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.
