The really useful magazine - now part of Motor Cycle Monthly

On the Bench: Auto scooter roller change

The inner workings of an auto scooter may seem like witchcraft but they are fairly straightforward machines. This month Haynes show us how to change the rollers on a Vespa GTS. For the uninitiated, the rollers act on centrifugal force. As the revs increase the belt rides up the variator ramp and alters the gearing. Worn rollers (and/or drive belt) can seriously affect the performance of a scooter and changing the rollers for lighter or heavier ones can also be used to fine tune the way an engine behaves, lighter rollers will make the scooter accelerate faster. Scooter tuners often play about with weights and even mix and match them to set up an engine to make the best use of the available power. Although it’s a matter of trial and error, tricky if you don’t happen to have a Dyno! Swapping for new standard rollers is less of a gamble.

The roller weights are housed inside the variator and can be accessed after loosening the air box and removing the drive belt cover. To remove the cover you also need to loosen the rear clutch nut by either using a clutch holding tool (Fig 1) or an air ratchet (they can be bought quite cheaply these days).

To remove the drive pulley nut, the pulley must be locked to prevent it turning. Although Piaggio produce a service tool to hold the pulley, you can hold the pulley around its rim using a rubber rotor strap (Fig 2). If you can’t hold the pulley tight enough you will have to remove the alternator cover and hold the alternator with a socket on the nut to prevent rotation.

With the pulley locked, unscrew the nut and remove the washers, noting their order and which way round they fit (see fig 3,4 & 5). Slide the outer half of the drive pulley off the shaft (see fig 6).

Remove the washer from the end of the shaft, then slip the belt out of the driven pulley and remove it (see fig 7). Note any directional arrows or mark the belt so that it can be installed the same way round. Slide the variator, the centre sleeve and the ramp plate off the crankshaft, taking care not to let the rollers drop out (8 & 9).

Lift out the ramp plate, then remove the rollers, noting which fits where – unless new ones are used, they should be installed in their original locations (fig 10). Also note that each side of the roller is different, with the covered side facing the direction of thrust. Clean all the components.

Check the rollers and the corresponding ramps in the variator housing and ramp plate for damage, wear and flat spots, and replace the rollers, the housing and the plate with new ones if necessary. Measure the diameter of the rollers and renew them as a set if any have worn to less than 19mm (GTS125) or 20mm (GTS250/300).

Check the centre sleeve and its bush in the housing for wear and damage and replace them with new ones if necessary (fig 11).

Check the condition of the guide shoes on the ramp plate and replace them with new ones if they are worn or damaged (fig 12). Also check the splines on the plate and fit a new plate if they are worn.

Make sure the inner surfaces of both pulley halves, the sleeve, the rollers and the ramps are clean and oil-free. Fit the rollers into the housing, making sure they are in their original positions (unless new ones are used), and that the covered side faces the direction of thrust as shown (fig 13). Check that the guide shoes are correctly fitted on the ramp plate, then fit the plate.

Grip the variator so that the ramp plate is held into the housing and insert the sleeve, then slide the variator onto the crankshaft (fig 14). Note: If the ramp plate moves and the rollers are dislodged, disassemble the variator and reposition the rollers correctly.

Position the drive belt around the driven pulley and around the end of the drive shaft (fig 15). Ensure there is sufficient slack in the belt to avoid it being trapped when the outer half of the pulley is installed – if necessary, grasp the driven pulley and pull it towards the clutch to compress the spring and press the drive belt into the pulley to create slack at the front to ease fitting of the drive pulley.

Fit the washer (see fig 7). Slide the outer half of the drive pulley onto the crankshaft (see fig 6).

Fit the thin and thick washers, then fit the nut applying a suitable non-permanent thread locking compound to its threads, and tighten it finger-tight (see illustrations 5, 4 and 3). Make sure the outer pulley half butts against the centre sleeve and is not skewed by the drive belt. Use the method employed on removal to prevent the pulley turning and tighten the nut to the specified torque setting of 75 to 83 Nm (see illustration 16).

Finally ease the drive belt out of the pulley and refit the side casing then tighten the clutch nut.

This procedure was taken from the new Haynes Vespa GTS/GTV/LX/LXV manual which is available now. Visit www.haynes.co.uk for more information.