Monday, 5 September 2016

Missing Speedometer

One of the things that always seems to be missing from my projects is the speedometer. Fortunately I guess all my bikes have chronometric instruments, which do not attract the exorbitant prices of the PA speedos, but nevertheless they are not cheap!

The W/NG was no exception. Fortunately, the drive gearbox is there:

It works, but looks like it is full of crud; the small pinion 5246-38 is missing:

The big one is there though:

The gearboxes are easy to clean out. The two spindles are both retained in place with a pressed plug, a bit like the core plugs you might find in an engine block. The one on at the end of the horizontal spindle, that goes into the hub has a grease nipple; the vertical one, that drives the cable is retained by a split pin.

These gearboxes are available in a variety of options:

  1. clockwise in/clockwise out
  2. clockwise in/anticlockwise out
  3. 12:8 ratio
  4. 14:8 ratio

And probably many others. They are quite straightforward to dismantle, though the cast bodies are brittle. Remove the split pin and tap the end of the cable drive spindle with a 1/4" punch - the spindle will push the plug out with it; do the same for the other spindle. clean all the old, hardened grease out and reassemble.

We'll have to buy a cable. It will have a spade type drive:

The small pinion is readily available from our favourite Suffolk spares stockist and is fitted after the gearbox is mounted in the brake plate. I used a split pin, making sure that the legs were trimmed short enough to disappear into the groove around the pinion

Here it is in place. You can see that when it is the proper position, the groove is enclosed in the brake plate and there is little space:

The speedo head is missing of course. I have bought this one from eBay:

It's in very nice, patinated condition and has a light and a trip, unlike the proper S433B military one; but this is more useful to me so would make a sensible choice.

It will need some brackets. 1942 bikes like mine have the separate speedo brackets (5213A-41 and 5213B-41) as shown in the 1943 parts book:

These are the brackets I need:

These are also shown in the 1941 parts book with a different illustration:

So to replicate these brackets, we will make some dummies with 3/4" wide strips of cardboard:

The strip with the two screws mimics the fixing screws on the back of the instrument:

Wondering if I have this rear bracket upside down. I've realised that it doesn't look like the parts book...

The 'upside down' theory seem s to be born out by these excellent pictures of 'Burney' a fire-damaged W/NG being resurrected by Vincent van Ginneke of the AOMCC:

You can see that the speedo is a 90 degrees to the front leg of the girder

Top view shows relative position of speedo and headlamp
So let's try again:

Cut a slice of 3 mm thick cold rolled sheet steel, 16.7 mm wide as described by Vincent, not worrying too much about the length at the minute:

Its the bends that matter. Put the piece in the vice and make sure it is perpendicular to the vice jaws:

Two 45 degree bends give us the profile we need:

Clamped in place:

Two holes drilled for clearance on 1/4" bolts:

We will trim up and round the ends when we are finished. No point in doing that until we know it is in something like the right position. Here's my W/NG alongside Vincent's - looking very similar:


So here we have the second bracket, bent up and drilled:

And now, completed brackets waiting for paint.

Compare the W/NG at the museum. Looks like bracket is twisted; mine needs the corners removed!

And another view:

This one looks like it is further from the machine centreline:


  1. Hi ! Thanks for sharing your restorations!
    I have a Ariel 350 wng and i need the gearbox 5242-38 to put in wheel hub. What is the ratio of this gearbox? Thanks in advance!

  2. I think they are 8:12. Have a look here: