Page 83 - 100% Biker (January 2020)

Now here’s a thing. Remember how I discovered the bent-in tubing behind the
headstock cover hidden by a plate? Well, here’s the second surprise of the build.
I didn’t expect to find a second bit of tubing coiled inside the first when I cut the
frame open. Maybe someone from their days at BSA factory knows better, but
the only reason I can fathom out is that the inner tube was pushed inside to act
like a mandrel when the frame tubes were originally bent at the factory.

Bear in mind that, at each side, it’s one piece of tubing from headstock, right
under the engine and up to the seat, some six feet or more, so it might be a
cheap and cheerful way of stopping the tubes kinking. It goes some way to
explaining why BSAs are so heavy, too.

It did pose me a bit of a problem, though. In a high stress area like that, I like to
sleeve tubes on the inside before I weld them. Two reasons for that; it potentially
adds strength (there’s an argument that a properly welded tube should be as strong
as an unwelded one, although I’ve never been convinced), but also it adds durability.
It’s all a matter of stress and vibration. My theory is a solid slug inside a welded tube
tends to ‘soak up’ the harmonics. But how to fit a slug tightly inside the tube like
Eventually in any project you reach a point of no return. This is it. Courage, conviction and commit- this? In the end I used a bar to uncurl the inner tube as much as possible, then made
ment, the three Cs of bike building. I’ve taken the swinging arm out for this shot as it makes it more a tapered slug which I could hammer down the inside with some force, which would
dramatic, but while doing any actual work I’d kept it bolted in place. That meant everything was push the tubes out tight against each other. Not perfect, but I was also aware I’d be
always held in two places, so the original datum was constantly preserved. bracing the outside as well, so I was happy enough this was an acceptable solution.

’m doing this because once
I started planning it all, it
quickly became apparent that
extending the carbs back and
I fitting decent filters would
mean they picked a fight with the
original frame tubes behind the
engine—I’ve still not mastered
the art of getting two things in the
same place at the same time.
Furthermore, the alloy oil tank
I scored off eBay mounts on a
single central frame tube, and if
I did do that, I could use smaller
rear engine plates and save weight
while making it stronger. I also
wanted to disguise the original
frame’s origins as much as
possible, just for the fun of it. Plus,
I just like cutting things up.
If you subscribe to the opinion
that our entire motorcycling
heritage is sacred, it’s probably
best not to read on. As you may
be able to tell, I don’t. I do what
motorcyclists have always done
(particularly but not necessarily
when they want to go racing),
I enjoy turning ordinary bikes
into unusual bikes. I’ve been
doing it for a lifetime now, ever
since I took a hacksaw to my field
Bantam when I was 11. And it
appears I’m still cutting up BSAs First side done. I was undecided about making new seat tubes as well, but in the end the original ones
over 50 years later... were more or less in the right place, so I decided to leave them. All I need to do now is the other side...

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