CARBURETTER
A description of the carburetter (Dell 'Orto SHB 18) will serve as a guide to dismantling and reassembling the instrument, which is a straightforward process.
The air cleaner adapter is held to the carburetter air intake by two screws and it has a gasket, seating in a groove. Two screws also retain the top cap which serves as a gasket. The cap carries the cable adjuster, throttle stop screw, lever spring, and throttle slide, the latter being attached to the lever by a hooked rod.
Petrol is fed to a circular cap on the side of the body. The cap is held by a single central screw, has a gasket and contains a flat nylon strainer. The float chamber is held to the underside of the body by two screws, with a gasket in a groove round the upper rim. The float is hinged and the needle seats upwards.
The main jet is central in the base of the body, alongside it is the starter jet. The pilot jet points downwards at an angle into the body, on the right hand side looking from the air intake, and just behind it is a spring loaded screw, running horizontally, which is the pilot jet air screw which regulates slow running.
On the opposite side of the body is the choke valve, spring and cable adjuster. On the engine side, there is a nylon sleeve surrounding the induction stub, on to which the carburetter is clamped by a split ring and screw. On late models, the choke screws down on to a three-cornered shield which covers the overflow hole - this should not be omitted when assembling.
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WHEELS AND BRAKES
Attention to the rear brake is simple and the method of pulling off the rear hub has already been described under "Removal of gears". This can, of course be done with the unit in the frame, and once the hub is off, the brake shoes are accessible. The shoes are held on the pivot by a circlip, once this is removed they can be levered off. When refitting do not forget that a new tab washer will be required for the hub nut, and the latter must be tightened to 65lb with a torque wrench.
The front wheel is more easily removed if a wood block is first chocked beneath it to take the weight. Disconnect the brake cable by undoing the clamping stud and pull the wire free of the clamp - watch for the loose cable stop which will drop off. Disconnect the speedometer drive by unscrewing the sleeve, there is a thin collar inside this which can drop out and be lost.
Undo the spindle nuts until the washers are free of the recesses in the fork links and the wheel will come free - note there is another plain washer on the backplate side, between the inside of the link and the inner spindle nut.
To dismantle the brake, clamp the inner spindle on the drum side in a vice, and undo the nut on the brakeplate side. The brakeplate can now be removed - if difficulty is experienced tap the spindle on the drum side with a hide mallet. With the plate off, the spindle can be driven right out and the two spacers, one each side, levered out. The hub has an oil seal on either side, and two bearings separated by a tubular distance piece. Lever out the oilseals and remove the circlip holding the bearing on the side remote from the brake. The bearings may now be driven out. reassembly of the hub is straightforward, being the above procedure in reverse, but remember to pack hub bearing with a medium grease.
The front brake shoes assembly is similar to the rear brake - again there is a circlip on the pivot, opposite the cam, to retain the shoes.
Before refitting the wheel in the fork, ensure that the spindle protrudes an equal amount on each side. Put on the inner spindle nuts and tighten, then put the thin washer against the inner spindle nut on the brakeplate side. Support the whell on the wood block as it brought up to the forks, and see that the anchorage lug is mated with the lug on the fork link. Put on the outside washers and nuts and tighten.
When refitting the speedometer drive, make sure the thin collar is slid onto the driving cable and then inside the sleeve. Rock the wheel as the cable is inserted into the socket and tighten the sleeve.
When refitting the brake cable, first slip the loose stop on to the cable, then thread the inner wire through the stop-lug. Pass the end of the inner wire between the clamp plates bend it round the screw and back between the tongues on the clamp plates. Note- there is no adjuster on this cable - adjustment is made by pulling the cable end through the clamp with the screw slack. It should not be adjusted so tightly that the shoes are binding when the handlebar lever is "off".
Note when replacing the cable that it should lie above the speedometer cable in the clip on the forks and in the rubber grommet below the steering head. If this is not done, the bend of the cable will be too acute , and it may bind when operated.
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PETROL TANK AND TAP
To remove the tank, drain the petrol from the tank, remove the spit-pin in the tap control rod, and take the tap out of the tank by undoing the large upper nut. There is a felt washer round the tap boss.
Lift out the plastic tool box, and take off the nuts from the two bolts which pass through the two securing tabs at the bottom front of the tank. There is a large falt washer and a shakeproof washer under each nut, and there are rubber grommets in the securing tabs. With the bolts clear, the tank can be lifted out.
Note there is a plastic beading on the flange round the rear of the tank, and a felt washer round the filler cap orifice.
To dismantle the petrol tap, unscrew the large nut at the end of the control rod. This will release a spring plunger, which bears aginst a rubber washer with three holes, inside the tap body. this rubber washer can be replaced if worn. When replacing the plunger make sure the slot in the flat underside is opposite the three holes in the rubber washer. A gauze strainer protrudes up into the tank and can be lifted out for cleaning - when replacing make sure the rubber ring is in position before screwing down the surrounding nut.
Replace the tank by insering it into the frame with the rear end well into the recess. Insert the two bolts through the frame and through the rubber grommets, put on the large flat washers followed by the shakeproof washers and nuts.
When reconnecting the petrol tap control rod, make sure the two parts of the rod are correctly positioned before fitting the split pin. The forward control lever (which protrudes through the frame) should be pointing up when the tap is off.
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AIR CLEANER
This is located below the plastic tool box, in the frame. It is held in position by a spring clip, which when released will allow the filter and it's holder to be lifted out. When replacing note that the filter cover has four tongues which locate it, before the spring clip is put back. Later models have a stud welded to the frame which passes through a hole in the top of the filter cover. A nut is screwed onto the stud to secure.
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CONTROL CABLES
There are six control cables on the machine. The throttle cable has a soldered nipple at each end, whereas the rear brake cable is fixed by pinch bolts at each end. The front brake cable has a soldered nipple at the top (handlebar) end, and is fixed by a pinch bolt on the brake arm.
The remaining three - clutch and two for the gear control - have soldered nipples at the top, and at the gearbox end are fixed by trunnions, which have been mentioned already under "Fitting clutch and gear control cables."
A section through one of the trunnions is shown in the sketch. It will be seen there is a disc within the body, below the nipple screw, and this prevents the screw cutting the wire when tightened. When refitting a trunnion it is most important this disc is correctly positioned.
The cable are housed within the tunnel formed by the pressed steel frame, and replacement of a broken cable can be awkward unless care is taken. Here it may be noted that a broken cable is best replaced by a complete new one, e.g. inner and outer - fitting a new inner wire in an old outer casing does not usually give good results.
To fit a new cable to the handlbar controls involves first removing the handlebar cowling. Remove the headlamp front held by three screws, unclip the bulb holder, disconnect the white earth lead and remove the headlamp front. From under the handlebars, undo the two screws holding the cowling. Push the speedometer cable up a little from underneath the front wing and detach it from the speedometer head.
With the cowling off it will be seen that the throttle and gear control cables are operated by rocking levers on the ends of the twist grip spindles. If one of these cables has broken, it will have dropped down, either out of sight or perhaps still visible.
If it is still visible, see if it can be reached with fine nose pliers. If it can be brought up it can be fixed temporarily with tape or wire, whilst the other end is released. Now attach the new cable to the lower end of the old one with string, and pull gently on the old one at the handlebar end to pull the new one through - it will probably require "feeding" at the lower end as the top is pulled.
If it is not visible, try this method. Detach the lower end of the broken inner wire and pull this out carefully so as to leave the outer casing in position in the frame. Obtain a piece of stiff wire at least twice the length of the cable, bend over one end and slide the new outer onto it. Now pass it from the bottom up through the old outer until it can be gripped at the handlebars. The new outer can now be pulled up into position as the old comes out and finally the new inner fed through from the handlebar end and secured.
There is another method, which may be used when all the cables have to be refitted, say during a complete rebuild of a machine. Get a piece of brazing wire about 3ft long, bend one end and nip it off to make a small hook - this can be screwed left handed into the end of an outer cable. (A little experimentation is required to get the hook into a shape which will hold firmly). Pass this brazing wire through the horizontal tunnel of the frame from the front and pull the outer casings through, until they are underneath the front wing. Now detach the brazing wire, pass it vertically up alongside the steering head until it has emerged at the handlebars, screw on the casings in trun and draw them up - again care is needed, and the casings must be "fed" into position whilst being pulled.
The position of the cables as they come up into the handlebars is important. Of the two gear control cables, the one nearest the rider at the handlebar end is connected to the flywheel side side of the pivoting lever on the gearbox, and the trunnion for this cable is slightly longer than the other. The clutch cable must also come up into the handlebar on the left, and the front brake cable on the right, and when dealing with these cables it is a good idea first to drop the two cowling screws into their bosses, from the top, and make sure the cables lie snugly behind the screws, before the cowling is finally refitted.
The rocking levers mentioned earlier, are fixed to the twist grip spindle by a pin, if this is driven out the assembly can be dismantled. Behind the rocking lever is abevelled washer and an L-shaped spacer which fits over the rod and bears against the handlbar casting. These parts can easily be reassembled in the correct order, but note that the throttle twist grip has a tongued washer and a friction washer, bearing against a boss on the rod, at the rubber grip end.
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HANDLEBAR AND FRONT FORKS
With the front wheel out, remove the handlebar cowling as previously described - first the lamp front, then the bulb holder, earth lead and then the speedometer cable and finally the two screws holding the cowling. Now undo the handlebar clamp bolt, which lies transversely in the hub of the handlebar casting. A 6mm Allen key is required to undo this bolt, which is recessed in the casting. Withdraw the bolt completely - it has a shakeproof washer under it's head.
The handlebars may now be wriggled free of the steering stem, and laid forward on the front edge of the shield.
use spanner 70640 to undo the top ring nut, remove the tongued washer, and use 70641 to undo the upper cone. Support the forks which will tend to drop, remove the ball cage and remove the forks. At the base of the stem is the bottom cone, a ball cage and a rubber protector.
If the fork links are to be removed, proceed as follows. Clamp the forks upside down by the stem in a vice. Put a small box spanner on one arm of the fork-end and pull the link down against the spring - hold - it there whilst the bottom D-shaped rubber buffer is levered out of the box. Release the link, which can now move up appreciably. Insert a square stem screwdriver or bar into the box, with one edge bearing on the bottom of the spring and lever this down until the ball can be removed. Now undo the pivot-bot nut and pull out the pivot. The link can now be drawn out, levering the spring forward at the same time. Finally ths spring and rod can be lifted out - there is a loose coller at the top, against which the spring bears.
On early models the rubber buffers were held by studs with nuts instead of a ball at the lower end of the spring, there was a domed seat in the link on which the centre rod located. Tool 70642 is necessary to compress the spring whilst the domed seat is removed, and this tool is used with the pivot bolt removed first.
Note, that there is a loose inner bush on the pivot bolt, within the bearing in the link.
When re-assembling, first place the spring and the top collar on the central rod, and insert this into the fork leg with the latter horizontal - this prevents the collar dropping off. Now clamp the forks upside down in the vice and insert the link above the spring. the latter must be levered forward until the link will go right back, when the pivot bolt can be inserted. Now the spring must be levered down as before, to allow the ball to be inserted. Once the ball is seated in it's recess in the link, put on the pivot bolt and tighten.
Do not mix up the links - the offside link has a lug which is the brake anchorage.
Slide the rubber protector on ot the steering stem and locate it under the bottom cone. Place the ball cage in the lower steering head race, and pack them with grease. Push the stem into the head, put the ball cage with some grease into the upper head cone, and screw on the upper stem cone. Screw down with 76040 until all play in the bearing has disappeared whilst the stem is free to turn and does not bind. Put on the lock washer, and the top ring nut, tightening this with 70641, holding the top cone with 70640 to prevent loss of adjustment. When the top ring is tight, test the head bearing for excessive slack or tightness.
Refit the handlbar, and insert the clamp bolt tightening with the Allen key. Leave the final tightening until the front wheel has been put back in the forks, so that the handlebars and wheel can be lined up. Finally refit the handlebar cowling, speedometer cable and headlamp front.
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