GY6 CVT Transmission

The scooter’s automatic transmission system is based on a belt and variator driven by pulleys and weights. This system is widely known as the CVT or Continuously variable transmission.

As the force of the revolutions of the engine increase, weights known as “rollers” inside the variator place pressure against a plate, pushing the two plates close together and pushing the belt known as the V-Belt to tension higher, working similar to gears on a 24 speed bicycle.

Maintaining and “tuning” your CVT transmission will ensure you enjoy riding your scooter. Roller weights, belt, and clutch are items requiring routine replacement. “CVT Tuning” involves adjusting roller “weights” to different weights, changing CVT pulley plates to change the “pitch” or angle the belt raises, clutch springs to change the tension in order to adjust at what RPM the “clutch” engages, and the type of clutch as racing clutches engage faster. Clutches differ from one another by the material of the shoes, how many shoes, and tension springs within. Belts can be replaced with Kelvar belted materials to reduce belts from braking. There are other options such as lightening materials within the transmission as well. The following information provided below is to give users an idea of how to maintain their CVT transmission.


 Important Points

  • This chapter is about the driving unit, the clutch/driven unit and the starting lever.
  • The work on them can be done on the engine, without the disassembly.
  • The surface of the driving belt and the drive units are not allowed to have oil adhering to them. If there is any, remove it to minimize the slip between the belt and the drive units.


Torque Specifications:

  • The nut of the driving plate 3.8kg/m 28ft lbs
  • The nut of the clutch housing 5.5kg/m 40ft lbs 
  • The bolt of the driving plate 0.3kg/m 40in lbs
  • The nut of the clutch/driving plate 0.45kg/m 40in lbs


The motorcycle won’t move even though the engine runs.

  • The driving belt is worn or broken.
  • The driving pulley plate may be damaged or worn.
  • The rear brake cable may be damaged and locked.
  • The spring on the clutch may be broken and preventing the clutch from engaging.

Sudden brake tension during riding

  • Possible damage of brake cable.

Power can’t develop fully

  • The driving belt is worn
  • The clutch spring may be worn or broken.
  • The rollers are worn
  • The driving pulley plate surface is dirty

General Tools Needed:

  • Universal stand

Specialty Tools Needed:

  • Clutch spring compressor.
  • 39mm Socket CVT nut.
  • Bearing driver

Detaching the Left Crankcase Cover


  1. Unlock the clip for the air tube for the driving belt.
  2. Remove eight bolts and then take off the left crankcase cover and the locating pin.
  3. Check whether the gasket is damaged or fractured.

Removing the Starting Pivot

  1. Remove the starting lever from the pivot.
  2. Remove the retainer and the washer from the starting pivot.
  3. Turn the starting pivot gently and remove the driving gear and the friction spring together.
  4. Remove the starting pivot and the return spring.
  5. Detach the starting pivot sleeve.


Checking the Starting Pivot100a

  1. Check if the pivot and the gear are worn. Check if there is any softness of the starting return spring. Check if there is any excessive wear on the pivot sleeve.
  2. Check if the driven gear is worn or has failed. Check if the friction spring is worn or fractured.
  3. Check if there is any excessive wear on the bearing part of the starting pivot and of the shaft of the driven gear. Replace any parts showing excessive or unusual wear.

Installing the Starting Assembly


  1. Install the starting pivot sleeve and the return spring to the crankcase cover
  2. As shown in the picture on the right, assemble the driven gear and the friction spring. Maintain the orientation as shown.
  3. Install the starter pivot (3a). Install the washer, then the retainer (3b).

Assembling the Left Crankcase Cover

  1. First, install the locating pin, then the gasket.
  2. Assemble the left crankcase cover, and then tighten the eight fix bolts diagonally. Install the air tube together, and then install the retainer.101D

Checking tfle Driving Belt102a

  1. Detach the left crankcase cover.
  2. Check if the driving belt is cracked, frayed, or if there is abnormal wear. Measure the width of the belt. Maximum service allowance: 17mm (. 7 in.).

Replacing tfle Driving Belt

  1. Remove the eight fix bolts, then remove he crankcase cover.
  2. Remove driving pulley. Use a retaining device to hold the driving pulley and screw out of the 10mm (.39 in.) bolt.
  3. Remove the driving pulley.
  4. Remove the driving belt from the clutch driving pulley.102b

Assembling the Driving Belt103

  1. Turn the driving pulley clockwise to keep the notches of the belt in expanded condition. Then install the new driving belt.
  2. Install the driving belt on the driving pulley. Install the driving pulley, the starting ratchet and 10mm (.39 in.) washer. Then install and tighten the nut. Torque: 3,8kg/m 28ft lbs

34bAttentionDuring assembly, be sure to align the splints of the driving unit with those on the crank shaft with the ratchet.

The Driving Pulley-Dismounting

  1. Use a retaining device or spanner wrench to hold the driving pulley.
  2. Screw out the 10mm (.39 in.) nut, and then remove the ratchet, the l0mm (.39 in.) nut and the driving pulley.

Taking the Driving Pulley Apart

  1. Remove the driving pulley and the sleeve from the crankshaft.
  2. Remove the retainer.
  3.  Remove the rollers.

Checking the driving pulley

  1. Check the wear of the rollers. 104Measure the OD of the roller.
    • Maximum service allowance. Replace when it is below 12.4mm (.47 in.).
  2. Check the wear of the driving pulley sleeve. Measure the OD of the moving section of the sleeve.
    • Maximum service allowance: Replace when it is below 33.94mm (1.37 in.).

Driving Pulley105a

Install the driving pulley sleeve and the driving pulley on the crankshaft (la). Install the driving belt on the crankshaft (lb). Install the driving pulley and the washer (lc).

  • Tighten 10mm (.39 in.) nut.
  • Torque: 3.8kg/m 28ft lbs

Attention: There mustn’t be any grease on the surface of the driven belt and the driving pulley.

The Overrunning Clutch (Starter Pinion)


  1. Remove the left crankcase cover .
  2. Remove the driving pulley.
  3. Remove the seat of the overrunning clutch.
  4. Remove the overrunning clutch.

Checking and Assembling

  1. Check if the bearing part of the overrunning clutch shaft is worn.
  2. Check if the clutch runs smoothly.
  3. Check the wear of the gear and the bearing part of the shaft
  4. Coat the bearing part of the clutch shaft with a bit of grease.
  5. Assemble it in the opposite sequence of removal.105b






The Clutch/Transmission Pulley106a

Removing the Clutch/Transmission Pulley

  1. Remove the driving pulley. Then use a spanner wrench to hold the clutch housing to screw out the 10mm (.39 in.) nut.
  2. Remove the clutch housing. Remove the clutch/transmission pulley. Remove the driving belt from the clutch/transmission pulley.


Disassembling the Clutch/Transmission Pulley106c

  1. Use a spring compressor for the clutch spring to press down the transmission pulley spring to remove the special nut (28mm, 1.102 in.).
  2. Remove the clutch spring.
  3. Remove the sealing cover of the shaft collar.
  4. Remove the guide rolling pin from the transmission pulley assembly, and then take out the o-ring and the oil seal.


Checking the Clutch Transmission Pulley107


  1. Check the wear of the clutch housing.
      • Measure the ID of the clutch housing.
      • Maximum service allowance:
      • Replace when it goes beyond 107.5mm (4.23 in.).
  2. Check the wear of the clutch lining.
      • Measure the thickness of the lining.
      • Maximum service allowance:
      • Replace, when it is below 2.0mm (.078 in.).
  3. Measure the free length of the transmission pulley spring.
      • Maximum service allowance: Replace when it below 92.8mm
  4. Check the wear of the transmission pulley. Measure the OD of the pulley.
      • Maximum service allowance:
      • Replace when it is below 19.97mm (.79 in.).
  5. Check the wear of the transmission pulley. Measure the ID of the pulley.
      • Maximum service allowance:
      • Replace when it goes beyond 24.24mm (.95 in.).
  6. Check if the guide rolling pin is excessively worn or unevenly worn.
      • Replace as necessary.

Replacing the transmission pulley and the bearing108

  1. Check the needle bearing for wear or excessive free play, gritty feel or noise. Replace as necessary.
  2. Check the housing bearing for wear. Remove the retainer and take out the housing bearing.
  3. Drive in the new housing bearing, keeping the lid side up.
    • Attention: Grease new bearings when installing. Grease able to resist > 230″.
  4. Drive in the new needle bearing, keeping the “mark” side up.

The Clutch/Transmission Pulley Assembly

  1. Assemble the transmission pulley guide pin and oil seal.
  2. Install the sealing cover of the collar.
  3. Assemble the transmission pulley disk and the spring to the clutch assembly, pressing down with the spring compressor for the clutch spring.
  4. Install the 28mm fix nut and tighten it.
    • Torque: 5.0-6.0kg,lm 3540ft lb.
  5. Assembling the clutch/transmission pulley, put the driving belt onto the clutch/transmission pulley, then onto the driving shaft.

Assembling the Clutch Housing110a

5. Use a spanner wrench to hold the housing, then install the 10mm (.39 in.) nut and tighten it.

    • Torque: 5.5kg!m 38ft lbs
    • Assemble the left crankcase cover.




General Information

  • Designated oil: SAE 90# Gear Oil
  • Filling 0.12L 4 ounces
  • Changing 0.10L 3.5 ounces


  • Bearing pulling set 12mm
  • Bearing pulling set 15mm
  • Sleeve shaft for assembling the crankshaft
  • Sleeve lever for assembling the crankshaft


  • Bearing outer race driver 3740mm
  • Bearing outer race driver 3235mm
  • Guide lever for the bearing driver 17mm
  • Guide lever for the bearing driver 15mm
  • Guide lever for the bearing driver 12mm
  • Bearing driver


The scooter doesn’t run after the engine is started

  • The transmission gear failed
  • The driving belt is worn or broken
  •  The clutch failed

Developing abnormal noise when it runs

  • The gear is worn, burnt or has damaged teeth
  • The bearing is worn and getting loose

Oil leakage

  • Too much oil
  • The oil seal is broken

Dismantling the final transmission assembly113

  1. Remove the rear brake cable.
  2. Remove the rear wheel (refer to 13-3).
  3. Remove the left crankcase cover (refer to 9-2).
  4. Remove the driven pulley of the clutch (refer to 9-5).
  5. Drain the oil out of the final transmission.
  6. Remove the bolts of the final transmission gearbox.
  7. Remove the transmission gearbox cover.
  8. Remove the gasket and the locating pin.

Detach the final transmission gearbox cover

  1. Check the final transmission assembly.
  2. Check if the sub shaft gear is worn or damaged.
  3. Check if the final transmission gear is burnt or damaged.4. Check if the bearing in the leftcrankcase and the oil seal are wornor damaged.1145. Check if the driving shaft (the main clutch shaft) and the gear are worn or damaged.6. Check if the oil seal in the bearing of the transmission gearbox cover and that of the bearing of the final gear shaft are worn or have failed.

Attention: Don’t dismantle the final transmission gearbox, except that some parts have to be replaced. While replacing the driving shaft, the oil seal must be replaced by new ones.

Replacing Bearing (on the side of the transmission gearbox cover)

  1. Use a bearing puller to remove the bearing in the final transmission gearbox.
  2. Remove the oil seal on the final transmission shaft.
  3. Drive in the new bearing to the final transmission cover.

Replacing the Bearing (on the side of the crankcase)115

  1. Remove the driving shaft (the clutch main shaft). Then remove the oil seal of the shaft.
  2. Use a bearing puller to remove the bearing in the final transmission gearbox.
  3. Drive the new bearing into the final transmission gearbox. Install the new oil seal fro the drive shaft.

Assembling the Final Gear Set

  1. First, install the drive shaft into the final gearbox. Then install the final transmission gear shaft (output shaft) to the final gearbox.
  2. Attach the sub shaft and the washer to the final transmission gearbox. Install the resin washer to the sub shaft; install the locating pin and the new gasket.116
  3. Put on the final gearbox cover.
  4. Tighten the bolts of the finalgearbox cover.
  5. Assemble the clutch/driving pulley disk (refer to 9-8).
  6. After assembling, fill the gear box with 90w gear oil (refer to 3-7).
      • Designated gear oil: SAE 90#
      • Volume of the gearbox:
      • Filling: 0.12L 4 ounces
      • Changing: 0.10L 3.5 ounces
  7. Screw up the oil screw and tighten it.
      • Torque: l.0-1.4kg,lm 8-10ft lbs
  8. Start the engine to check if there is oil leakage.
  9. Check the oil level. Replenish it with the designated gear oil when the oil is not sufficient (through the oil checking hole).




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