Changing the drive belt on a scooter.

[Uncle Flash]

A scooter drives the rear wheel with a V belt that looks remarkably like a fan belt. In fact, Gates make a range of belts that will fit some scooters so it’s worth having a look for a less pricey option. Most automatic twist and go scooters use this method and whilst a 180cc is shown here, nearly all auto scooters will resemble this layout. As the drive belt wears, it becomes thinner and the belt sits deeper in the pulleys causing a loss of top speed and slower acceleration. The specifications for each scooter can be easily found on the ‘net.

First job to do is remove the side cover to reveal the belt. To do this, you may have to remove the airbox that houses the air filter, which is normally attached to the top. The kick-start lever and any other attachments can be left in place while the cover is removed. You will be left with something that looks like this:

The front pulley and the mechanism behind are called the variator. The faster it spins, the narrower the pulley becomes moving the belt toward the outer edge. This pulls the belt deeper into the rear pulley, which is normally compressed by a large spring behind. The mechanism on the outside of the rear pulley is the clutch, which engages at a preset rpm. The front and rear pulleys are held by one large nut each.

To remove these nuts you will need to lock each pulley. The front is locked in place using a special tool. It is possible to do this job without it but considering the small outlay and the ease of which the job becomes, it’s worth borrowing/stealing/buying your own. The tool I used is made for 50cc models but I was able to make it fit mine with a small modification that shows just how similar all scooters are.

Remove only the outside of the front pulley being careful not to lose any washers that will be present. The belt can then be removed from the front and pulled from the rear pulley. Sometimes (as here) the space between the rear pulley and the transmission housing will require that the rear pulley is removed complete with the clutch. The rear nut can be removed if the clutch is held by pin pliers but I used a strap wrench. Once the nut is off, the complete unit should slide off the shaft. Do not disassemble the clutch as it can spring apart and be painful to put back together without special tools. Remove the old belt from the rear pulley leaving this:

When the old belt was removed, the rear pulley will have closed up. With 50cc models this is not a huge problem. Just place the new belt around the pulley and pull it into the gap by pushing the pulley with your foot. Some rear pulley springs are so weak they can be compressed by squeezing them with both hands but it can then be awkward to fit the belt. With larger capacity scooters, the spring will be stronger but bear with it. The side that moves is the one closest to the clutch and it rotates slightly (clockwise from memory) as it does.

You will need to do this to ensure the belt fits far enough over the front pulley for it to be assembled. If there still isn’t enough slack but it fits over the front shaft, assemble the pulley to hold the belt while you squeeze it near the clutch. This should pull it further into the pulley giving you enough slack to assemble the front pulley.

The belt must be fitted with the arrows pointing in the direction the belt moves. Every one I have seen so far is clockwise. Remember to tighten the variator and clutch nuts to the correct torque and that most manufacturers require that these nuts be renewed during this operation. Replace the cover and tighten to specs again. It might not look like it but the cover is normally a structural part of the transmission and adds strength.

If anyone needs to borrow my variator locking tool, shoot me a pm.

[deeman111]

Wow. I always thought that scooters were like mobile phones. When it needs fixing you throw it away and buy a new one!

Good write up, nice to see how the little buggers work.

James

[Xuaxace]

This is no ordinary scooter mate

[Uncle Flash]

I believe there are only about half a dozen distinct types of transmission in use and like half the 50cc world uses the same design and that includes the Chinese variants. And with the covers off they look just like my 180cc.

A good example for WA would be the 50cc Monza. The engine is a copy of a common European/Japanese design also used in Yamahas etc.