Inside the CVT - Belt and Rollers

of rollers and belts



2010-10-16
36000 Km / 22500 miles with the same belt and rollers in a Piaggio MASTER 500 cc engine

What did I learn from that?

First, the changing intervals are for worse case scenarios like you are in a very cold area and the belt gets frozen stiff and then rapidly flexed during warm up, or when the air is very dusty and the sand in it wears down the rollers fast.

Now my test was done 280 km west of the Sahara and because of the SAL, Calima and Scirocco we get lots of fine sand dust and sand here so for even this kind of extreme grinding air we have here, the rollers would have been good for at least 40.000 km.

If you take a look at your rollers and you see a little abrasion or tiny flat spots like this here.





at 36000 km (if you zoom in you can see very well the different wear patterns)

or this on at 18000 km

let´s take a closer look at our worse case scenario here.

Our patient is 18000 km old and has a big bald spot.
Did this effect in any way the function or safety of the whole cvt?
NO!
So why do some rollers have these spots and others not?
In the optimal case the groove in the pulley is smooth and clean, so our roller can actually roll a bit once in a while and uses the whole circumference. 
But if not everything is optimal our roller who is pressed with some force between 2 metal parts (the pulley halves) moves them apart via centrifugal force by just sliding. So the plastic from the roller always rubs on the same spot where it will loose some material over time.

Does this roller needs to be replaced? If money is not important, sure. But if you just rotate the roller 90 degrees it is good for a long time to do its job.

How do I know?
because this roller spend some time in the 4 roller Colt conversion setup and there the rollers have to do double work load and the bald spot did not progress.

So how do I know when my rollers need to be replaced?
That is easy, a normal roller from the MASTER 500 cc engine has a diameter from 25 mm and as long there is no change the roller is fine.

So do I need to take the rollers out and measure them every xxx km?
No, your cvt will let you know when it is time to change them by not being able to do V-max any more.

The V-max from the Piaggio MASTER 500 cc engine is around real 160 km/h at 8000 rpm. This is when the limiter kicks in and tells you that the engine does not want to rotate any faster.
In my case the V-max was reached at 140 something km/h.

How did my rollers look? Take a look at the first picture and you see they do not look different in the pulley than in the picture below where they had been used only half the km than in the first picture.

So I took one out and measured

This 3 mm we lost were enough to drop the V-max by 8%

Conclusion:
The plastic part of the rollers where I knocked the sides out to experiment with different weights were good for another 16000 km after already giving me 18000km of dependable service.

So if you leave your 8 rollers in, then normally 40000 km + is a piece of cake for them.

I will do a long time test to see how long the 4 rollers last in the Colt conversion.

Here are my rollers from the Piaggio MASTER engine 500 cc after 37000 km
The knocked out sides (good to see at the most left roller) happened when I wanted to remove the steel insert for weight changing.

The wear I had as shown on the 18000 km pictures did not increase since I slightly rotated them at reassembly. But since the plastic with the knocked out sides lost integrity it started to deform. That did in no way affected the performance of the rollers.

Now the part what can give you grief in the cvt is the belt.

This is how it looks like new

The belt has a new width from 26.2 mm and a replace width from 25 mm.
Well, I measure more 26.4 mm

after 18000 km there is some loss of thread between the upper and lower layer and we have the first little cracks in the teeth area

after 18000 km there is also some major abrasion on the top where the belt rubbed against the transmission case. The belt did not loose to much in width, looks like 3 mm compared to the new one.

The same belt with 34000 km, now on nearly every tooth are little cracks but when you think about how much a belt gets bend and unbend every minute the engine is running that is some sturdy material.

closeup at 37000 km

Same belt 3700 km the fissure is 4 mm deep. I decided to replace the belt and keep this one for emergencies since there is still some wear in it.

So will the teeth break off then?
No, the main two ways a belt can fail is separation when the top part gets ripped of the bottom part due to fatigue or excess scraping on the transmission case.


When you look at the transmission case you see on the bottom where the belt had contact because of flapping. Flapping weakens the connection between the upper and lower part of the belt. On the right you see where the majority of the scraping took place.
For more pictures see: Piaggio Master 500 cc - Washer and Dryer performance mod Test

If separation happens you might notice that instantly in higher rpm and lower speed and maybe a mechanical noise.
If you can stop instantly you have a good chance that no damage is done.
If you are lucky you might be able to limp slowly home.

In case you are not so lucky this might await you.


The other way a belt can fail is by braking.
An easy way to check is twist the inside from the belt to the outside, bend it a bit and check for beginning cracks.like this.



bend even more at 37000 km.

This is still OK and no reason to worry, but if you mark it (like I did here with spray paint) then it is easy to check all few thousand km that particular part of the belt by just removing the silver cover from the transmission and look into the vent openings to see how your belt is doing.

What you see above is that one side of my belt at 36000 km has not lost a bit of the anti stretch thread


So here are both sides of my belt at 36000 km. (click on the pictures for full size)

I should have have been on belt no. 4 by now at 36500 km (12000 km changing interval) but I think my belt is good for some more. I am aiming for 50000 km.