Hi all

I've gone to check my 1940 m20 over this morning to find that the lights won't work at all. Bike starts and runs well, battery is fully charged but no head or tail lights. The third terminal of the t switch gets power but when I turn the switch to lights on the third terminal drops to 0.1v. Is the problem likely to be the switch ? Are they items that are meant to be cleaned / serviced ? Any help or suggestions about how to diagnose the problem appreciated. Cheers Ant

email (option): Antkenmare@gmail.com

Hello Ant.

It sounds like a poor grounding/earthing somewhere.

I would start with the battery terminals, the earthing to the chassis,
The wires continuity.

The switch does need cleaning sometimes,
But usually you can get it to work if you wiggle the knob a bit...

Another option, is that the battery is actually flat.
If you measure the voltage across the battery with no load,
Sometimes the difference between a fully charges battery and a flat one
Can be only few milliVolts.
You can check that by either test if you do have lights when reving the engine,
So you would have the dynamo to light up the bulbs,
Or connect a bulb directly to the battery and see if it light up.
(You can also measure the batt voltage before connecting the bulb,
and then connect the bulb, and see if the voltage drops.
If it does, than the problem is with the batt.
It can be sometimes be saved by adding distilled water to a dry cell,
Or the battery is gone...)


Cheers,
Noam.

email (option): noam10@gmail.com

Hi there

Many thanks for your reply, I have no lights even with the bike running and battery seems quite fresh.

Is the earth to the frame at the regulator or is it under the tank ? Bit embarrassed I don't know 😊

Ant

email (option): Antkenmare@gmail.com

Hi dear Ant.
Happy to help!

The "earth" (Can be positive or negative, depending on your system)
Is one of the battery poles, which is connected to the chassis.

It can be under the tank, or anywhere else, after 77 years...
Does not really matters, as long as it's sound.
At the same time, I would take the chance to generally check all of the main electrical connections.
It only takes minutes and can solve your issue.
The horn has a "permanent"(+) (For a negative ground system)
And it gets the (-) trough the chassis when in use.
[The other way round for a positive chassis system]
Does the horn work?


Please let me know should you need any further info.

Good luck,
Noam.

email (option): noam10@gmail.com

Well I was sure the battery was fine but after replacing it with a new fully charged one (and sorting a earth issue) hey presto I have lights ☺

Problem is I think it has highlighted that the dyno isn't charging as the lights don't get brighter with the engine being reved.

I've just being reading the tec section on dynos and will run through it all at the weekend. Any other tips on dynos ? Don't quite understand this flashing milarki. I understand, I think, that the dynos can loose there magnetic field and think that flashing 're energised it ? Is that right ?

Ant

You're going to have to come to terms with some electrickery or it's going to be an unhappy relationship !

This site is quite good :-

http://matchlessclueless.com/electrical/lucas/

A fully charged battery may well mean that brightness does not increase perceptibly with revs.

Rik
Assuming your bike has an ammeter,switch the lights on with the engine stopped and note the ammeter needle position. It should be showing a discharge.Start the engine and rev it up gently,the ammeter needle should move towards a charge if the dynamo is working.Depending on how good it is may even move the needle to the charge side. My WM20 and my Matchless(same system)shows a small charge under these conditions.
The test will not tell you how efficient the dynamo is but if there is no sign of a charge it gives you a starting point. The Matchless site mentioned before is a good place to start if you need to go into more diagnostics.
Hope this helps
John

If you are not sure of the polarity of the dynamo. Take the field wire and flash it against the live terminal of the battery this will ensure the dynamo is correctly polarised. If you want to see if dynamo is producing electricity, insert wires into the terminals on dynamo join free ends together hold on the side of a 12 volt bulb and touch base onto a metal part of bike. On revving engine bulb should light. Use 12 volt bulb as dynamo can produce 20 volt if revved to high

Thanks guys - learning fast !!

Have studied that web site and tested the dyn o it works great. Problem is the regulator - no action at all !

Can they be reconditioned ? Or do most m20 owners swap out the coils for a modern solid state item ?

Thanks again - your guidance has been invaluable !

Ant

If you are going to fit a mechanical regulator don't use an Indian one. Best thing to do is buy an electronic regulator and fit inside old one after gutting it. Can recommend Dynamo Regulators Ltd. www.dynamoregulators.com.

I can recommend Dave Lindsley. His solid state regulators are built to [modern] army spec standard. If you buy one of the cheaper far east made ones that fit inside the regulator body he says to cut away the fibre base and mount directly on the steel chassis in order to keep it cool. My cheapo Paul Goff item now has a thick ally base added with heat absorbant paint on the interface: all to help dissapate heat. I had a fibreglass battery from Paul to replace the same make that wasn't working. Although I wrapped it in rubber foam it lasted a month or so, so I went and bought a trad lead acid, which has been fine.
I've got a couple of MCR2s that have been tested and are worth setting up, but as far as I know the 2nd world war regulator was different

email (option): j@clogmaker.co.uk