Dynamo not charging

[bevanclark]

Hi folks,
The E3LM dynamo on my 1950 VB is not charging. I have video evidence that it was charging before it was shipped from the U.K. to me here in N.Z..

The bike is positive earth; the resistance between the dynamo body and a frame bolt is 0.2 Ohms, which is the same as I get when I short the leads of my multimeter together, so i think the earthing is o.k..

I have followed troubleshooting guidance given on the "matchless clueless" website and have made the following measurements:
- Field terminal to earth resistance = 3 Ohms; Dynamo terminal to earth resistance = 4.3 Ohms
- With the F and D terminals shorted together and the engine idling, I measure around 0.2 V between the terminals and earth, which doesn't seem to change much if I increase the engine speed a bit.
- I have tried flashing the field coil, but no change in voltage readings.
- I have removed the brushes and lightly cleaned the commutator (it wasn't particularly dirty). To my inexperienced eye, the brushes and commutator appear o.k.

A Lucas manual I downloaded seems to suggest the trouble is with the field winding, but the resistance I have measured is the same as that on my Panther's E3LM dynamo, and it works perfectly.

I'm not sure what the next troubleshooting step should be.

Any guidance would be much appreciated.
Cheers,
Bevan

[alan.moore]

Bevan,
have you removed the two field wires from their terminals and then tested the resistance of the field coil using those two wires?

[will_curry]

Bevan,

My next step would be to try motoring the dynamo. See John Nash's excellent post
on the subject of testing dynamos here:

viewtopic.php?f=8&t=189

Will.

[bevanclark]

Thanks for the replies folks,
I measured the resistance between the field terminal and earth, but will check between the wires as you suggest.
Dumb question, I know, but can I remove the dynamo while leaving the magneto in place ? I've only ever removed the entire magdyno as a unit on my Panther.

Further investigation will need to wait until after the Xmas madness is over.
Best wishes for the season,
Bevan

[alan.moore]

Yes you just need to remove the dynamo strap and the one long nut on the timing side of the triangular cover

[nevhunter]

Just loosen the strap. By one screw is enough. A few turns of the easy to get at one. Tighten it up though later. I've seen a couple go down the road and it doesn't improve them .Nev

[bevanclark]

Hi guys,
Just a followup in case anyone is interested. It was such a lovely day here (29 C), I decided to take the VB for a bit of a ride before pulling the dynamo off. When I returned, to my surprise, it was charging when I revved the engine a bit above idle. Not sure why, since I had tried flashing it etc previously without success, but it now appears to be working fine. Even the old cvc unit is clicking in and out in what appears to be a correct manner.
Long may it continue,
Cheers & Happy New year
Bevan

[simon.holyfield]

Loss of magnetism maybe?

Anyhow it's working and you can ride it. Congratulations and happy new year!

[paul.jameson]

With those symptoms, my money is on sticking brushes. I will guess that the brushes fitted have a blue woven insulation as opposed to a yellow helical one. If so, they do tend to stick - so remove them, wipe them over with a rag, push the rag into the brush holder to remove carbon dust from there and re-fit the brush. That should solve the problem for a year or two, at which point you may need to repeat the process.

[bevanclark]

Thanks gentlemen. Will do as you suggest Paul.

Obviously, its not a fast bike, but it sure is fun to ride; and what a wonderful sound
Only disconcerting thing is that the seat springs look correct and in good order, but seem too weak - I'm not a big bloke, so don't compress them much i guess, but I get the feeling that my bum is waving from side to side (so to speak !).
Cheers,
Bevan