Advice on a BSA B40 project

[bpilgrim]

Hello,

I'm after some advice about a BSA B40 trials project. I'm a 19 yr old engineering student and have almost completed my first bike restoration of a Montesa Cota 348. It was a fairly simple bike, but I have learnt a lot and I think it's time I took on another project. I want a British bike, (which I wanted initially, but thought I'd start on something simpler and cheaper!). I want to use the bike for trials, so the B40 comes to mind. (The C15 seems a nice bike too, and is probably better for trials, but I'd much rather have a 350cc)

So in a few months time I will be looking to buy a BSA B40 for restoration. It doesn't have to be a runner (I'd actually rather it didn't run, just for the thrill of getting it running!) and I plan to turn it into a trials machine, and so I am not too fussed about whether it has the tinware, tank, mudguards etc. One thing that it must have is matching frame and engine numbers, I know the numbers aren't that important, but I have a 1971 Land Rover that I bought when I was 16, which doesn't have matching numbers, and it bugs me little...

I am therefore after some advice on how much you think a B40 would cost, in complete mechanical condition, with matching numbers.

I'm also after a bit of help with turning it into trials trim. I know some people take the modifications really quite far and get quite technical/competitive with Pre-65 bikes, but I just trial for fun and so I want to keep it fairly standard. (Here's me now being picky and patriotic) I set my 'modification limit' at not making any permanent or irreversible modifications whatsoever, I also wouldn't go near electronic ignition, or use parts off foreign bikes (e.g. Montesa fork internals and definitely not a Mikuni carb!), I'll run it with the standard Amal monobloc carb and standard spark plug too, which was possibly a Lodge? I like keeping it fairly standard because I like learning about classic bikes and tinkering with the points and the timing, and playing with the carb.

These are the jobs that I am currently aware of to get it from road trim into trials trim:

- Fit aluminium mudguards, tank, and a small seat (or just make a plate and put some sticky foam on it)

- Fit high level exhaust from Sammy Miller. Quite a few B40s/C15s don't seem to have silencers on the high level exhausts, can I run it straight piped? Are they really loud when straight piped? I'd like a loud BSA! Also, if I can use a straight pipe, will it burn the exhaust valves, maybe need a richer jetting?

- Tyres, I believe both front and back road rims are 18", are these rims strong enough for trials? Is it possible to get a suitable front trials tyre for an 18" rim?

- Oil tank, I've seen a C15 scrambler with the standard oil tank on ebay, but most seem to have slimmed down tanks, or oil in frame, what is the benefit of oil in frame?

- Sump guard, plan to make an aluminium one

- Handle bars, I would assume the road versions are unsuitable for trials. So new trials bars, 6" rise ish?

- Gearing, I think I've read that the gearbox has a lower range on trials/scrambler models, but can this not just be done with a small front and a large rear sprocket?

- Suspension, would the road setup be ok for trials?

That's probably enough questions for now!

Many thanks in advance,

Ben

[alan_nc]

Start by picking up a copy of the "Rupert Ratio". Once you have read that you will have a much better idea of how to go about the project.

[davetom]

Hi Ben, well I`m sure you`ll get much more knowledgable guys than me along soon to assist you but until then...

1st of all, I understand your feelings on matching engine/frame numbers, but you will save lots of cash if you just get the best engine you see, and any frame. That is pretty much all that will be left of use to you anyway, should you buy a complete bike. If you plan to use steel rims, the back is fine but you need a 21" front. They were used back in the day so its original enough.It will be difficult to build without at least modifying the rear subframe to lower seat height, though the material you remove could possibly be put back in?

Dont bother with a straight pipe, they are loud enough with a token silencer, you`ll annoy yourself in the end ,and all around you.

Oil in frame or alloy oil tanks are to remove weight and bulk.

For bars, just find some Renthals on Ebay, or trawl autojumbles for steel ones if thats what you want.

Your correct about the gearing, my C15 is 15 front/59 rear, but you`ll struggle if you plan to use standard hubs, they are heavy and there isnt much choice on rear sprockets.

The standard shocks are not suitable, you want some a couple of inches longer at least to get you some ground clearance.

You will need fold up footpegs as a safety requirement too, mounted further back and higher for traction/clearance.

I dont want to pee on your bonfire, its great that you have an interest in British stuff, but costs mount up to make something trials suitable, it would save a lot by buying something that has had some of the work done and needs improving. I converted a standard C15, and there is only the frame and engine still original.If I were to do it again, I`d get something that someone else has thrown a bit of time and effort(and expense!) at.This is without loads of "fiddle" mods either, the reason that people deviate from standard road bits isnt to cheat, its just that the road stuff is not fit or suitable off road.

Well good luck and I`m sure you`ll get any questions /querys answered on here, they`re a friendly knowledgable bunch.

Dave

[matchlessman]

I'd echo the above.

Make it as light and robust as possible. You will spend quite a bit of time picking it up after you've thrown it at the scenery in the beginning.

Nothing more frustrating than falling off and breaking something that ends your day, and nothing worse than at the end of the day just wishing it would all finish because you're knackered after fighting a heavy heap of junk through every section.

The mods are to make them steer, brake and go. There is no point in giving yourself an impossible task, you'll end up hating it and selling before you've even got going.

Go to a trial, take pictures of the bikes, talk to the owners, they'll tell what is essential to make them rideable and what only gives a marginal improvement. More importantly they'll tell you where to focus your attention and cash. For instance you'll need to budget a minimum of