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Tech Tips & Information
The TKM Clutch

The TKM Clutch
By C D Compton

The TKM clutch is a centrifugal clutch, which engages at about 6000 rpm. Many karters are unfamiliar with clutches and many drivers believe that they will reduce performance. The author has found that since fitting a clutch the practice lap times have not changed, but positions have improved. The driver explains this as being due to having increased courage going into contended corners.

1. How the Clutch Works

Figure 1-1 Disengaged Clutch

When the engine is at rest or rotating at less than 500 rpm, springs pull the Pressure plate back towards the Drive Hub and away from the Friction disc.

Figure 1-2 Driving Clutch

When the engine runs it rotates the Drive Hub, Fixed Plate and Pressure plate Assembly. The Levers are weighted and have a cam shaped face, which rests against the Pressure Plate. As the engine accelerates above 6000 rpm, the levers rotate outwards under centrifugal force so that the cams force the Pressure Plate against the Friction Disc (clamping the friction disc between the Pressure Plate and the Fixed Plate). The Friction Disc drives the Sprocket Drum via the tabs on the circumference of the Friction Disc, which fit, into the slots in the back of the Sprocket Drum.

2. After each Event
The clutch should be cleaned, checked and the sprocket drum roller bearing re-greased after each event. This can be done with the engine still mounted in the kart.

3. Removing the Clutch
Removing the clutch from the engine is a simple procedure, which does not require any special skills. It does however require the following special tools;

The clutch can be removed whilst the engine is mounted in the kart, but it is easier to work with the engine on a bench.

4. Dismantling the Drive Hub Assembly

[Figure 4-1] The Drive Hub Assembly


Three counter sink hex' socket screws which secure the Fixed Plate (B) to the Drive Hub (G).


Fixed Plate.


Friction Disc.


Pressure Plate.


3 x sets of three Levers.


3 x Dowel Pins.


Drive Hub.


3 x Pressure Plate Springs.


3 x Spring Retainer Nuts.

5. Check and Clean the Components
Clean all of the clutch components using spray Brake Cleaner. (This will remove all grease from the roller bearing!)

5.1 Checking the Friction Plate
Remove the friction plate and inspect it for impact damage and cracking.

Figure 6.5-1 Impact Damage

6. Reassembling the Drive Hub
Ensure that all parts of the clutch are clean and that minimum amounts of grease are used. Under no account allow grease, oil, WD40 or any similar contaminant onto the Friction Disc or the ground surfaces of the Pressure Plate and Fixed Plate.

Figure 6-1 Pins and Levers in place
Figure 6-2 Springs and Retaining Nuts
Figure 6-3 Checking the Spring Retension Nut Height

7. Re-fitting the Clutch

[Figure 7-1] Coned Safety Washer

Figure [7-2] Sprocket Drum & Bearing

If you tighten the starter nut with the Sprocket Drum slots not engaged with the Friction Disc tabs so that the Sprocket Drum is pressing on the Friction Disc tabs then you might crack the Friction Disc.

9. Sprocket Drum Clearance
If you have not changed the Sprocket Drum or the Thrust Washers then the Sprocket Drum clearance should be OK. If the end float is much less than expected then you have assembled it incorrectly! To measure the Sprocket Drum clearance, use a feeler gauge. Check the free play and adjust it by changing the thickness of the Internal Thrust Washer.

This article was produced by Chris Compton, author of "A Practical Mechanicís Guide to TKM Karting " which is available from

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