RcTek : Information & Resources for the Model Car Racer

Centax Type Clutches — Parts Descriptions & Diagrams

In response to the requests for information regarding Centax type clutches, we have put together a series of articles that explain the way they work and what parts are involved.

Please note that I only have knowledge of the Serpent and PB Racing products, so cannot cover all possible variations of this type of clutch. The PB Racing variant of the Centax clutch is used throughout this article with the Serpent differences noted.

The Parts

As you can see from the exploded diagram below, there are quite a few parts involved in a centax type clutch, which are introduced below. Please note that this type of clutch is only available for engines with the SG type crankshaft.

Centax clutch assembly with engine Retaining Screw and Spacer Thrust Race Clutch Bell Clutch Bell Bearings Adjusting Nut & Spring Spring Cup, Clutch Shoe & Stabilising Plate Spring/O-ring & Flyweights Flywheel & Nut Flywheel Cone & Shims

Click on the number on the drawing for more information about the corresponding part.

1. Retaining Screw and Spacer

Centax Clutch Parts

The clutch bell assembly is held in place on the Serpent Centax clutch by an M3 Allen cap set screw, although other manufacturers have an adjuster instead.

The Serpent one can be adjusted using shims (part #1093) The spacer maintains any end float necessary for the thrust race/clutch bell assembly.

2. Thrust Race

Centax Clutch Parts - Thrust race bearing

Because of the way that this type of clutch operates, a special kind of bearing is required that will take an axial (sideways) force. The PB Racing one was far bigger and able to take the generated forces than any other I have seen.

There is a modification that was tried using normal bearings and this is covered in the third article in this series. We also have a separate article about Thrust Race Bearings.

3. Clutch Bell

Centax Clutch Parts

There isn’t a great deal to say about the clutch bell, apart from the fact it is dished to match the shape of the clutch shoe. It has to be noted though, that with the Serpent system, the gears are separate to the main clutch bell and can be changed independently of each other. More information about gears can be found in our How Gears Work article.

4. Clutch Bell Bearings

Centax Clutch Parts

Flanged Bearing

The clutch bell bearings are there to support the radial load on the gears and allow it to run freely when the clutch is not engaged. Both plain bearings (left) and flanged bearings (right) are used in Centax type clutches, with either two or three bearings being used due to the size limitations imposed in the design of 1/8th and 1/10th scale cars.

5. Adjusting Nut & Spring

Centax Clutch Parts

Centax Clutch adjusting nut

These two items are fairly easy to understand, the nut is used to adjust the preload on the spring to alter when/how the clutch engages. The image on the right shows the Serpent adjusting nut.

For further information about an adjusting tool for the Serpent clutches, please see our Centax Adjusting Tool article.

6. Spring Cup, Clutch Shoe & Stabilising Plate

Centax Clutch Parts

The spring cup is necessary to stop the spring wearing its way through the soft material of the clutch shoe, which is usually made of PTFE.

The stabilising plate does just as its name suggests in controlling the alignment of the flyweight/clutch shoe assembly.

7. Spring/O-ring & Flyweights

Centax Clutch Parts

Centax Clutch Parts

The flyweights (which can also be made of PTFE) are the parts which provide the means for the centrifugal movement to be transferred into an axial movement. The spring or, as is sometimes used, O-ring is used (on the Serpent version - left image) to help the flyweights return to a position where the clutch can disengage quickly.

The PB Racing version (right image) relied on the main spring in the clutch to return the shoes.
This area of the clutch is where there are major differences between the centaxial clutches from the different manufacturers. Some use cone shaped wedges and some use levers.

8. Flywheel & Nut

Centax Clutch Parts

Centax Clutch Parts

The PB Racing (left) and Serpent flywheel (right) are basically the same, except that the PB one used a separate ramp ring made from PTFE for the flyweights to move up and down.
The nut is basically the same between these two manufacturers.

The flyweights and nuts in the clutches from other manufacturers will obviously be different, depending on the system they have adopted for transferring the centrifugal movement into an axial one.

9. Flywheel Cone & Shims

Centax Clutch Parts

The flywheel cone acts as an accurate means to centralise the flywheel onto the crankshaft of the engine. The shims are used to set the distance of the flywheel from the end of the crank so that the correct amount of end float (free play) can be set for proper operation of the clutch.

Related Information

How the Centax Type Clutch Works

Centax Type Clutches — Further Information

Thrust Race Bearings

How Gears Work

Centax Adjusting Tool

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© 2001, 2009 by Darren Burnhill