Throttle cable and twistgrip- removal dismantling and renovation. Clutch cable removal-refit

My apologies for spending ages and loads of pics explaining the bleeding obvious but this took longer than Id expected  and revealed a more complex twistgrip function than I had expected. In brief- having shown that the bike would run I'd found the throttle incredibly stiff and thus needed sorting. I'd suspected it simply needed greasing, but to do this properly I really needed to remove and check the whole length of the cable. Removing the carburettor end was easy (covered before) and all looked fine there so I moved on to remove the twistgrip end. To do this you have to remove and dismantle the twistgrip- and to do that you need sufficient slack in the cables to pull it off the handlebars. The throttle cable was now free but the front brake required disconnection. Slacken the cable at the wheel adjuster- mine was rusted and jammed,  and pushing the brake lever on the wheel against the spring allowed me to fiddle the nipple out from its yoke; seemed a complex nipple at the this point with a brass cylindrical section bonded to the nipple proper.

Compressing the lever allowed the cable to slip free

Cleaning the end showed that the brass section was in fact free and seems to be an end plug to the covering hose-in my case split and beyond use.

Disconnected the lever end and then removed the twistgrip- its held by a single large screw- shown here after grip removal. 

This is here just to show my dismay that the bars were so corroded- they had once been so nice and remained so under the twistgrip.

The released grip was now hanging from the throttle cable

It was easier to examine now and to my surprise it contained two grub screws. I'd expected one- the larger one shown below with its head pointing at the camera as part of the grip rotational friction control- but the second was a surprise. This was screwed in from the other direction but its base had been peened over to prevent its removal and this is visible on left of the grip.

Turning the grip over revealed the head of this second grub screw.

Inside the grip the throttle cable entered a complex 2-block system- it passed right through the upper block via a groove and this could be removed by simply slipping it up the cable inner...

... and pulled back to detach.

This block has a groove or notch on the back

Looking inside the grip shows that the second grub screw is partially exposed and this seems to fit into the notch or groove on the rear of the upper block. I presume this was a modification to hold the upper block in place but I'm surprised it wasn't simply molded into the casting- too tricky or perhaps too soft wearing?

Pushing the cable inwards allowed the lower (termination) block and cable to pop out of the grip. It was necessary to rotate the twistgrip fully to allow the block to come free and the reason for this became obvious once the block was extracted and cleaned.

The cable nipple sits in a hollow in the termination block.

 the other side has a diagonal protrusion

This fits into the spiral groove contained in the rotating section of the grip. This means that as the grip is turned the termination block (and thus the cable end) is pulled further downwards inside the housing- its a straight pulling action unlike say the Quickly where the cable is progressively wound around a rotating sleeve. In theory this should result in less wear on the cable but sadly in my case that wasn't so (see on). The grip needs to be fully rotated to release the cable termination block.

Examination of the cable shows that the Bowden is hopelessly frayed accounting for the stiff rotation- there is no way this can be reused. I think I'll need to get a new one made up because there are no UK suppliers and my soldering skills wont allow me securely to attach such a small nipple.

Looking inside the newly empty twistgrip you can see the rotating inner sleeve with its spiral groove. In my case this wasn't too bad but it was rusty and notchy in operation. You can also see the line of the second grub screw in the back of the groove. I'd really like further to dismantle this and clean it properly,  but how to do so was initially a mystery

I didn't think that removal of that grub screw would really help but I did want to clean everything. Since the head of the screw was accessible I decided to remove it.

I used some small, snipe-nose pliers to undo the peening of the far side and the screw could then emerge fully.

I couldn't at first see how to separate the two halves of the twist grip - stock and rotating sleeve, although there is a clear latching section against the grip (finger indicates below).

Its a bit clearer after cleaning.

Mystery solved by levering the grip flange backwards. This revealed another small grub screw hidden beneath.

I used a wide flat cycle spanner to tap the grip back so I could get a screwdriver onto that grub screw.

The screw was a little tight but it did loosen...

...and as it did so the cover ring with its latching section became loose. With the screw out the cover ring could be rotated clear of the retaining lug and lifted away leaving the sleeve in position.

The sleeve then just lifted out. In my case lack of grease has allowed part of the sleeve to rust and this probably accounts for the crunchy throttle action

Looking back inside the now empty stock shows the friction plate with its grub screw also peened into position. Its going to be impossible to un-peen and re-peen this screw given its recessed position inside the stock so I left it in position and cleaned the grit out from under it with carburettor cleaner spray.

I then cleaned all the components and sprayed them in WD40 for storage as I can't reassemble until I receive the new throttle cable which I have ordered from Venhill of Dorking. They will make it by copying my old cable as a template. In the meantime I removed the brake cable completely and used heat shrink tubing to cover any splits before lubricating it thoroughly. Luckily that cable can be salvaged.

I then turned attention to the clutch control, loosen the cable adjuster- again rusty and siezed.

Release the clutch arm end- don't lose the spring.

Withdraw the cable taking care not to loose the collet that terminates the cable before the clutch arm housing. Its visible here  just outside the case.

Make a note of the cable routing.

Then release the cable from the lever end, remove the lever and cable termination. Then tap the grip off the bars as before using the flat spanner, loosen the screw holding the lever mount.

And pull the mount off the bars for cleaning. I cleaned all the components and re-lubricated the clutch cable prior to reassembly.

 

Bars and switches

Having removed both twistgrips and the nacelle the poor state of the bars and the dodgy connections to the switches became evident. I decided to remove these components and the bars themselves in order to derust them, before deciding whether to rechrome anything.

Handlebar switches- note new and non-standard push button switch on rhs (now disconnected) and original Horn/Dip/Kill switch combo on the lhs. Mirror fitted on rhs is also corroded.

The bar-mounted rear-view mirror was badly corroded although the glass serviceable. I decided to remove and de-rust in case it can be salvaged. The horn button next to it is a later addition- originally the horn would have been integrated into the dip switch control, but this was broken on this bike and a PO had wired in this separate pushbutton switch- although this was also disconnected by now! Removal of all these items was quite straight forward.

New push-button switch

The bars are held on by 2 bolts passing through a fishplate (shakeproof washers above). The fishpklate incorporates hex angled cut outs which should fit over the steering stem nut to lock it in place and prevent it unscrewing- in my case these are not correctly fitted.These bolts screw into captive threads below the brackets which are part of a bar-mounting plate.

Bar mounting nuts, shake-proof washers and fishplate

Loosening the bar mounting nuts releases the fishplate- note that the hex cutouts are not locking the steering stem nut/
.

Viewed from the side it can be seen that the bar clamps are different sizes and the smaller side goes above the bars. The bar-fastening nuts screw into the handlebar mounting plate

Side view of handlebar fastening- bolts fix into handlebar mounting plate

The bar mounting plate is fixed on the forks  by two more bolts. This does allow some angular adjustment and also incorporates an earth lead connection from the headlamp holder.

I unscrewed the two mounting bolts and removed the bars.

The horn/dip switch was removed by removing the bar clamping screws although I will need to replace this with an integrated dip/horn unit and restoring the wiring to its correct route. 

I cleaned all small parts in the sonicator and then put all (inc the handlebars and foot shafts) to derust in citric acid. After a few days these were rinsed thoroughly and treated with Kurust. This was allowed to react and unreacted kurust washed off with methylated spirit. At this point I decided not to re-chrome for the present but sprayed in silver Hammerite.

I then tackled the wiring which appears to have been modified to use an NSU Quickly lighting control- several wires have been re-routed and some replaced with non standard colours...so even  without the few that were already clearly damaged, broken or disconnected it was going to take a while.

I started with the handle bar mounting bracket earthing wire- now brown and too thin. This earths via an uninsulated m8 eyelet onto the bar mounting plate. 

Handlebar mounting bracket earthing point- thin wire and corroded contact eyeley.

This wire was too thin for the expected current so I  decided to replace it with a thicker flex. Removing it was however a challenge; the 12mm nut on the exterior was easy but the 14mm on the inside was inaccessible. I was forced to jam it with the wedge section of a screwdriver in order to loosen the outer nut. 

Removing the handlebar mounting bracket nuts by jamming the internal nut

I could then remove, clean and replace the contacts and wire, treating them to a light smear of dielectric grease.

Moving on to the "kill" wire function- The black "kill" wire (presumably from the lt induction coil) was broken and largely missing. If I'm going to reinstate this function I clearly need a new wire. This originates behind the stator so I marked stator position with punch marks to restore timing before removing it. 

Punch mark

Punched marks to register timing position

I found even then the connection to the coil was inaccessible, and rather than disturb the coil position by removing it, I simply introduced a new length of black wire with a modern crimp connection hidden behind the stator and reused the original bullet connector to the loom.

Kill wire connected behind stator

 

Finally I restored the black HT plug into the crankcase opening and refitted the boot which finished my attention in the magneto area.

The kill function would normally be handled by the multifunctional light switch- which in my case is missing. The kill function has been taken over by a separate kill button. I need also to replace the Horn/dip switch. Thinking about it a neater solution would be to fit a Wipac Tricorn switch handling all three functions- and eventually I may do so. 

Horn dip and kill

On this bike the kill switch had been moved to a handlebar button when the lighting switch was replaced because the new switch was too simple to support that function. 

The combination Horn/Dip switch was still present on the bars but the horn press was missing- the flick to dip switch still worked.

Removing the switch revealed a lot of rust as expected but also a multiplicity of wires which was unexpected. I'd bought a replacement modern switch which sounds the horn by simply earthing through the handlebars. As such this requires only 1 wire for the horn (power to earth when pressed) and three for the dipswitch (headlight power in- and out to main or dip). The Quick 50 switch has 5 wires. 

Switch contacts once removed from cover. The centre contact has lost its screw.

The three for the headlight are as expected but there was an extra for the horn. I now understand that this arises from the AC induction system that provides power and the requirement to earth these coils when not in use. The horn on this bike is powered by a separate induction coil and of course is used only infrequently and intermittently. The horn power coil therefore needs to be earthed when the horn isn't sounding and this is achieved via the complicated switch present here. Power arrives at both the horn input terminals "K" and "H" on the switch. However in the rest position terminal "K" is connected to earth and so the voltage is dissipated. Power arrives at the second terminal "H" after passing through the horn but in the rest position this terminal is isolated. However when the button is pressed the moving contact disconnects from terminal "K" and connects terminal "H" to earth. Current thus flows through this circuit via the horn causing it to sound.   Hopefully this is clearer in the diagrams!

Looking at the standard wiring diagram, power was provided to both lights and horn  by  the lighting coil in the generator. I suspect this proved inadequate at some point since my bike is fitted with an extra coil simply to power the horn. However, I will consider how to deal with my setup once I have worked out how it is supposed to work in its original form so for the time being I'm considering the wiring diagrams as provided in the manual. 

In the standard diagram- power from the alternator is fed via a blue wire to t51 on the lighting switch which functions as a junction block to feed the horn via a silver/grey wire. Consequently this will be energised whenever the motor is running regardless of the position of the lighting switch. When the horn button is pressed current flows through the switch and horn and thence to terminal tH on the bulb holder by another silver/grey wire. Terminal tH then connects to earth. This is a junction block connecting the horn return to a grey wire leading to the horn switch (tH). When the horn button is pressed the moving contact is pressed against tH thus earthing to the handlebars completing the circuit through the horn and causing it to sound. Current path when the button is pressed is shown in green below.

Current flow through the horn when horn button is depressed (flow shown in green) independent of lighting switch position.

 

When the lights are "off"- i.e. switch straight ahead in the "run" position, T51 is still connected to the switch arm via an internal copper bridge which transmits incoming power to the moving terminal of the switch. This is then connected by the switch arm to an unnumbered terminal (51b?) and from here a brown wire connects to t51 on the bulb holder. This again acts as a junction block and continues to the horn switch tK which, when not pressed, is earthed via the handlebars. Consequently power from the alternator is simply dumped by constant current flow to earth. However, the coils will generate power whenever the motor is running and presumably arrangements are needed to dissipate that power to avoid any damage to the coil.  Of course both sides of the horn circuit will remain live at all times the motor is running as it is independent of lighting switch position- the only difference is through which side current is permitted to flow. 

The horn switch itself is very unusual for motorcycles which would usually have a single wire coming in from the horn, and earth this to the handlebars when pressed. The Quick 50 switch acts not only as a horn button but also as a current dump for output from the lighting/horn coil when the horn is not in use and this explains the extra terminal. In my case since the switch is broken I will have to replace it with a more conventional horn dip switch (3 wires) and thus I will have to arrange for output earthing in some other way or risk coil damage. Its further complicated since I have an extra coil purely to power the horn (prevents lights from dimming when the horn is operated?) which must mean I will need to arrange to dump output from the lighting coils too when the lights are not in use? 

In the meantime I fitted a modern horn button (no coil dump function) so that the horn will work and allow the bike back on the road. I'm not sure how best to arrange the coil earthing function and new NSU horn buttons of this type are no longer available. 

Should add that the output from my lighting coil is 12V AC and not 6V as stated in the handbook. It seems therefre that the lighting has been upgraded to 12V whereas the horn has remained at 6V as the output from the horn coil is 4-6 V AC only

Lighting switch (upgrade)

Although my repaired light switch worked well- there was no getting away from the fact that it wasn't meant for this bike and was too simple to perform all of the required functions. The problems are firstly that the lighting coil isn't being earthed when not in use (which can eventually damage the coil) and the kill switch had to be moved to an unsightly extra (modern) button on the bars. New switches are available but at 50 euro plus mailing they are just too expensive at present. Since an incorrect switch had already been fitted, I reasoned fitting a more functional replacement would be acceptable. I opted for the 9 pin Wipac switch as fitted to many British bikes. This has an odd connection block which is a somewhat bulky system so to save space I rejected this and soldered fly leads directly to the switch terminals, covering each with an insulation sleeve.

Wipac 780 switch- spade terminals intended to engage with connection block.

The stub of the switch is only marginally larger than the existing hole which can be carefully filed to size and profile and should permit any eventual refit of the NSU switch. I enlarged the hole creating a locating flat to the rear. This orients the switch fore and aft and the headlight retaining screw hole should act as a datum for switch position.

Switch in nacelle

The Wipac switch is capable of many different connections and the solution I adopted is given below. In each case I soldered a short fly lead directly to the switch and connected that to the loom via a bullet connector. I realise thats bad practice in a 6V system but I was concerned mainly at this stage with ease of nacelle disassembly. In each case below the first colour is the colour of the fly-lead (this is for my own records- obviously unless you have this actual bike its irrelevant to you) but the second colour stated is the colour used in my bikes loom. In a few cases I used the bullet as a junction to connect two wires. I'm numbering the terminals from 1-9 as so:- Holding the switch (terminals up) -locate the gap where 1 terminal is missing and orient it at 12 O' clock. The terminals are then numbered clockwise starting from that gap.

Terminal Connections

1 Black [bullet] Black (To Earth)

2 Pink [bullet] Blue AC (Power in for lights)

3 Green [bullet] White (Power out to dipswitch) 

4 -

5 -

6 -

7 Black [bullet] Black (Kill feed)

8 Black [bullet] (To Earth and Speedometer case)

9 Red [bullet] Red (Speedometer bulb) and Blue (Rear Light)

Wired in this way the Wipac switch gives three positions:

"O" Run with LIGHTS OFF -lighting coil diverted to earth

"L" Run with LIGHTS ON -lighting coil to lights

"H" Engine KILL -ignition wire to earth