The front pulley is an automatic centrifugal clutch that drives the rear pulley via the belt. The front pulley is similar in design to other centrifugal clutch systems, in that it has a numbers of weights placed between two plates which when rotating push the plates apart and thus engage the clutch.
I have taken some pictures of the reassembly of my front pulley to show what goes where as it is a complicated layering of parts that make up the clutch.
1. onto the bare spindle goes a small spring, the cog (shown) and, importantly, two semi-circular retaining wedges. Be very careful not to lose these wedges!!!!
2. Next goes the back plate and two washers as shown
3. Then the bearing
4. Followed by this central thingy-me-bob (yes, that is the technical name)
5. Over the top of this goes the clutch back plate and with the weights placed
6. The front clutch place goes over this and the weights should all nestle into the clutch housing neatly. This is all held in place with a screw over the centre spindle.
Not shown here, but there should be 3 push springs slipped over the 3 protruding poles that will eventually hold your cotter pin.
7. Then the clutch cover (in this case i have sprayed mine a rather fetching shade of red) and fit 3 new cotter pins as shown.
Pushing the cover over the springs and placing the cotter pins is quite fiddly.