Rollers are small round weights inside the front pulley (variator) of a scooter, in the left side case. Plastic sliders guide the ramp plate that sits over them.
What it does
As engine speed rises, the rollers are thrown outward along ramps. This pushes the moving half of the front pulley toward the fixed half, so the belt climbs to a larger radius and the gearing gets taller. Roller weight decides at what engine speed the scooter changes up. Worn rollers develop flat spots, stop rolling and slide instead, which makes the ratio change in jumps.
Signs it is worn or failing
- Jerky or uneven acceleration, rattle at idle: Noise from the drive case.
- Slow pick-up: Scooter revs but accelerates slowly.
- Low top speed: Scooter will not reach top speed.
- Judder when pulling away can also come from the clutch: Scooter judders.
When to replace it
Replace rollers when they have flat spots, uneven wear or are no longer round. Replace all rollers as a set, and the sliders at the same time if they are worn or cracked.
What to match when buying
- Size: diameter and width in mm, for example a code like 16×13. Measure the old roller.
- Weight: in grams, usually printed on the side. Use the standard weight from the manual. Lighter rollers make the engine rev higher; heavier rollers make it labour.
- Make, model and engine size. Sliders and ramp plates are model-specific.
- Avoid rollers with seams, rough surfaces or mixed weights in one pack.
Fitting notes
- Fit rollers in the direction the old ones came out if they are shaped. Do not grease them unless your manual says so; grease collects dust.
- Check the belt while the case is open.
- See Check variator rollers and sliders.