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The BSAOC Technical Consultants

The BSA Owners' Club recognise that not everybody is an expert on all machines and because of this we have volunteers who have amassed knowledge on specific models or have special skills. These people offer help to our members for the price of a Stamped Self Addressed Envelope. Many members use these consultants when they are at a crucial stage in a rebuild or restoration, or even when their bike develops a fault.

Remember that advice is only given to members. So why not join?

We have Technical Consultants for the following models and skills.

A50 - A65 Oil in Frame and Hornet specifically. A50 - A65 pre Oil in Frame models.
A7 - A10 Swingarm models.

A7 - A10 pre Swingarm models.

A75 Rocket Three. Bantam D1 to D5 and Ariel Three.
Bantam D7 to B175. D7 to B175 Post Office machines.
Beagle. B25 - B44 - B50.
C11G - C12. C15 - B40.
M20 - M21. M21 Automobile Association specifically.
Gold Star. Pre Unit Singles.
BSA Sunbeam Scooters. Winged Wheel.
1914 to 1920 557cc singles. Dandy.
We also offer help with the following.
BSA Specials. Transfers.
Paints and Finishes. Machine Dating (using original factory despatch books). This service is available to non-members.

Many of our experts are consulted by the major Classic Motorcycling publications for advice .

As well as our experts we have 4000 other members, one of whom is sure to have come across your specific problem, a letter to our monthly magazine The Star will usually bring an answer.


Typical Questions and Answers from our Technical Consultants




Dear David,

I own a 1967 BSA C25 Barracuda and I would like to know if I could fit a Triumph 500 unit construction engine into my frame. Can you advise if this has been done successfully and what are going to be the problems I will have to overcome. Problems I suspect will be engine mountings, sprocket alignment and gearing. I have the standard single leading shoe front brake, will this be up to the job or should I have to source a double leading shoe brake.

Yours sincerely A N Other


Dear Sir,

This should be OK and make a sensible, nimble, machine. The C25 cycle parts are a result of BSA's motocross success in the sixties and a good package which had no trouble dealing with the B44 engine for starters and the Daytona engine is one of the few decent engines Triumph made. Indeed BSA did exactly this (using an OIF frame) in the seventies and called it the Triumph adventurer. HOWEVER I have not done it, or seen one, and this particularly makes me a little wary. The way to do these things is not to rush in and to solve all the problems before you do anything drastic or spend serious money. You will find that you will be compromising as you go, but that's ok, someone did that for production machines too. What you should be aiming for: 1) Gearbox sprocket as close to the swinging arm pivot as possible. (reduces variation in chain tension) 2) Gearbox sprocket, swinging arm pivot and rear wheel spindle in a line at half suspension load for choice, but certainly not so far out that the chain fouls anything throughout the suspension's range of movement (same reason) 3) Gearbox sprocket and rear sprocket exactly in line vertically. (No compromise here, should make your special function more efficiently than most old bikes!) However this is a relatively easy thing to alter the odd quarter of an inch so it's not your first consideration, as long as there's room for the tyre. 4) Engine weight down, forward and not too offset. (Sid Lawton was convinced that the alternator fitted to the Dominator was enough upset the handling noticeably) 5) Clean run on the exhaust possible (no problem for you), access past the frame for oil feeds, breathers, tacho drive, whatever. 6) Don't worry about gearing yet, but are the chain sizes the same? If not you may need to have a one off sprocket made; not necessarily the end of the world. 7) Clearance between engine and frame at all points except mounts. I suspect that the fit will be tight and that you will have little choice where it ends up. Unit specials usually involve some moving and welding of engine mounts which you must either be sure of doing well or accept you will have to pay for. On the other hand the primary drive is automatically in line so it's not all bad. Just bear in mind that if you don't want people mentioning Meccano in your hearing you will have to do your engineering neatly. No lash-ups if you are at all sensitive, because people WILL look at a special and they always critical. My aim is to make the beast look like it is factory built; if a solution looks a mess I rethink. If you already have the engine do some measuring. If you haven't, go to a show, the local Tri. OC meet, even a museum and chat them into letting you measure things. Best of all is an autojumble where you should be able to find a bare engine. Watch out for protruding castings that may cause trouble too. Write it all down, go home and have a think. There will probably come a point where you think the odds are good enough to buy an engine, remember you can always sell it! A set of scrap cases is a useful find at this point; you can continue experimenting without getting in deep. I think the thing I would be most worried about is the bottom mounting which might be a sod to work. You can't easily mod the frame there and it would be a pain to shorten the engine's cast in tube, yet this is probably the most important engine mounting of the three and needs doing carefully. So will it fit, with or without spacers? (With would be best cos then you can shuffle the engine sideways for the chain's benefit) I think I would be prepared to start from scratch with new front and back mounts to get the bottom one correct. I could write a small book on this. I hope that's enough to get you going; do some thinking and come back to me when you've got a bit further. Yes buy a TLS brake you won't regret it. Final thoughts; it might be as easy to buy a later 60's triumph frame as well; the forks will go straight on for starters, and they had the handling sorted by then (indeed the 500 frames look very like BSA ones, probably no coincidence), alternatively the scrambles boys are dumping Rotax engines these days. No I've never seen one of those either; read my notes above! A B44 engine will go straight in, a B50 (nice) will need the rear engine mounts moving. 'Triumph Tuning' by Stan Shenton is a brilliant dirty fingered book and worth buying, if still available, for the general principles, let alone if you want to tune a triumph. No you can't borrow my copy. Good luck.

Best Wishes,

David Gardiner

BSA Owners' Club Technical Consultant (Specials)


Dear Andy

Could you tell me what the markings on the D14/4 headlight switches stand for and which position they should be in to work? Also how does the emergency starting position work.

Thanking you in anticipation,



Dear Lawrence, thanks for your letter about your D14/4 headlight switch's.

The light switch, (which is on the left of the headlamp), 'H' is on the left & 'L' on the right.

The ignition switch,(which is on the right of the headlamp) 'I' is on the left & 'E' on the right.

These are viewed sitting on the motorcycle.

Putting the ignition switch on Emergency position just connects the extra two coils into the charging circuit, this is also done when the headlight is turned on, therefore, the bike wouldn't be overcharging unless the lights were turned off. Both switches are the same, BSA didn't make two types (cost cutting !) When the manual says 'rotate switch to right', the position should be that the letter (H,L,I,E) required is pointing straight forward, hope this is of help

Andy Lorenz

BSA Owners' Club Technical Consultant (Bantam D7 - D175)


Dear Andy

I have some Bantams which I would like you to help me find the original specification and colours for. I have a couple of machines, the D7 has some blue on the side panel, do you know what the exact colour is? What colour seat should be on the D7? I include the engine numbers of both bikes

Engine ED7B-2416

Engine YD-80439


Dear Andy, thanks for your letter. Engine YD-80439 is a D1 125cc from 1952, Engine ED7B-2416 is a D7 175cc Battery engine of 1959, the model will be identified by the frame number,

1959 D7-101

1960 D7-8101

1961 D7-18401

Colours are as follows, for the Tank, sidepanels and mudguards 1959 Royal Red or Black, 1960 Signal Red or Sapphire Blue or Black, 1961 as 1960 with option of chrome tank sides not ivory The light Blue on your side panel could be Sapphire Blue from 1960 the best person to talk to on colours and paint is Polly Palmer from Bri-tie Motorcycles (details in the Star). The seat is a light grey colour, I am not sure if it is two-tone. Hope this is of help

Andy Lorenz

BSA Owners' Club Technical Consultant (Bantam D7-D175)