng had melting in the head of 1 cylinder & its exhaust vlv seatwas damaged. No maintenance or pre-acdnt discrepancies were fnd that would have resulted in pre-ignition or detonation. There was evidence the rprtd fire was actually oil being used & ignited by the turbo-chargers.