RcTek : Information & Resources for the Model Car Racer

Centax Type Clutches - How They Work

In response to the requests for information regarding Centax type clutches, we have put together the following article that explains the way they work and what parts are involved.

The name Centax is used by Serpent Model Cars and is used throughout this article as it has become synonymous with this type of clutch.

How the Centax Clutch Works

Centax Clutches

As mentioned in the introduction to this series of articles, Centax type clutches operate (just like any other clutch used in remote controlled model cars) by converting the centrifugal force that the speed of the flywheel generates into a movement that connects the driving force from the engine to the transmission.

The image shown below right below shows a cross-sectional view of a typical Centax type clutch assembly. All of the parts were identified in the second of this series of articles.

Basically the clutch works in this manner;

The flywheel is spun round by the engine and the flyweights (yellow) are then subjected to centrifugal force and try to move outwards.

Because of the tapered sides of the flywheel, the flyweights move up the sides of the tapers, which makes them move in a diagonal direction (both vertically and horizontally).

It is this movement that forces the clutch shoe (green) against the clutch bell (grey).

This principle will be better understood by the studying the animation to the left, in which some of the parts have been removed for clarity.

When Played, the animation shows how the centrifugal force (that the speed of the engine generates) causes the flyweights (yellow) to slide up the ramps on the inside of the flywheel and force the clutch shoe (green) sideways.

You may Stop the animation if required.

There’s More…

The description above left out the involvement of the spring (red). The purpose of the spring and its associated adjusting nut (pink) is to provide a means to control how and when the clutch shoes engage. The spring presses against the flyweights and provides resistance against them moving. If you tighten up the adjusting nut you compress (preload) the spring. It then requires more centrifugal force from the spinning flywheel to overcome the resistance of the spring to allow the flyweights to move. Conversely, if you loosen off the adjusting nut there will be less preload on the spring and less centrifugal force will be required to overcome the resistance of the spring.

When the engine speed decreases, the amount of centrifugal force also decreases to the point where force of the spring is able to return the flyweights and clutch shoe to their former position, therefore disengaging the drive to the transmission. This is helped on the Serpent clutch by the inclusion of the Spring/O-ring around the flyweights, which is shown in the first article of this series.

The spring/adjuster is not the only adjustment that can be made to how the clutch operate though. As the clutch works by the flyweights pushing the clutch shoe sideways, the amount of free play (end float) also affects when the clutch engages.

Centax clutch adjuster

The whole assembly pushes against the retaining screw in the end of the crankshaft, so if it were further away, it would have to move a greater distance before it engaged. Conversely, if it were closer to the flywheel, it would take less movement from the flyweights to engage the clutch. Adjusting this end float can be done in a number of ways, the PB Racing solution is shown on the right and uses a threaded adapter. Simply tightening or loosening the nut allows the end float to be adjusted without any disassembly.

Centax clutch shims

The same adjustment can be made to the Serpent clutch using some shims (part number 1093) like those that are pictured on the left. Many people do not use these, they alter the end float by adding and removing the shims from behind the flywheel. This long winded method is used, presumably, because there are few instructions on how to use them.

As there are two different methods of adjusting the engagement of the clutch, you can use them both to achieve different effects. A larger end float measurement gives more movement and also will yield in a harsher engagement, as there is time for a significant increase in the momentum of the flyweight/clutch shoe assembly.

Related Information

Parts Descriptions & Diagrams of Centax Type Clutches

Centax Type Clutches — Further Information

Thrust Race Bearings

How Gears Work

Centax Adjusting Tool

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© 2001, 2009 by Darren Burnhill