Torque Spring Polini Evolution 4,7mm Piaggio

Contra spring

The contra spring, or torque spring is part of all scooters and mopeds with CVT transmissions.

function of torque spring

The contra spring is located between the rear pulley and the clutch. As soon as you accelerate and the engine revs up, the spring is released by centrifugal force. This causes the front pulley to open, which in turn causes the V-belt to move outward on the CVT front pulley. The transmission ratio changes in favor of higherspeed. When the scooter slows down and the engine speed is reduced, the torque spring is compressed again and the V-belt returns to a lower position on the front pulley.

soft or hard contra spring?

The choice of torque spring depends on different engine components, you need to find the right balance here.

• A spring that is too hard cannot fully expand. Acceleration is improved, but the V-belt cannot move outward to the maxi and top speed will be lowered.
• A spring that is too soft will relax too quickly, affecting the pull of your scooter.

Tip: To determine whether the V-belt can move to its maximum achievable position, you can mark the maximum position with a felt-tip pen on the CVT. If the mark disappears, this indicates that the belt actually moves up to the max position, i.e. the spring is not too hard.

How to change the torque spring ?