Guide To Scooter Clutches, Variators and Rollers

When viewed from the side, one plate is convex and the other is concave. At low engine speed, the plates of the front pulley are pushed apart by the tension of the belt as it forces itself between the plates. At the same time, the plates in the rear pulley are pushed together by the spring beneath the automatic clutch.

Behind the moving plate of the front pulley, there are clutch rollers, these are thrown towards the outside edge of the variator by centrifugal force, as the rotation speed of the engine / variator increases.

When the weight rollers move towards the outside of the variator, the inside plate is forced together with the outer plate and this moves the drive belt towards the outside of the pulley. This effectively makes the diameter of the front pulley larger. As the belt moves out on the front pulley, the tension in the belt is increased, which overcomes the spring pressure holding the two plates together in the rear pulley. The belt moves towards the center of the rear pulley, which effectively makes the diameter of the rear pulley smaller.In this way, the ratio between the two pulleys is changed and therefore, the speed ratio between the engine and rear wheel is changed.

It is common for the scooter manufacturers to restrict the speed of the scooter by fitting a spacer washer under the variator. This restricts the amount the variator is allowed to open. if removed the belt is allowed to go further out into the pulley.