THE CLUTCH

Dismantling.

If the gearbox has not been removed with the engine from the frame the preliminary work of taking off the dynamo belt cover, belt and primary chain, etc. (see page 31) must be carried out. Unless attention is needed to the sleeve gear ballrace the inner half of the chain case can be left at-tached to the gearbox.

Draw the clutch assembly off the sleeve gear and push out the three thrust pins from the back plate. With the clutch assembly resting on the back plate lift off the component parts one by one beginning with the front plate. The ballrace is a sliding fit on the centre of the back plate and tight in the chainwheel.

One clutch plate with inserts, and one steel spacing plate fit between the front plate and the chainwheel. Between the chainwheel and the back plate there are two clutch plates and two spacing plates fitted alternately-steel to friction lining. The inserts will continue to work satisfactorily until worn flush with the metal surrounding them. They must be firm in the plates and chainwheel. The ballrace must be quite free.

Relining the Clutch.

Worn inserts can be pushed out of place and renewed if necessary. Press in new inserts leaving them projecting an equal distance each side and make certain that the working surfaces are all level. Pressing them up against a truly flat surface will ensure this.

Reassembling the Clutch.

The back plate must be held firmly from rotating during re-assembly otherwise the spacing plates cannot be engaged with the front plate. The best thing to hold the plate is a disused sleeve gear from any single cylinder model Velocette. This is gripped in the vice by the gear teeth or driving dogs, and the clutch back plate fitted loosely over the splines.

Fit the first clutch plate in position followed by a spacing plate, second clutch plate, and the second spacing plate. Note that the external tongues on the clutch plates and internal tongues on the spacing plates must all point away from the chainwheel, i.e., downwards.

Centralize the four plates with the back plate, bring the tongues on each pair of plates into line and engage the internal tongues of the spacing plates in the slots machined in the back plate just inside the ground friction surface.

Hold the chainwheel with the deeper slotted rim underneath and fit it into position with the ballrace over the boss of the back plate. Enter the tongues of the clutch plates in the chainwheel and see that all friction surfaces come into contact. With the chainwheel fitted, put on the third spacing plate and clutch plate in that order and with their tongues pointing upwards, those of the clutch plate being engaged in the slots in the rim of the chainwheel. Centre the spacing plate carefully as its internal tongues must engage in slots on the clutch front plate.

Fit the front plate over the tongues of the back plate and move the chain-wheel backwards and forwards maintaining light pressure on the front plate until it is felt to go into place and lie flat on the friction linings as the tongues on the spacing plate enter the slots.

See that the spring holder is screwed into place in the front plate, and fit the three thrust pins into the holes in the back plate sticking them in with a little grease.

The clutch assembly is now ready for refitting.

The Clutch Thrust Bearing.

This is a ball thrust bearing seated spherically in the clutch thrust cup and located centrally upon the sleeve gear by a distance-piece pushed over the sleeve gear behind the clutch back plate. There are three parts to the bearing ; a hardened steel thrust ring flat on both sides, a cage carrying the bearing balls, and a spherical thrust washer. This has a spherical face to fit the thrust cup and a flat face providing a bearing for the balls during the operation of the clutch. (Fig. 10).
The thrust bearing should be inspected for wear. If pitted the parts affected should be replaced. The plain thrust ring if pitted on one side only often can be reversed to give it a new lease of life. Inspect the distance piece for grooving due to wear and replace if worn. If a new caged ballrace is fitted see that there are no rough edges on the cage that would prevent it sliding freely on the distance-piece. Coat all parts with grease before refitting.

The clutch thrust bearing is not intended to carry a constant thrust load, and when the clutch is correctly adjusted is loaded only when the clutch lever is operated, and the clutch is disengaged. It is therefore important at all times to keep the adjustment correct and when driving to avoid keep¬ing the machine standing in gear with the engine running for longer than is necessary. In circumstances where the engine cannot be stopped, i.e., in traffic blocks, always select neutral.