Monday, 25 January 2010

BSA A50/65 wiring loom in colour

Call me a sentimental old git, but I couldn't resist redoing the wiring diagram in colour. You can download the hi res version on:
To my utter amazement, six people downloaded the black and white version. How did they even find it?

Saturday, 23 January 2010

De-rusting with electrolysis: the details

This is such an interesting subject I am putting as many pics and details up as possible. I got the idea from Mike Brown's excellent 2009 book Building Budget Brits, which is essential reading for anyone fool enough to own a Triumph or BSA unit twin.

Here's the method.

1. Shake nuts, bolts or gravel around in the tank to dislodge any big flakes of rust. Use a cement mixer if you have one. Remove with old vacuum cleaner.
2. Make up solution of tablespoon of washing soda to a gallon of water.
3. Bung fuel filler holes with Blu Tac and fill tank to brim.
4. Hook up a battery charger, negative lead to the tank body, positive lead to an iron anode suspended over the filler hole, in the soda solution but not touching the tank.
5. Some chargers have cutouts that won't let them pass current when used like this. I used an old mobile charger delivering 500mA max.
6. Leave it fizzing until the reaction appears to stop. It was a few days for me (plus a couple of weeks before I had time to work on it again), but heavier current might speed it up a bit. The rust is being converted to an inert blackish substance. I don't know what the chemical reaction is but I guess it's reducing (de-oxidising) the rust.
7. The process deals with even the remotest corners of the tank. But once you turn off the current you must dry it asap. Mike recommends pouring out the solution (which is not particularly toxic – I dumped it on the gravel drive) and flushing with acetone to chase out the water. I used cellulose thinners (similar thing), then sat the tank in front of a fan heater for half an hour. Dry as a bone.

Did it work? See the before and after pic and judge for yourself. I think so. The orange, rusty smudge you can just see is only under the electrode, where very fine particles of brown sludge fall downwards. Otherwise the entire inside is grey or black.

Obviously it's less stress if you do the job before painting the outside, but the solution (which fizzes over sometimes when a big hydrogen bubble forms inside) is non corrosive on paint and chrome. Also, it helps to scoop out the scum and clean up the electrode (see pic) from time to time.

You can now seal the tank but I'm taking my chances as it is.

Monday, 18 January 2010

The joys (and otherwise) of pattern parts

Seeing as BSA shut down in 1973, it's amazing that you can still get virtually every part. Hardly any of it is original though, and the tinware generally comes from India.

You can get chromed tanks from the very useful Kidderminster Motorcycles (01562 66679), as well as headlamp brackets, mudguards and headlight shells. It ain't cheap: the original brackets I picked up at Stafford were £65 discounted, but I chose the wrong ones. The shorter replacements, for the earlier drop-yoke A50s, were £90 from the equally helpful Burton Bike Bits (

The catch is that this stuff only fits approximately. The chroming and polishing and overall quality is good, but one of the brackets was 7mm taller than the other. It needed shortening with Alan Seeley's disc cutter to fit between the top and bottom yoke. This then leaves a gap which rain and muck could get into, so I'll need to find some fat o-rings or use RTV to bung them up. The 'ears' are too wide for the 7in headlamp shell too, so I Araldited on a couple of washers to the inside to take up the clearance.

The biggest pain has been a new fork top nut. The threads are just too fat to screw into the new (or, for that matter, the old) fork tube. Mr Seeley's thread files and rat tail files have made no impression so far. I really need a lathe.

The picture shows Diplomat finishing off the installation of a new timing cover gasket last Sunday afternoon. What a fine fellow he is.

Tuesday, 5 January 2010

How to de-rust a tank

If I had a brain I would have looked inside the tank first and dealt with the light dusting of rust before applying the expensive paint to the outside. But no matter.

I went for a combination of mechanical and electrochemical treatment:

1. Chuck in some dried alpine grit, bung all holes with Blu Tac and wrap the tank tenderly
2. Tumble for 25 mins or so in a cement mixer (packed tightly with cardboard and polystyrene blocks)
3. Hoover out the gravel
4. Fill the tank with baking soda solution and electrolyse it using an old iron chisel as the anode, dangled in the solution. Electrical oomph provided by old mobile phone charger (c.500mA)
5. Flush, dry, add more gravel (washed this time) and shake it about
6. More hoovering and flushing, et voila.

I could have coated the inside of the tank with a sealer but the inside looked pretty good so I didn't bother.