RcTek : Information & Resources for the Model Car Racer

The Parts of Thrust Race Bearings & How They Work

Thrust race bearings are a special type of bearing that are used in remote controlled model car clutch systems and are usually three part assemblies.

This article shows the various parts and different versions available and then goes on to explain possible solutions to problems that may be encountered.

Basic Explanation

Thrust Race Bearing

Thrust race assembly

Thrust race bearings are designed to bear axial loads, that is, a load that is perpendicular (at 90 degrees) to the shaft it is mounted to. This is necessary for the Centax type clutches used on the high performance remote controlled model cars we have today. We have further information about this type of clutch in our Centax Clutch series of articles.

Different views of a thrust race bearing are shown to the left right and the right. The outer parts are the bearing races and are usually made from hardened chromed steel. The inner part is composed of the bearing cage, which is usually made of brass, and the actual ball bearings.

Types of Thrust Race

Thrust race bearings

Thrust race bearings

There are two variations of thrust race used on model cars and the differences lie in the way that the cage is manufactured.

The image on the left shows the first type of cage, which is manufactured by pressing thin brass sheet into a shape that holds the bearings in place. Whilst this is light in weight and is an inexpensive solution for the manufacturer, it can cause premature failure problems when used with large end float values. See below for details.

The image on the right is made using a solid cage into which the ball bearings are set using a press. This is both heavier and more expensive to make, but suffers a substantially lower failure rate when used with large end float values.

Detailed View

Thrust Race Bearing Cross Section

Thrust Race Bearing Cross Section

Both types of cage are shown in the accompanying diagrams and the arrows are there to show the effect that centrifugal force will have on the ball bearing when it is being rotated.

The image on the left shows the solid version of the cage and you can see that it does a good job in controlling the outward movement of the ball.
The pressed version of the cage is shown on the right and you can see that there is only a thin metal lip that controls the ball from being thrown outward.

Large End Float Values

Thrust Race Bearing Cross Section

Thrust Race Bearing Cross Section

As the centrifugal force is concentrated on the outer races of the bearing, they will both perform in the same way while the end float (the gap between the outer races) remains small.

The advantages of the solid version become clear when large end float values open up the gap between the outer races. The solid version has the strength to withstand the force of the ball bearing being thrown outward by the centrifugal force, where as the pressed version doesn’t.

The diagram on the left shows the pressed version with a very small end float value. In the image on the right though, you can see what happens when the end float increases. The thin lip of the cage is forced outwards as it isn’t able to withstand the centrifugal force of the balls.

What usually happens with this type of caged bearing is that the bearing falls apart when the clutch is disassembled for maintenance. Alternatively, the bearing can disintegrate whilst the car is moving and lock the clutch up completely.

Maintenance

Thrust race bearings require very frequent lubrication because any grease etc. you apply will be subject to centrifugal force and will be thrown away from the place where it is needed. If your clutch bell has a dust cap, fit it, it will stop the grease disappearing too quickly.

Some cars, such as the Serpent ones, have an adjustment hole in the clutch bell that provides a good escape route for the grease. You could consider using a thin O-ring around the clutch bell to cover this hole.

Summary

The thrust race bearings used in the clutches of the remote controlled model cars of today don’t seem to be available in both cage types, so you may be unable to get the type that would be better.

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© 2001, 2009 by Darren Burnhill