Gear trains and selectors

As previously described, the gear trains and the selectors are now out of the lower crankcase half. Before you dismantle further, very carefully look at the accompanying drawings. These drawings will explain exactly what goes on inside.

The gear trains have remained pretty much the same over the years although there have been a few gear size changes. Other major changes amount to the following: Early 1000s used the 750 trains until frame number 3707, in late 1975. From then on a needle bearing was used instead of a bronze bush for 1st gear on the layshaft. This also meant a change in ¡ayshaft so that two circlips and three shims could be used on that end of the shaft to locate that bearing properly. At the same time the 1st gear was changed (shortened to provide easier riding) as was its integral primary shaft, of course.

The SFC, at least late ones, had further small changes too, apart from certain gear sizes. For example, 5th gear on the primary shaft runs on three needle roller bearings perhaps to ensure long life for gearbox sprocket support. A close ratio mainshaft is also offered on the Triple. Although the mainshaft differs, its 5th gear and needle bearings are those of the SFC.

Dismantle each shaft separately and do not muddle bits up. A pair of circlip pliers will be necessary for the circlips on each shaft. All the bearings should pull off either using your hands or with a suitable sprocket puller. There is nothing complicated whatsoever in dismantling the gear trains, the gear shafts operate without end float. With each shaft apart, clean all the components and then inspect them.

The gear teeth, dogs and their cutouts should be free from chips and scores and obviously they should have been easy to remove from their shaft. Check the splines too. Both the primary and layshafts should be straight. No gears or shaft should be blue from excessive heat. The faces of each gear should be clean and unworn. The ball bearings of the primary shaft and the roller of the layshaft should be checked in the normal manner. Look again at the diagram and note the sequence of gears, their bushes and bearings and then circlips.

Before assembling, oil all the bearings and their mating surfaces. The only real point to watch is that the flat face of the 'lock collar' or selector ring should face the 5th gear's dogs on the primary shaft. The other side is slightly recessed. Before finally refitting the gear trains to the crankcase make sure that you have all the half rings in the right places. Do a dummy run first. Den t forget to fit the selector drum first!

To remove the gear selectors first pull out the pin which locates the selector fork shaft into the : - ank case. Then screw in a suitable setscrew to the same end of the selector fork shaft and pull the ;a:: through with it. Make sure you have noted how the selector forks lie before you remove them.

To remove the selector drum you have to undo the nut on the drum's shaft just inside the a b nrtfc»m

1 All the gear trains and selectors with the clutch on the right and the gearbox on the left

Watch the state of these facing dogs - they should lot be worn or chipped for easy shifting and constant engagement

The selector ring should face the 5th gear's dogs on the primary shaft as shown

Selector fork shaft holding pin in the crankcase

Note the set screw which is located in the end of the shaft to enable the shaft to be extracted

A slim open ended spanner is the one to use here

That is the brass coloured screw - it's a bearing retaining screw

The gear clusters - there are minor differences between early Twin, late SF3, SFC and early and late Triples but they are not significant to the dismantling, only to part ordering

crankcase. See the photograph. Once loosened and off its thread pull out the drum shaft from the other end and try to catch the washers and spacers. The complete drum should then be free to come out of the crankcase. All that will then be left will be the 'ratchet* mechanism for the selector drum. This is easily removed by undoing its pivot set screw and unhooking its spring (tension).

There is one more screw which should still be in the crankcase half. It's brass in colouring — it is a bearing retaining screw. A stopscrew almost. Before reassembling the selector drum and selector forks into the crankcase you must check all the components. The drum must not be worn, the ratchet's tension spring must be strong and the forks themselves should not be shiny and unduly worn, and they should be straight. The only basic difference between the Twin and Triple in this area is the mechanism used on the SFC. That difference is one of lightness — the SFC's selector drum is drilled.

Check the selector drum complete in the crankcase lower half. Insert the key in the drum shaft and pass the shaft through from the outside into the selector drum — placing the notched washer between the inside of the crankcase and the drum and engaging the key with its slot. Thread the plain washer and nut over the end of the drum shaft and then tighten the nut with an open ended spanner to locate the selector on its shaft. Replace the roller lever and its spring. Now holding the selector on its shaft, replace the roller lever and its spring. Now holding the selector forks in their positions, insert the spindle and lock it in place with the locating pin. The selector forks should be fitted as follows: wide fork with boss to right hand side, narrow fork with boss to right hand side and narrow fork with boss to left hand side.

Check the full operation of the complete mechanism. Oil all the components. You can now fit the two gear trains in place.

NOTE: The selector drum is a two part affair. It is located, top to centre by a peg and two straps and four setscrews.

The neutral light switch sits in the lower crankcase half and is activated by the selector drum. It makes good sense to remove it before working on the selectors. It cannot be repaired, only renewed, if it is faulty. Make sure its washer is fitted for it is a common point for oil leakage. 0.5 and 1.0mm aluminium washers are available to shim the switch it it goes too deep into the crankcase and provides a 'constantly on' light, even when in gear.

0 0

Post a comment