Clutch Bell Polini EVO II d=107mm Yamaha Aerox / MBK Nitro

The function of the clutch bell

Even though the clutch bells of scooters (centrifugal clutch) and clutch baskets of motorcycles (with multi-plate clutch) look different, their function is basically the same. What changes is the way they are actuated.

On a scooter or moped with a centrifugal clutch, when the engine revs up, the clutch shoes spread and engage the clutch bell and cause it to rotate. The bell then drives the transmission, which in turn turns the wheel.
On a motorcycle or motocross bike with a multi-plate oil bath clutch, the lined clutch plates engage the plain metal plates, which in turn drive the bell to rotate the transmission and wheel. When the clutch is actuated, the lined discs no longer engage the plain discs and rotation comes to a halt.

In short, the bell ensures that rotation is transferred from the engine to the gearbox and wheel.

Clutch bell: performance

With a tuning clutch bell, it is possible to improve performance or reliability.

Choosing materials like steel instead of aluminum provides greater durability. The heavier weight of steel also leads to higher inertia, which in turn can lead to higher torque. This is the case with the Hinson Momentum bell, for example.
A bell can also have cut-outs to improve cooling and thus prevent wear. Therefore, on scooters, you often find ventilated racing clutch bells. Also in motocross, some clutch bells have more cut-outs than others.

In summary, the weight and ventilation of a clutch bell affect the overall performance of the engine.

How to replace a clutch ?