The clutches centrifugal type are characteristic of motorcycles with automatic transmission . The main characteristic of centrifugal clutches resides in that in their resting state they are disengaged, otherwise than the multi-disc clutches , and the clutching work is carried out automatically, without any type of actuation command.



Centrifugal clutch operation

The centrifugal clutch is composed of a shoe-holder plate, where there are some shoes that contain a gasket used as a friction element, and are kept closed at rest by the action of a set of clutch springs. These shoes pivot on lugs located on the shoe-holder plate to cause contact between the shoes and the clutch bell by means of centrifugal force, thus transmitting the movement of the motor to the wheel.


The clutch and its casing move individually when the vehicle is stopped and at idle , the centrifugal clutch being connected to the movement of the variator, integral with the crankshaft, through a V-belt. The clutch bell is integral with the secondary transmission, which drives the wheel, so it does not receive the movement of the engine unless the centrifugal clutch acts.


This is one of the reasons why we cannot start pushing a motorcycle with centrifugal clutch, since the movement of the wheel will cause the rotation of the clutch bell, but not the movement of the centrifugal clutch and, as a consequence, the movement of the crankshaft.


Upon receiving the movement of the motor, the clutch begins to rotate and, through the action of the centrifugal force, the shoes tend to overcome the resistance offered by the clutch springs, in such a way that they separate towards the outside of their rest position and end up rubbing against the inner face of the clutch bell.


This friction causes friction drag of the bell , and since it is linked by a spline to the final drive shaft, the rotation will eventually reach the rear wheel. From a certain engine rotation regime, the centrifugal force will be sufficient to prevent any slippage between the shoes and the casing, with which the rotation of both parts will be totally united.


What are the most common failures in centrifugal clutches?

The most common faults in a centrifugal clutch appear in the shoes, in the clutch bell and in the clutch springs:


The clutch shoes suffer from the wear of their packing during their useful life, so the thickness of the latter is checked and if it shows a wear greater than that specified by the manufacturer, we must replace them with a new set of clutch shoes.

Sometimes, because they are components exposed to high temperatures, the padding of the brake pads crystallizes, losing adherence and their skidding appears on the clutch bell. If the shoes show crystallization, their surface can be gently sanded with fine-grained paper in order to return them to their original state and improve their performance.

The clutch bell also suffers wear on its inner race, which is where the centrifugal clutch shoes act. The track must not present any marks and it will be checked that its minimum diameter is that specified by the manufacturer. Excessive temperature, or excessive slippage, causes deformation of the bell and poor transmission of engine power. This deformation of the bell is usually accompanied by the appearance of blue or brown tones on its surface, which indicate an excess of slippage of the set of shoes.

The clutch springs must not be deformed and their anchors must be in perfect condition. Fatigued or defective springs will cause excessive slippage and drag of the rear wheel when the shoes contact the bell with the engine at idle, and must be replaced with new ones with the same characteristics to restore normal operation of the centrifugal clutch system. .

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