Home mechanic (basic tools) ยท Time: 45 to 90 min (estimate)
An automatic scooter has no gears. A rubber belt runs between two pulleys whose sides move in and out. The front pulley (the variator) sits on the engine crankshaft; the rear pulley sits on the clutch. As revs rise, rollers in the variator push the front pulley halves together so the belt rides higher, which works like a higher gear. A worn belt gets thinner and slips, so the scooter revs but is slow, and in the end it breaks. The K-Light 125 has a manual gearbox, so this page uses general principles and two cited workshop guides. For widths, torques and part numbers, follow your scooter's manual.
Safety
- Let the engine and exhaust cool. The drive case and exhaust burn skin.
- The variator nut is very tight. Use a proper holding tool that cannot slip; a slipping tool cuts hands.
- Keep oil and grease off the belt and the pulley faces. Even a fingerprint of grease makes the belt slip.
- A belt that breaks while riding can stop the rear wheel driving suddenly. Do not ride on a cracked belt.
You need
- The correct belt for your model (check the part number or the size printed on the belt).
- A variator holding tool, sockets, a torque wrench and your manual's torque for the variator nut.
- A vernier caliper to measure belt width; brake cleaner and clean rags.
Steps
- Put the scooter on the centre stand. Remove the air duct and any parts covering the drive case (on some models the exhaust or kickstart lever).
- Remove the drive case cover bolts. Note bolt lengths. If the cover will not come off, check for a missed bolt; do not lever it.
- Look before you clean. A lot of black rubber dust means the belt is wearing fast. Oil or grease inside the case means a leaking seal; find it before fitting a new belt (Oil leaking from the scooter rear gear case).
- Inspect the belt: reject it if cracked, frayed, glazed, missing teeth, oily or stiff.
- Measure the belt width in several places and compare with your manual's minimum width.
- To remove the belt, hold the variator with the tool and undo its nut. Pull off the outer pulley half carefully, keeping the inner parts in place unless you are servicing the rollers (Check variator rollers and sliders).
- Push the belt down into the rear pulley to open it, and lift the belt off.
- Clean both pulley faces with brake cleaner. Look for grooves, steps or blue heat marks. Grooved faces wear new belts quickly and need replacing.
- Fit the new belt with any arrow pointing in the direction of rotation. Push it deep into the rear pulley so it sits low at the front.
- Refit the outer variator half. Make sure the belt is not trapped between the variator halves or on the boss. Tighten the nut to your manual's torque.
- Turn the rear wheel or engine by hand a few turns so the belt climbs to its normal position.
- Refit the cover (new gasket or O-ring if fitted), duct and other parts.
Check your work
- The scooter pulls away smoothly and accelerates normally.
- No squeal or new noise from the case.
- Recheck that nothing was left inside the case.
If it did not fix the problem
- Still slips: Scooter revs but accelerates slowly; check the rollers and the clutch (Check the scooter clutch and bell).
- New belt wears out fast: check pulley faces, rollers and oil leaks.
Replacement intervals vary by model. One parts maker's guide gives roughly 10,000 to 30,000 km depending on engine size; use the interval in your owner's manual.