Wednesday 24 April 2024

Fitting Mudguards …and a workshop accident

Fitting mudguards is not a particularly exciting topic but nevertheless an important task that if done carelessly can really spoil the appearance of a bike. In particular, mudguards of the correct shape and diameter should be fitted to give a constant or near constant distance between the mudguard and the tyre (although I recognize that this is not possible on swinging arm bikes where the relationship between the wheel and mudguard changes with the suspension and the rear mudguard needs to allow for wheel removal), and although it may be stating the obvious, the guard needs to be fitted to be exactly on centre with the tyre.

I get my mudguards in raw steel from Renovation Spares and with 21” x 3.00” tyres fitted to the bike, I use 29” x 4” and 30” x 4 ½” D-section guards on the front and rear respectively.

which then need to be cut to length and fitted. Simon, who runs Renovation Spares, has also put in 3/8” indents in both sides of the front mudguards to avoid interference with the girder forks.

Before any mudguard fitting takes place, it is important to check that the rebuilt wheels are on-centre and, for the rear wheel, that the chain alignment is correct. For this, it is necessary to put the gearbox back in the bike temporarily.

A new IWIS ½” x 5/16” chain is fitted. All OK here.

I have used ½” diameter thick wall (1.5mm) tubing for making both front and rear stays on all my recent projects and as far as I am aware this was how KTT 55 would have left the factory in 1929, as suggested by period pictures of Mk 1 KTTs and the brochure picture below.

However, the period picture of KTT 305 in the Isle of Man with Dave Brewster on board in 1931 (and the factory records indicate that the bike was sent directly from the factory to the IoM) clearly shows flat stays on the front.

Further digging has revealed the following from Ivan Rhodes book Technical Excellence Exemplified:

On Page 26 Ivan states that Works Velocettes left the factory with flat alloy mudguard stays at the front - that would explain the above picture.

There is another difference between the Dave Brewster picture and other contemporary KTT pictures and that is the existence of an additional horizontal stay to support the rear mudguard. The 1931 brochure picture, shown below,

 Acknowledgement to Ivan Rhodes Technical Excellence Exemplified

clearly shows a horizontal stay.

I will therefore try and recreate exactly what is shown in the IoM picture except that I will use steel rather than aluminium flat bar for the front stays because it is much easier to work.

I have used 20mm x 3mm flat strip for the upper stay and 25mm x 3mm strip for the lower stay. These bend nicely around an appropriately sized piece of round bar


and then, with some heat from oxy-acetylene, bent to follow the edges of the mudguard

using an off-cut screwed to a piece of wood.

This really needs 3 hands – one to hold the gas torch and the other two to hold the metal bar. For many years I have adopted the practice of sandwiching the torch between my left arm and my body to give 2 free hands for working the metal. This is not a safe practice and the dangers of this were brought home when making this bracket as I managed to pass the flame over my right thumb. Oxy-acetylene works well for bringing metal up to red heat quickly because, at over 3000 0C, it is the hottest flame available in the workshop …but it can really do some damage to flesh and skin!

After 2 weeks the wound is healing nicely but I shall be more careful in the future to avoid barbecuing parts of my body.

The front mudguard turned out OK.

Stays for the rear mudguard are made using ½” diameter thick wall tubing as I mentioned earlier. Although I have a bender for this diameter of tubing the radius of the bender is too small to give a proper fit around the outside of the mudguard. However, in the many offcuts of round bar that I have there was one that was a good fit for the mudguard and the tubing can be bent by hand without using a tube bender, as shown below. These are 1m lengths of tube and so there is plenty of leverage.

After shaping and cutting to length, the press tool that I had previously made for the 33/7Trophy project

was used to swage the ends. The first pressing is done in the vice

but this can’t provide enough pressure to close the end

and the 20-ton hydraulic press (using typically 6 – 8 tons pressure) is used to finish the job.

After drilling and rounding the ends

the upright stay is finished.

The part of the stay with the handle for hauling it onto the stand has a short straight section at the top and this needs bends of a smaller radius. These are done using the tube bender

before fitting to the bike and setting up for tack welding to the first upright stay.

The last part of this stay is the cross piece that connects to the mudguard.

Before tack welding this piece, the mudguard is clamped to the upright stay to ensure it is in the correct position when the attaching lugs have been made and fitted.

The lugs are made from 16mm x 3mm flat and are shaped

and bolted to the mudguard before tack welding with TIG.

….being careful not to weld the screw head to the lug!

After removing the stay to complete the welds, mudguard fitting for one bike is finished.


The frames were made sufficiently accurately 90 years ago that the mudguards and stays made for one are interchangeable with the others and I will use the rear guard and stays shown in the above picture for the cammy special.

Anyway, 2 more bikes to go….