Variator Setup, Modding, And More

[90GTVert]

I'm going to start out with the most basic variator setup info and parts identification. If you don't know what the parts are, it's going to be hard to understand how to set them up.

Shown here is a typical variator setup for a Yamaha Jog / Minarelli / 1E40QMB two-stroke engine. Other engine types may use slightly different configurations, but a lot of the info here can apply to other platforms.

From left to right (numbered to correspond with images below) : Variator Nut (#1), Washer (#2), Kick Starter Pawl (#3), Variator Woodruff Key (#4), Variator Fixed Plate (#5), Variator Moveable Face (#6), Variator Drive Boss (#7), Variator Ramp Plate And Guides (#8)



#1 : Variator Nut : This is generally a half nut (half the depth/threads of a standard nut). Shown here is a whole nut (all I had lying around without disassembling something). Simply holds the vairator components in place on the crankshaft.



#2 : Washer : A washer that fits between the variator nut and the starter pawl.



#3 : Kick Starter Pawl : This allows the kick starter to lock in place when the kick starter is used.



#4 : Variator Woodruff Key : Sometimes called a star washer. This specialty washer fits into a reciever groove in the variator fixed plate (#5) and onto the splines of the crankshaft to lock the fixed plate into position on the crankshaft.



#5 : Variator Fixed Plate : Sometimes called the Variator Fan or Fixed Sheave. This is one of the two drive faces that the belt rides on inside of the variator. As it's name implies, it does not move... or rather it rotates fixed to the crankshaft, but it's position does not change otherwise. The blades on the outside of the plate aid air circulation inside the CVT.



#6 : Variator Moveable Plate : Sometimes called the Moveable Sheave, or simply the Variator. This is where the action is. This is the other half of the faces that the drive belt rides on. This plate moves in and out, controlled by the forces of roller weights driven by centrifugal force, to make the belt ride higher or lower between both variator faces.





#7 : Variator Drive Boss : Sometimes called the Sleeve. This spaces the variator plates, or more accurately it separates the variator ramp plate and teh fixed plate. The moveable face rides on the drive boss.



#8 : Variator Ramp Plate and Guides : The Guides (black plastic pieces) are sometimes called Slides or Bushings. The ramp plate rides on tracks in the variator and it positively located on the crankshaft's splines.



Roller Weights : Roller weights ride in tracks inside the moveable plate of the variator and help to open and close the front pulley.

[90GTVert]

Now that you know what the parts of the front pulley are, let's take a look at exactly how they install on the crankshaft. I'm using an old uninstalled crankshaft for demonstration purposes. You should be looking at something like this (plus an engine lol)...



The first thing to go on the crankshaft's splines is the ramp plate, and then the drive boss.



The the moveable face will go into place over the ramp plate and drive boss. I actually find it much simpler to install the rollers in the moveable face (2nd pic below), then slide the ramp plate on (3rd pic below), and then instert the drive boss and slide the whole assembly onto the crankshaft at once.







Then the fixed plate slides on.



The woodruff key locks into place on the splines and the fixed plate.



Then the kick starter pawl.



Finally, the washer and nut go on.





Here's a view of the whole assembly installed. This is a typical stock setup for a Minarelli/Jog engine.

[90GTVert]

We need to understand basically what the variator does to undestrand what we'll be trying to accomplish with variator setup, tuning, and modding.

The CVT is essentially made up of two pulleys, a belt, and a clutch. The front pulley (variator) is driven by the engine's crankshaft. A belt connects the front and rear pulley. Once the rear pulley spins fast enough, the clutch will engage and turn gears inside a final drive transmission (fixed ratio) and ultimately turn the rear wheel. The image below shows a typical CVT setup on a Minarelli/Jog style engine.



There is a spring between the clutch and one side of the rear pulley called a contra spring or torque spring. That spring holds the rear pulley closed, which keeps the belt on the outer edge of the rear pulley at rest. Since the belt is on the outer edges of the rear pulley, it should be sitting near the center in the front pulley that is open at rest.



As engine RPM increases, the roller or slider weights inside the variator are pushed outward along their tracks inside the variator. This movement and force causes the front pulley to try to close and push the belt toward the variator's outer edge. In order for the front pulley to begin to close, it must act against the force of the contra spring trying to hold the rear pulley closed. This is where CVT tuning with proper weights and springs comes into play. The weights must be heavy enough to overcome the force of the contra spring. If the roller or slider weights are too light or the contra spring is too stiff, the front pulley will not be able to close all the way and push the belt outward in the front pulley and adversely inward in the rear pulley. If the weights are too heavy or the spring is not stiff enough, the front pulley will close very fast (at low engine RPM) and push the belt outward in the front pulley and to the inside of the rear pulley prematurely. The trick for getting the best performance is to find the right weight and spring stiffness to allow the CVT to operate at an RPM range within your engine's peak output. The image below shows the belt's position at higher RPMs when tuned properly.



This video shows a GY6 50cc and a Minarelli CVT in action.



The movement of the belt form it's position at rest to it's high RPM position is like changing gears. At rest, the belt sits low in the front pulley and high in the rear pulley. The front pulley is acting as a small pulley, and the rear pulley is acting as a large pulley. The small front pulley has to rotate multiple times to rotate the rear pulley once. This puts the engine under less load to move the rear pulley and ultimately the rear tire, but if the "gearing" stayed this way the engine would be revving to it's peak at low speeds.

In order to keep engine RPM at the appropriate level and achieve high speeds, we need to change "gears". The motion of the belt toward the outside of the front pulley and inside of the rear pulley does just that. Once the belt reaches the outside of the front pulley and the inside of the rear pulley, it should take less than one revolution of the front pulley to roatat the rear pulley once. That puts a lot more load on the engine, but allows the rear pulley to turn very fast and in turn rotate the rear tire fast enough to achieve higher speeds.

The beauty of the CVT isn't that it has a high and low ratio as described above. The really great thing about a CVT is that it has a seemingly infinite number of possible gear ratios between those two points. A standard transmission on most motorcylces has 5 or 6 gears that the rider selects. That means that during acceleration engine RPM rises, then the rider shifts to the next gear and RPM drops and then rises again as it accelerates, and this continues throughout every gear. CVT transmissions do a much better job of keeping the engine at it's peak power level by changing through lots of progressive gear ratios from start to finish rather than just a few. This is why it is extremely important to get the CVT tuned properly to stay at the peak power RPM when accelerating if you wish to have maximum performance.