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Why Engine Thrust Bearings Fail
Often, soon after an engine rebuild, premature engine thrust bearing failure occurs. We will discuss some of the major causes of these types of failures. One of the most common causes of thrust bearing failures is the transmission torque convertor. When the overrunning clutch in a torque convertor becomes either seized or will not lock up in one direction, the stator does not provide it's normal function of directing the transmission fluid to create the proper torque multiplication required to drive the vehicle. When this happens, a large amount of the energy created is exhausted through the center of the torque convertor, creating excessive forward pressure. It is this pressure which causes the engine thrust bearing damage. When installing a new engine, it is wise to check the convertor your self, or have a qualified transmission rebuilder inspect it for over running clutch problems. Improper installation of the torque convertor in the transmission front pump can also lead to bearing failure, as well as transmission failure. Vehicles with standard transmissions may also experience this type of engine failure due to high clutch pressures, usually related to performance clutches with high spring pressures being installed. Riding the clutch can also cause thrust bearing failure on new engines. You must also ensure the clutch has adequate free play. Symptoms of damage caused by excessive external pressure on the crankshaft vary on engines due to their design differences. Small block Chev engines usually suffer catastrophic damage from excessive external pressures. In most cases the thrust bearing show signs of heavy rubbing on the thrust bearing. The most severe damage it on the other mains bearings, with the highest wear being on the center bearing, usually concentrated on the lower half of the bearing. The intermediate main bearings will have about half the wear of the center bearing, with the front and rear bearing showing little sign of problem. Big block Chev engines, due to the rigidity of their crankshaft, will usually only destroy the thrust face of the thrust bearing, causing little damage to the other mains. Engines with a center thrust bearing usually, as well as rubbing the thrust surface, will show signs of wear on the opposite sides of the crankshaft on the two intermediate bearings. I have seen cases of thust bearing failure on small block Ford engines that do not seem have an apparant cause. Upon checking the inner part of the bearing that seats in the block, signs of scraping on the bearing were noticed. This is the result of the installer trying to install the bearing in the rear location instead of the center, where the thrust bearing is located in this type of engine.
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