Finally have the paint job done. I used synthetic Khaki No 3 sourced from Auto Paint St Helens. I asked for Satin finish and purchased 1 litre in a tin, 4 aerosols and a litre of paint thinners. which have done the job. I will post pics when all is finished. Starting to re wire this week. Is it vital to use lots of different thickness's of wire? Fewer the better! Which wires require which thicknesses? I have printed out the wiring diagram. I think someone has already rewired some of it so want to do the lot as there is still some old stuff where the rubber has perished.

email (option): araine11@hotmail.com

Hi Arthur,i see you arn't getting much help with your wiring question,there is another post regarding wiring,you mat be able to get your heads together.
The wire is available from a firm in Tottington Lancs that i posted here a while
since,i don't have their details to hand right now but can dig them out if need be
good luck
cheers Rick

email (option): richardholt@rocketmail.com

Hi Arthur,

Here are the details,

Electrical Engineering Services
301 Turton Road
Tottington
Bury BL8 3QE
England

Telephone: 01204-884383
Email: EESclassicwiring@aol.com

I called in there in June, the guys name is John. He showed me around, he does in in a large garage type building. Arthur I am in the same boat as you, Steve gave me a few tips, but still not sure what gauge wire I need.
Dave

email (option): jeepfinger@blueyonder.co.uk

Hi Arthur
Im not to the wiring stage yet but looking at some of the original wire on my bike the heaver wire is 26 strands of 0.0125 inch which gives about 2 mm sq and the thinner 16 strands which gives 1.26 mm sq. these are about 14 and 16 American Wire Gauge. The heaver wire was to F, A, & D on regulator the thinner on E. The thicker also to ammeter – most of the rest of the wiring was not original. Watch out a lot of auto cable is measured by the outside diameter across the insulation or across the wire not the cross section area which is the important measure and they rarely quote the acceptable volt drop for the current ratings which can be higher in 12 and 24 V systems. There is a rule of thumb for auto wiring which gives the cross section but you need to know the acceptable volt drop round the circuit. The formula is

Cable cross section in mmSq = 18 x circuit length x Amps divided by Acceptable V drop x 1000
for example for a 2 metre circuit (from gene to headlamp and back to gene via switch and dip switch) drawing 6 amps (36 watt head lamp) guessed acceptable V drop 0.1V gives:

18 x 2 x 6 divide by 0.1 x 1000 = 2.1 mm square cross section wire

If you want to put a fuse in it is there to protect the wire/battery/generator from a short circuit so a 10 amp fuse should do but dont run the horn through it. Also as I think Ian Wright mentioned its a good idea to run earth wires back to a central point so the earth return current does not have to go through bearings and painted joints.

The headlamp, horn, and charging circuits are higher current, speedo, tail, pilot lights are lower current.
Regards
Doug W

email (option): watsond@xnet.co.nz

Not that easy to understand. I have a chap coming around Friday night to supervise me replacing mag oil seal and re timing the ign.(my 1st time) He rebuilt his M20 about 10 years ago so will consult with him. I know that wire is measured in amps it carries and that the main power runs through cables to and from battery, ammeter and regulator. But as this electric power is only used for 6V lights and horn is it critical what wiring is used?

email (option): araine11@hotmail.com

Hi Arthur,

Not too sure about that, but why don't you give John a call. He just doesn't sell wire, he make wiring looms as well, but not for BSA M20's.

Dave

email (option): jeepfinger@blueyonder.co.uk

Like to just say that to light up a bulb of a certain wattage at the end of a length of wire a 6v system needs to carry twice as much amps as a 12v would to do the job.
so this post is for others (like me) who aren't that up on electrics can at least get a rough idea of the kind of thickness of wire needed for any given circuit on their 6v bike by looking at a later 12v bikes factory looms wires & accepting that they are only half the core thickness needed for your 6v ... obviously 12v bikes often don't have many areas of direct comparison but i think it was worth the risk of me mentioning it here even if its obvious to most.
So just to make the over simplified statement i came here to do.... 6V wiring needs twice the core size of 12v wiring : )

Cycle Fred,
You are correct about the thicker wire for the 6V system, the Lucas dynamo MRC2 wireing is easy to do if you have done it a few times. No need to buy a loom just make one to fit the bike. Arthur where are you in the UK gather your up North, i am in Huddersfield, i can send you a sample of the wire i use for a 6V Lucas system if you want.
Tim W

email (option): t.j.walker@btinternet.com

Hi Tim,

Cycle Fred might not be up north, but I am. I live in Keighley, not too far from you. I bought my M20 from Kirk Burton, but it was 24 years ago. Might be interested in a sample of wire.

Dave

email (option): jeepfinger@blueyonder.co.uk

Dave,

Mail me direct if you want a chat about it.

Tim W

email (option): t.j.walker@btinternet.com

According to maintenance manual (Air Pub. 1657B) the maximum voltage at the regulator can vary between 7.7 and 8.3 volts. Of course, the nominal system voltage is 6v, so the variation is quite large. Limiting voltage drop to 0.1 volts seems 'way too restrictive. Maximum output of the long dynamo is 60 watts, i.e., 10 amps at 6 volts (or less at higher voltage). AWG 18 or metric no. 1 wire (1 mm.) should be plenty and, since it is easier to source no. 2 or 2.5 wire, the most common wire gauge would be plenty even for the wires carrying the heaviest loads. BTW, in a direct current system, like a vehicle, the only function of stranded wire is that it is easier to bend and follow curves than solid wire. In alternating current systems, especially of higher frequency, stranded wire carries higher amperage than solid wire of the same cross-section because AC is carried close to the surface of the strand and the higher the frequency the more closely to the surface is the current "squeezed", so at higher frequencies you want to have more strands even if they add up to the same aggregate cross-section.

email (option): jonny.rudge@verizon.net