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