Wednesday 7 April 2021

The Mudguards and Oil Tank

Over the years, I have established what has become a well-trodden path for fitting mudguards; not so for making and fitting oil tanks, as will become clear.


The original AJS record attempt bike did not have any mudguards. That was fine back in 1930 when they were attempting to win the world speed record but not so good for riding around todays roads in the UK ….because it is illegal.  The bike will be run with open exhausts, which will possibly attract a bit of unwanted attention, and the absence of mudguards would only compound any consequential “issues”.

Vintage bikes, including the original AJS world record attempt bike, have a very “skinny” look – large diameter and narrow wheels, thin mudguards, narrow petrol tank etc which stems from the early days of motorcycling. I like this lithe appearance and wanted to preserve it in my recreation, even if the rest of the bike is dominated by a bloody great engine!. The wheels were already “skinny” – 21” front and rear and the mudguards were chosen to match these; specifically 4” across / 29” diameter for the front and 4 ½” across / 30” diameter for the rear. I have been getting my mudguards from Renovation Spares (contact Simon at for many years – all my recent restorations including the AJS K7, the AJcette and 2 Model 18 Nortons use their mudguards. The mudguards come in freshly rolled raw steel which then needs to be drilled and cut to length accordingly.

 I’m sure everyone that fits mudguards has their own way of making brackets, stays etc. I make mudguard brackets by bending a piece of 3mm thick steel around an appropriately sized cylinder and then using a section of mudguard chopped off the original (there is plenty there) as a former to “push” the bend of the bracket into the corners. This particular bracket is for the rear mudguard that is bolted directly onto the frame tubes on either side.

This need quite a bit of localised heat with
oxy-acetylene to get it red hot in the right place.

The front mudguard stays on vintage bikes up to ~1929, certainly AJS and Norton, often used simple ¼” diameter steel rod; in later years, thicker, usually ½” diameter tubing was used. I decided to use the thinner option here for the front stays which were made from ¼” diameter steel with an “eye” at the end to enable them to be screwed to the bracket; this approach is simple, cheap, light and effective and is identical to the earlier AJSs.

Again, quite a bit of concentrated heat in the right place is needed to form these ¼” ID “eyes” bending them around a ¼” steel rod.

On the rear mudguards, I use ½” diameter thick-walled tube. These are more substantial than the front because the rear mudguard needs to support the weight of a rider on the bump seat and the rear mudguard stay is often used by the rider to pull the bike onto the back stand, although I don’t plan on using one for this bike.

Some restorers flatten the end of the stay in a jig and then drill it to hold it to the bracket or frame. The thick-walled tube that I use is a bit too thick to flatten with a good appearance and I machine “ends” from mild steel that are inserted and silver soldered into the tube. The picture below shows the collection of “ends” for the rear mudguard before attaching them to the tubes.

The bottom “end” is made from 2 parts that have been TIG welded together.

The whole assembly of mudguard, brackets, tubes (appropriately bent to shape) and the “ends” are then assembled in exactly the right place and each tube and its “end” are tacked together with the smallest of TIG welds, shown below.

This is sufficient to hold the assembly together so that it can be removed and each of the “ends” and tubes are then silver soldered to make a permanent and strong fixture. After trimming each mudguard to length, the fabrication of these is now complete.

Oil Tank

The original AJS speed record bike has an oil tank clearly visible on the right side sandwiched between the upper and centre frame tubes.

and this is where I planned to put the oil tank. But how to make an oil tank?

As I have mentioned in previous posts on this blog, I am not a sheet metal worker. Yes, I can weld and braze a couple of pieces of sheet metal together but I have neither the experience nor the sheet metal specific tools for making the compound curves that are required here.

The alternative is to find something that already has the curves and about the right shape and size and to re-purpose it accordingly. I eventually decided that a Royal Enfield Bullet toolbox would be about right and bought this one

on ebay for £28. There are plenty of these around so one in good condition can be bought cheaply.

The plan was to use the nicely curved front in which would be the brass outlet and return fittings and the filler cap neck and to add a back and brackets.

The first step was to have the toolbox grit blasted and see if would fit in the available space.

Although a snug fit, it seemed that it would squeeze in nicely and so the next step was to start making fittings. The first was the neck for the filler cap. This was machined on the lathe from a solid piece of brass to fit the filler cap …another ebay find.

A cardboard template with the approximate curved shape of the filler neck/oil tank interface was then cut out of cardboard

and the neck was marked in white paint and cut out approximately on the milling machine.

It was then finished with a file and dremel to fit the tool box front.

Fittings were then made for the oil feed (which uses the original hole for the toolbox locking screw) and the oil return, into which is silver soldered a length of copper tube to bring the outlet up to the top of the filler, and a section of the sheet metal was removed from the top for the oil filler neck.

The next stage was to attach the back – which was the original tool box back reduced in depth, brackets to attach the oil tank to the frame and the filler neck using both braze and silver solder.

Unfortunately the heat and/or the attachment of the neck to the tinware distorted the filler neck so that it ended up oval  -  in fact about 1/8” out-of-round on the diameter and there was no way that the screw top would fit. It was either a case of throw it away and start again (not a good option as I had already spent about 3 days on this and there would be no guarantee that the same problem wouldn’t happen again) or try and fix it.

I squeezed it back to a round shape as best as I could in the vice but this is nowhere near accurate enough to screw in the filler top. I ended up making a 1.6” diameter tap using mild steel (it only has to work once – on brass) and managed to get this started on the existing thread to recut the thread. The “tap” started off as a taper tap and, as I was able to get it in further, was faced-off to eventually turn it into a plug tap.

Pretty crude but it worked and I was able to get the tap screwed right down

Such that the filler cap would screw into the thread properly


At this stage I could try it on the bike

Not too bad!

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