GY6 CVT transmission short|longcase

If you look into a planetary gearbox set, you will see a complex world of mechanical parts, such as gears, brakes, clutches, and other governing devices. Although, on the contrary, a continuously variable transmission is actually a simple study. Most of the time CVTs just have three basic components:

  • A high-power metal or rubber belt
  • A variable-input "driving" pulley
  • An output "driven" pulley

The variable-diameter pulleys are the most important part of a CVT. The pulleys are each made of two 20-degree cones facing each other. There is a belt riding between the two cones in the groove. People prefer V-Belts when manufacturer’s make the belt in rubber. The belts have a V-shaped cross-section that increases the frictional grip of the belt, hence they are named V-belts.

When the pulley's two cones are very far apart (because of the diameter increases), the belt in the groove travels lower, and the size of the belt loop around the pulley becomes smaller. The belt travels higher in the groove when the cones are close together (because of the diameter decreases), and the size of the belt loop going around the pulley is bigger. Hydraulic pressure, centrifugal force, or spring tension can be used by CVTs to generate the force required to adjust the pulley halves. 

Pulleys with varying diameters will always come in pairs. One pulley, called the drive pulley (or variator), is attached to the engine's crankshaft. The driving pulley is often referred to as the input pulley since this is where the engine energy reaches the transmission. The second pulley is called the driven pulley since it is controlled by the first pulley. The driven pulley passes energy to the driveshaft as an output pulley.

If one pulley inflates its radius, the other lessens its radius in order to hold the belt secure. As the two pulleys change their radii relative to each other, they generate an infinite number of gear-ratios from low to high. For example, if the pitch radius is short on the driving pulley and long on the driven pulley, then the driven pulley's speed of rotation decreases, leading to lower "gear." And if the pitch radius is wide on the driving pulley and short on the driven pulley then the driven pulley's rotational speed increases, leading to a higher "gear." Therefore, theoretically, a CVT has lots of "gears" that it can run at any time, at any engine or vehicle speed.

It's good to note that GY6 CVT Transmission kits are interchangeable fitment on a GY6 A-Block or GY6 B-Block, the only thing will vary is the size belt determine by either its a GY6 shortcase engine block or GY6 longcase engine block. If it can fit a 12" tire and above it most likely a GY6 longcase engine block. Thus, 11" tire or below its a GY6 shortcase engine block.

Another way to determine if you have a GY6 shortcase or longcase engine? If it has 10 bolts securing the CVT cover and measures horizontal 17.875" across the CVT cover it a longcase that uses a CVT belt-835-20-30 size belt. If it has 8 bolts securing the CVT cover and measures horizontal 16.142" across the CVT cover its a shortcase that uses a CVT belt 743-20-30 size

For example, the image below shows a measuring tape of a CVT cover, and its CVT gasket could be from a GY6 A-Block engine or GY6 B-Block engine, regarding the CVT belt goes it's from a GY6 longcase 20" engine block. It's longer engine block allows it to fit a 13" tire size which will require a Bando CVT Belt 835x20x30 size.

When replacing your CVT belt you can find similar three sets of numbers imprinted on them i.e. "835-20-30." Taken this example belt size 835-20-30 the "835" means it's 835mm in length, "20" means 20mm in width, and "30" means 30° groove angle.

Here's a complete Super CVT Transmission Kit by Ban Jing:

Ban Jing CVT KIT (GY6)

Description: Ban Jing CVT Kit GY6 aka Super CVT transmission kit for GY6 125/150cc+ engines is one of the best dollar-for-dollar bolt-ons to improve your GY6 scooter transmission performance! Quicker acceleration, reach faster top speeds, and makes your GY6 CVT the smoothest running transmission in town! From rapid downshifting to slow cruising, this thing is smooth. Ultralight balanced components, oversized wear pads, and state of the art polytetrafluoroethylene (PTFE) coatings ensure superior performance and long service life.

It would be recommended that you use a new belt with this kit. You make sure that you keep the belt and the belt drive facing plates dry. For all the other areas, you should first apply a moly-graphite grease when you are assembling. You must re-use stock variator boss, washers, clutch back-ramp plate, clutch nut, and nuts.

Installation: 1. First, slack the belt by opening the CVT clutch on the side of the variator so that it gives the belt slack. 2. Then mount the drive face of the variator when raising the slack belt further away from the center boss will see no splines between the slope-side face of the variator drive and the flat-side boss. And make sure it's flushed together. 3. After that, you should install the existing variator fan, washer, and hand-tight nut. 4. Lastly, just apply blue Loctite, and then torque nut to 30-35ft lbs. For more guidance, please consult your manufacturer variator torque specs.


It includes a Drive face, Roller weights, Variator, Secondary sliding assembly, Springs, Clutch, and Clutch bell.

  • 1x Vented Clutch Bell (12-Spokes)
  • 1x Forged Drive Face Fan: 115mm
  • 1x Compression Spring: 1500RPM
  • 1x Large Shoes Performance Clutch
  • 3x Pillow Springs in Clutch: 1500RPM
  • 6x Roller Weights: 20x12 11gm, 12gm
  • 1x Adjustable Drive Sheave Assembly
  • Made in Taiwan

Supported Models: GY6 152QMI 157QMJ 161QMK 161QML Chinese Scooter, ATV, Genuine Buddy, Kymco, Polaris RZR 170, Ruckus GY6 Swap, Vento

Item Weight & Package Dimensions:

6.581 pounds  | 16.5” (L) x 11.75” (W) x 2.687” (H)

CVT Transmission Kit Installation

DO IT YOURSELF---------------------------

  • Time Required: 60-120mins. 
  • Skill Level: Medium

Chemical Used:

Parts Used: 

Tools Used:

And, there are many more high-quality aftermarket scooter parts available at the NCY STORE. So if your OEM parts fail or get bogged down, let NCY Performance Scooter Parts be your source for finding better and upgraded replacement parts for your GY6 buggy or Scooter.

To check out the latest GY6 CVT Transmission performance parts and accessories, click here.


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