Monday, 14 June 2021

Footrests and Rear Brake

The footrests and rear brake arrangement on the donor chassis, the 1931 AJS SB8, were of no use for the V-Twin for 2 reasons. Firstly, the footrests were fixed to the engine plates between the engine and gearbox and there is absolutely no space for such an arrangement here and, secondly, the Royal Enfield shock-absorber hub that I am using in the rear wheel has the brake on the right side and this requires a cross-over shaft for the footbrake pedal for the pedal to be located in the usual place for a vintage British bike on the left side.

So, the question arises as to where to mount the footrests and how to arrange the brake….?

The solution that I adopted was to mount 6mm thick steel plates on both sides of the frame and attached to two of the three 7/16’’ diameter high tensile studs that fix the front and rear parts of the frame together. I was also able to support the plates at the rear using a conveniently positioned frame lug that was present on both sides and in exactly the right place to give the plates a 3-point fixing.

I had, for one of my previous Norton Model 18 projects, purchased a pair of original WD (War Department) Norton footrest hangers on ebay from a guy located in Australia. If you want to get any then the company name is Trojan Classics ….but be quick because there probably aren’t too many left. Norton used longer footrest hangers on their vintage bikes but the WD Norton hangers are shorter.

I decided to use these here because they can be conveniently rotated in 30 degree intervals to optimise the position. They arrived, still wrapped in the grease and paper from when they left the factory, and probably haven’t seen the light of day since 1943. It is a mystery to me how bucket-loads of WD Norton footrests ended up in Australia but, as of the week of writing this blog (15th June 2021) the UK and Australia have just signed a free-trade agreement, so maybe we’ll be able to make these a core export in the future….

and after a bit of degreasing, they emerged as good as the day they were made.

The hangers need fixing to a similar 30 degree indexed mounting and these were made in the milling machine.

It is interesting that such a complicated setup is needed for such a seemingly simple component.

Two of these footrest hanger attachments were made with a shoulder to positively locate them into the 6mm steel plates, which had been cut to shape by making a cardboard template, and were then brazed to the plate.

The next step was to make the crossover for the brake. A consequence of having the brake pedal on the left side whilst the brake itself is contained in the hub on the right side is that the brake rod connecting the brake arm on the brake pedal shaft to the brake operating lever on the brake plate would need to be positioned on the top of the brake arm to have the rod in tension (pulling). The picture below illustrates this on my 1928 Model 18 Norton.

There was not sufficient space to use this arrangement for the V-Twin and the lever needed to be positioned below the spindle. A result of this would be that the brake rod would operate in compression (pushing) rather than in tension if the brake arm was fixed onto the end of the brake pedal shaft. It is not really a good design to have a control rod such as this operating in compression as it would be subject to buckling loads and there is a good chance that it would bend in the middle if any substantial pressure was applied to the brake. There are 2 possible ways to solve this: either use a thick brake rod (typically 3/8”) if it is to be in compression or reverse the direction of “pull” and use a ¼” rod in tension.

I chose the latter route and this necessitated using an additional shaft and a pair of gears to change the direction of rotation. The picture below shows the collection of bits necessary to achieve this.

Here, there is a brake pedal mounted onto a 11/16” diameter shaft as a tight interference fit and also held on with a ¼” high tensile bolt and is silver soldered. The other end of the shaft has a ½” square machined onto the end onto which is fitted (a light interference fit so it can be assembled) a 20 tooth gear. There is another gear mounted onto an adjacent shaft (this was subsequently silver soldered to the shaft) which fits into a short housing containing a grease nipple. The gears are off-the-shelf items and come with a 1/2'' hole; this needed spark-eroding into a 1/2'' square. On the end of this shaft are 12 splines onto which is mounted a brake arm (ebay find from a BSA C15).

The picture below shows the assembled collection of bits. The brake return spring is yet to be added.

One issue that is yet to be addressed is the footrest on the right side. I would prefer to have a kickstart on the bike rather than having to run and jump on ….I’m getting a bit old for that, but with a footrest in a fixed position there is no chance of having a kickstart.

I found a pair of folding pillion footrests and modified one of these to screw into the 7/16’’ BSCY thread on the Norton footrest hanger.

The picture below shows the modified footrest (upper) together with the unmodified one (lower)

The complete collection of bits is shown below. There is now the addition of a brake return spring (Triumph T100) and the spindle support housing has 16 holes to enable the spring to be positioned optimally.

The plates have been trimmed to eliminate unnecessary material.

The assembly, ready to fit on the bike, is shown below.

With the addition of a brake rod and a knurled adjuster knob the complete kit is now mounted on the bike and works as intended

….but it turned out to be quite a lot of work for a couple of footrests and a rear brake.


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