quarter incher

Get yourselves one of these 1/4 inch Whitworth spanners and keep it in your "don't-leave-home-without" tool kit. For one, you need it to undo the banjo bolt on the Amal carburetter.

Rear wheel: quick update.

The gorgeous conical hub and its brake plate have gone off to the machine shop to be sandblasted clean.

Should look pretty good when done.
I took the rim, spokes and nipples to the workshop. The rim cleaned up real nice with a brillo pad and I was pleasantly surprised to find that the chrome plating is in much better shape than I had thought at first. There are only a couple of spots where iron oxide has bitten hard but not enough to warrant having the whole thing re-chromed. There's something else to be said regarding re-chroming rims: very often, if you see a lot of oxidation on the rim, chances are it will have built up inside the rolled edges (where the tire sits) and there is no way to really get in there and get rid of the rust. So you could have a perfectly shiny rim and a bunch of rust on the inside.... would you like that on your bike? Thought not.
The rear wheel will be built up pretty soon. Things have started to happen, it's exciting at this stage because although it's small things that go slowly, you know they'll lead to progress (and it's exciting because we still haven't run into any problems so we're not jaded yet - but give that time). From now on, parts will fit together to make a machine that moves. How cool is that, really?

Score!

So, in addition to the single-carburetter A50, BSA also made a twin-carb version of the 500cc for competition. It was called the Wasp (but there was also the Cyclone - little difference I think) both in scrambler and in road going trim; not many were made compared with the standard version so it is somewhat of a rarity compared to the twin-carb 650s.

Really, the most important component of this version is the cylinder head, which has the twin port for two carburetters. Visually the biggest difference is in the space between the two combustion chambers, about two inches on the 500, whereas there's hardly any meat in between the 650's head.
A few months ago I was browsing around for spares when I came across a spares dealer (NOS and new) that had one up for sale at a very reasonable price and in good nick. I jumped at the chance and now I have the option to transform the engine into a fire-breathing twin-carburetter beast if I should find that the standard head doesn't have enough go.
What the heck, I just like having it sit on my shelf for now!

A bit of background.

Here's what I know about the engine's provenance: it was bought and sold at least a couple of times, the last of which was at one of the regular classic bike autojumbles where blokes go rummaging in big grimy piles of dirty, rusty, sticky, oily metal sitting in the open air, in the baking sun or under the pouring rain.
As I mentioned before, I have no idea why the engine became separated from the rest of the motorcycle in the first place, but judging by the way it seems to have been severed, I'd say it was probably done at a breaker's yard? Or perhaps the bike was in an accident and they salvaged the engine? Maybe they had a 650 engine and swapped it out?
I doubt I'll ever find out, though I might get in touch with the owners club and see if they can trace any history based on the engine numbers. Then again there are only slim chances of that yielding any results seeing as, from what I gather, BSA engine numbers are more of a rough guide than a precise indication.
What I know for sure is that many people have had this engine, but few of them have actually used it. It just sort of got passed around until it reached me - and even then, it's been sitting in a workshop half dismanteled for a good while now.

'sploded view

Behold! And learn all the secrets of the Amal Mk1 Concentric!
How glorious are vintage drawings?
There is only one small piece not shown (or possibly shown within the air slide spring) which is a small brass tube in the shape of an elongated top hat: this fits into the spring, into the air slide.

Features for 1962.

You really do get the best of everything with a BSA!

the old '626'

I took apart the A50's original carburetter to see what was inside and get an idea of jetting and needle position.
When BSA originally produced the first 500 unit twin, they fitted a 1 inch Monobloc, which was then superseded by the Mk1 Concentric when the Monobloc line was discontinued. Switching from inches to millimeters, the 26mm was the closest to the 1 inch measure.
I'll fit another carburetter altogether but I kept this one for the original air filter and as a source of float-bowl screws (you can never have too many of those, trust me.)

Look at the petrol pipe feed and the throttle cable sticking out at the top: my guess is this was chopped off the bike with a pair of wirecutters when the engine was removed. Now, why the engine was removed from the original bike, we will never know. 



All the bits are there, further proof that this thing was just ripped off the original bike together with the engine - to which it was still attached, air filter and all, when I got it.

But what's this? The float needle is of the modern viton-tipped variety as opposed to the original all plastic kind. This would suggest that at some point, someone opened this up and changed it.

The stampings at the bottom of the slide are "622" and "3 1/2"

The needle is marked with two thin grooves on the head (these are not the ones where the clip goes, Amal needles come in several different types, identified by the markings on the blunt end of the needle) - the clip is in the 1st groove (or 3rd, depending which way you look at it) meaning that with the throttle off, the needle sits high in the jets assembly, allowing more fuel through.
This is one of several things you can tune on the Mk1 and they each make a difference. Do not be fooled by the apparent simplicity of the Concentric, for therein lies the brilliance of this design. You don't need anything more (pointlessly) complex than this, and you can tune them to suit your engine perfectly.

The main jet is a 200 and I don't even want to guess what that freaky residue is inside it. Probably something organic left by insects. I had just ran out of WD-40 so couldn't get the jet holder off to get to the needle jet, which I'm guessing is probably a 104 or a 105.

Speaking of insects, what the frak is that?

Definitely not in the Amal parts list.

"eeh GOOD news everyone!"

If all goes well the engine rebuild should start in the first week of December, so not long to go.
It all needs to be taken apart and properly rebuilt. Sludge trap, bearings/bushes, etc.
Nothing extravagant at all, no exotic bits, at least not this time around. Standard specs, possibly just a rebore if needed.

I'm not gonna lie to you...

I'm not gonna lie to you guys, this thing is going to take a LONG time. Why start a blog if I have barely started to do anything on this bike?
Yes, it would have been much more satisfying for everyone to see it done, from start to finish, without having to wait for ages for a new post, etc.
Well, first of all I doubt there are too many people following this, mostly I wanted to have the blog name secured and be able to document the build so I could share it with a few buddys once it was all done.
So, sorry to keep you waiting, I'm more anxious than anyone to do some miles with this thing!

It's the simple things, you know?

So, first of all what is this thing?

A chopper, a bobber, a hardtail, a chop, a custom-built, lanesplitter, garage-built...
There are so many labels flying around that I don't want to waste too much time finding one that suits. I'll let you all decide for yourselves what it is, once it finally hits the road.

the A50

"In the beginning, BSA created the A50, and saw that it was good..."