OZ ATV :: The Australian ATV Forum

[Buzz]

Does anyone have pictures or know how the CVT works? I know it has 2 round disks with a belt running over it and the disk size changes (front & back disk) but does the front disk have a centrifugal clutch inside it? If no clutch, how does the motor engage the belt to make it go around? Has anyone pulled one of these apart and looked inside? If it has a clutch, how long do they last? Which one normally breaks first? the belt or the clutch?

[AussieV]

Ok easy part first. Its very rare for a cvt clutch to break. If it did it would probably blow a hole in your leg. Thats why they are made strong. So the belt , even though they last a hell of a long time if you look after them. I have about 120 hours on mine.

The CVT runs off the crank shaft. It has 2 angled "sheaves" one moves in and out the other stays put. The moveable sheave has a spring and a spider with weights on it to aid the in and out motion of it. When you rev the engine the weights move and the spring pushes to engage the belt. No centrivical clutch.

As the belt engages and you rev the engine more the belt will start to ride up the sheaves at the front (primary) and pull down on the secondry (the back one onto your drive shaft or sprocket if its chain drive). It really is a simple design that is so effective and virtually gives you an unlimited gearing range, hence the name "Constantly Variable Transmission" It varies depending on load and engine speed all by itself so you are always in the so called right gear all the time.

The other thing is you can tune them quite easily to your liking and riding style, with higher stalls, shiftout (where the belt reaches maximum height and has then got to rely on the engine to make more speed) different weights, helixes if you have them in your clutch (polaris) This can be a bit frustrating to nut out, but its very rewarding when you find the right combo for you.


There is a heap more info than this, im just giving you the basics for now.
HTH

Mike
_________________
WORK SUCKS, IM GOING RACING

My webpage and pics

[cowchaser]

Hey Mike thats some good info mate.
_________________
Smitty

[Buzz]

Thanks mike, very well explained, so there really is very little to go wrong with the CVT's and very little or no servicing. Do I need to do any adjusting? I guess not as the sheaves are adjusting them self's anyhow.

So what would happen if I changed the front Chain sprocket to a smaller one Less 1 tooth, and the rear increased by say 2 teeth? would I get more power and less speed like the geared bikes? or would this not make any difference as the belt automaticly adjust's anyhow??

Other question is? if the load for the quad is too much will the belt start slipping? or the CVT will disengage? obviously the engine wouldn't stall!

What will happen if the rear wheels are spinning in the mud and then the quad hits some dry hard surface which will make the rear wheel grab in a hurry, will the belt than possibly snap!

Sorry, lots of questions, just supriced that this CVT system is so good and why are all the big boys not using them on the quad bikes?

Hornet

[AussieV]

Gearing on the bike if you dropped sizes or added extra teeth will sill have the same effect on gearing. But if you decide for taller gearing the CVT will lower itself to pull the tall gearing easier, so it finds its own happy medium due to the load.

Loads on the bike can damage a belt. Generally if they slip they just glaze the sides of it so it wont grip on the sheaves properly. Can be fixed with sand paper sometimes. And yes sometimes they do blow belts but not too often. It takes a lot of load to stuff a belt.

With the mud onto hardpack spinning the wheels there is no problem. If the rears grip all of the sudden the rear clutch which is torque sensing so to speak will drive the belt upwards so it drops the belt on the primary. What this does is drops the speed of the wheels and stops any belt slippage from happening.


Now with the pros not using them. Main thing is weight. They can be heavy. So thats probably one reason. Other reasons , I dont know.

A well set up CVT bike should, in general, always get the holeshot on someone with a standard gearbox. Again this is all due to getting the power to the ground more efficiently and being in gradual gear changes all the time.

Mike
_________________
WORK SUCKS, IM GOING RACING

My webpage and pics

[Buzz]

Thanks, Mike you obviously have pulled some of these down and know how they work, not many people understand them and thus thye always will argue that gears are better then CVT - Thanks for the info now I feel a lot more confident.
So, increasing the rear sprocket with more teeth will not realy give me a lot more power to do any burn-outs

Good to know some peolpe on this forum do know something abt the technical side, rather then just talking about jumping 10m in the air and killing them selves and doing a 150Km/h

Thanks Mike

[AussieV]

No Problem

You will still be able to do burn outs no problem. I do em on concrete sometimes. Also pushed and pulled some real heavy loads. I have push started sprintcars on concrete too with no belt slippage or adverse affects. So thats how much punishment they take.

On the CVT Im still learning. Getting there. But I also know that if you can set it up for your riding style and HP etc, you gain more ponies because its not robbing much from the crank. Increases of 5% or more is not uncommon.

Mike
_________________
WORK SUCKS, IM GOING RACING

My webpage and pics