BEARING 2990826 - Caterpillar

(3XF),
G3618 (4WF),
G3612 (1YG),
G3616 (4CG) ENGINESProblem:
There have been some recent reports of cracking of the 7C-5044 Cylinder Liner in 10.5:1 compression ratio applications. The typical crack starts near the top flange of the liner and then propagates down along the liner sidewall. The cracked liner can result in a coolant leak into the cylinder. The following is a description of the most likely sequence of events for a cracked cylinder liner:Compression gases leak into jacket water coolant systemResults in increased jacket water temperature and pressureCoolant displaced through vent line in expansion tankCoolant leaks into the combustion chamber and/or engine crankcaseCan cause cylinder misfireHydraulic lock of leaking cylinder during crankingThis is considered a "soft" failure modeThe fire ring will most likely fail during this eventSolution:
In order to isolate a particular cylinder that is suspected of a having cracked cylinder liner, conduct the following checks:1. Pressurize the jacket water cooling system to 50-60 psi. Do not exceed a maximum allowable cylinder block pressure of 67 psi.2. Crank the engine with the spark plugs removed. Look for indications of coolant in the spark plug well.3. With the jacket water cooling system under pressure, use a borescope to check for leaks.4. Visually inspect the cylinder liners through the crankcase doors. It is possible that the crack may seal itself after the engine is stopped. Therefore, some time may be required at pressurized conditions before a leak will be found. The engine crankshaft might have to be turned to move the piston out of the way. Ensure that the bearings are properly prelubed.If it is confirmed that a cracked cylinder liner exists, then that cylinder liner should be replaced. The cracked cylinder liner should be returned to the local dealer for coordination of a thorough failure analysis by the factory. All engine related information should also be sent with the cracked cylinder liner. This includes such information as engine serial number, engine/liner hours, and customer name.In order for the factory to continue evaluating field hardware, please communicate scheduling time frames for upcoming top end overhauls. Considerations for complete inspection of all cylinder liners should also be given when replacing a failed liner. Contact the factory for additional instructions, if necessary.COPYRIGHT 2001 CATERPILLAR ALL RIGHTS RESERVED