6 cont'd. Inlet Stubs
Inlet Stubs for 32mm Flange Fitting Amal 10TT9 Carburetors
Actually, I would like to see a real pair of early Black Lightning inlet stubs, just to see what they look like and what bore they are. If you look at early photographs you can see they definitely made some for flange fitting TT carburetors, however I doubt these were ever bored to 32mm. I would like to see if they are production items, or easily identified as one-off's. If anyone has more information I would be interested to know. I do have photographs of the bike in the National Motorcycle museum, fitted with these stubs, and they do look quite well made (I shall have to go back there and examine in more detail).
|When I came to make my own, the first
thing I needed to decide was if I should make a pattern and have them cast
in aluminum or fabricate them from steel. A few years ago I had acquired
a set of Series 'D' stubs, which are aluminium and are made to accept Amal
Monobloc carbs. I was hoping I might be able to bore these out to 32mm but
when I looked closely, it was clear that even if they did bore to this diameter
(which I doubted), they would be perilously thin. I also think that the
racing stubs, certainly for the front pot, were designed to give a more
direct (downdraught) path for the fuel. As the flange on the Monobloc is
the same as a 10TT carburetor, what this did tell me was that making my
stubs out of aluminium would very probably make them too thin to hold the
carburetors without the risk of fracture.
One good thing with this plan though, was that I would not have to make wooden patterns for having the stubs cast, which I really was not looking forward to.
|Fabricating Steel Stubs
Not suprisingly, I decided the easiest way to make the stubs was to find some steel tubing with an internal diameter less than or equal to 32mm. Unfortunately, despite contacting numerous pipe suppliers, I was unable to find any that met this specification, so in the end had to resort to using solid bar and boring it on the lathe to a 32mm internal bore.
For the flanges, I had available a length of xxmm X xxmm steel bar, from which I cut 4 individual segments using my power hacksaw. (For anyone who has ever had to cut large pieces of steel using a hand hacksaw, they will appreciate what a godsend a power hacksaw is!). Once the blanks were cut I then mounted each flange on the lathe and bored them to just fractionally larger than the external bore of the tubes. By making these flanges a loose fit over the tubes it would allow me to position them enough to achieve the correct angles (see accompyning photograph).
Once the tubes and the flange blanks were cut I then positioned them
between engines and carburettors, using archive photographs of early Black
Lightning's as reference to find the correct position. Once I felt I had
achieved the correct position I marked the blanks with a scriber and used
copious quantities of Blu-Tac to hold them in place while I removed them
ready for brazing.
|I then braze welded each flange to
the tubes, taking care to make sure only enough braze was applied to build
the fillet between the metals, so it looked similar to an aluminium casting.
The nice thing about brazing, as opposed to welding, is that braze has very
good gap filling qualities, so providing the parts were well fluxed, the
braze would easily fill the gap between the pipe and flange.
Carrying out this job took the best part of a day all told, but it was well worth it. Once each stub had the blank flange's brazed to the tubes, I could then offer them up to the heads/carbs once again, and scribe the final position of the oval flanges on to them. It was then a simple task of applying elbow grease, to hacksaw and file the flanges to shape.
Final job was to drill the holes on the flanges for fixing to the heads and securing the carbs. The heads had studs in place, so for the this side it was simply a case of drilling clearance holes. For the other flanges, these would hold studs, so they were drilled and tapped to accept 5/16" studs.