How to Maintain a Main Thrust Bearing

The main thrust bearing is a simple part that is the foundation of your engine. It is important to maintain it correctly with regular inspections, lubrication and temperature monitoring.

Thrust bearings control the fore and aft movement of the crankshaft in the block. This allows the engine builder to set the correct end play for the crankshaft.

Material

When metal-to-metal contact occurs, friction increases and generates a grind that degrades the material. Bearings reduce this friction by rolling the two surfaces together.

Modern turbomachinery is required to operate at increasingly higher speeds and loads. This increased performance creates a challenging environment for fluid film thrust bearings that experience high surface temperatures and thin film thickness.

Polymer based materials offer a solution. Tests show that a PEEK lined thrust bearing can handle greater load for the same size as a babbitt-lined one under the same conditions, and can do so with lower power losses. This is due to the fact that PEEK can support shear and axial loads as well as radial load. It also withstands higher shear loads than a conventional ball-type thrust bearing. Moreover, PEEK is less sensitive to contamination and can support significantly higher load-carrying capacity at start up. These benefits make the bearing more cost effective.

Geometry

A main thrust bearing supports axial loads on machines. They have different designs and sizes depending on the machine requirements for maximum performance. They reduce the friction between moving parts in a machine and increase its speed.

Usually, they are used in vehicles to support the axial load of the helical gears. Other applications include transportation and industrial machinery. They are also found in turbines and generators, where they help to reduce the frictional load on rotors.

The geometry of a main thrust bearing consists of the thrust collar and a sector-shaped pad disc. The pads must be aligned with the shaft to ensure the formation of a continuous oil film. When the shaft angular misalignment is large, one pad may suffer from rub or high temperature, which leads to the degradation of its surface and the failure of other pads in a chain reaction. It is therefore important to minimize the initial contact angle between the pad and shaft.

Seals

A main thrust bearing must withstand forward thrust loads from a clutch, transmission or torque converter. These forces tend to compress the components of the thrust bearing, which makes a good seal necessary for longevity.

The preferred embodiment of this type of bearing uses double lip seals within its chamber to preserve grease for permanent lubrication. The bearing assembly also has a stainless steel machined stiffener that acts as an envelop for the body of the double lip seals to prevent foreign particles & pollutants from entering the bearing chamber.

Other forms of sealing used in main thrust bearings can include contact seals (which physically touch the shaft) and labyrinth seals that use a tortuous path to block air or oil migration from the shaft. Both types of seals are effective, but the contact-type creates more friction and heat than a non-contact seal, and require regular maintenance. The labyrinth seal is more efficient in terms of space utilization, but still requires occasional maintenance to replace worn elements.

Maintenance

The way a bearing is handled, maintained and lubricated makes a huge difference in its life and performance. Proper handling and maintenance procedures ensure longer bearing life, minimized downtime, and increased productivity.

When installing a new main thrust bearing, make sure the main caps are properly seated in the cap and block saddles. A simple test of crankshaft end play with a dial indicator placed against the harmonic balancer or flywheel can measure these saddle and cap seat areas. Excessive end play is a major cause of premature wear on these bearing surfaces, and also damages the fore and aft movements of the crankshaft in the block and causes connecting rods to fatigue, break or work loose, scoring the cylinder walls.

Consider flushing your main thrust bearings to remove foreign contaminates and degraded grease. Romax InSight has shown that this procedure can extend bearing life significantly compared to those that do not get flushed. The process also reduces the temperature of the bearing and prevents heaving rolling-element wear paths, preventing premature failure and expensive repair costs.