TM 10-3930-671-24 L. Engine Knocks & Noises Combustion Knocks (Excessive) 1. Overloading (’Lugging’) Reduce load or increase speed. 2. Poor quality fuel Use only No. 2 diesel engine fuel oil for best performance and economy. 3. Injection timed too early Follow recommended timing procedure. 4. Injection nozzle sticking Remove nozzle, check opening pressure, clean and adjust. Mechanical Knocks 1. To locate knock “Short out” cylinders by loosening fuel line to nozzle one at a time. If no change in sound, knock is not occurring in that cylinder. 2. Main bearings Heavy, dull knock when accelerating under load. Examine bearing lining for wear or excessive clearance. Replace, as necessary. 3. Connecting rod bearings Noise appears at idle or light load and disappears at full load. Overhaul engine. 4. Loose piston pin Sharp metallic rap at idling speed or when starting cold. Replace pin with oversize. 5. Broken piston ring or pin Sharp, clicking noise that cannot be eliminated by shorting out. Remove pistons, and replace piston pin or rings, as necessary. 6. Tappet noise Check clearances; adjust to specifications. 7. Timing gear noise Loose or worn gears rattle. Check gear fit and examine teeth. Refit new set of gears if loose or worn badly. F-72