R26 not charging

[BSA Bob]

My R26 suddenly stopped charging with the red light on. It had briefly stopped charging when revved hard on a ride but came good, the other morning it wouldn't charge when I started it.
I'm not confident to diagnose the problem, the manuals are vague about what the issue might be.
It has a standard generator & ignition set.
I've removed & cleaned the brushes & cleaned the commutator, they look OK & I can't find any wiring faults.
I connected a voltmeter between terminal 61 on the generator & ground. No reading. The engine stopped when the battery negative lead was disconnected.
The battery's good, measuring about 6.3 volts. No difference in reading across the terminals with the engine running.
I've cleaned the voltage regulator. I noticed that there are no gaps between the 2 contacts "b" in fig 212 of the German language repair instructions manual on this site.
And lastly, is there a diagram of the electrical connections in the generator unit itself? 

[BSA Bob]

[Heiko]

Here it is:

https://cms.bmw-einzylinder.de/index.php/literatur/anleitungen-und-abhandlungen.html?id=99

[BSA Bob]

Thanks for that, Heiko.
Do I infer from another post that you work on steam locomotives? Wonderful machines, I can talk about them all day.

Unfortunately I still can't get an idea of what the R26 fault is.
I've checked & cleaned the brushes & commutator again. Using a meter there's current flowing between the commutator & terminals- ground, 15 & 61.
I bridged the terminals 51 & 61, this blew a fuse on the + side of the battery.

Does this give any clue as to what might be wrong, alternator or regulator?

[BSA Bob]

As per the piece Heiko sent, I tried to repolarise the alternator.
I connected a wire from the + side of the battery to terminal 61 with the ignition off, & with the engine idling.
The regulator immediately started smoking at points "b" I mentioned in my first post.
The 15 amp fuse on the + side of the battery didn't blow.

[Heiko]

Thanks for that, Heiko.
Do I infer from another post that you work on steam locomotives? Wonderful machines, I can talk about them all day.

Thank god, no!  I am an authorized expert for rail vehicles and railway operations manager.

[Dieter57]

And for this to Heiko ?

[BSA Bob]

First, apologies for what are probably some meaningless readings, I'm not confident with electrics & have been cautious.
Anyway, I think I've isolated this to the regulator.
All the contacts of the reverse current switch are engaged at once, no clearance between them.
If the outer contacts are separated by a piece of paper the bike charges at about 7v across the battery terminals.
Does this seem like a bad fault (closed contacts) or would there be a chance of adjusting it?
I'd get a professional do do this, I'd just like opinions from here before I start anything.

[Heiko]

Hi Bob,

you can adjust them but do not know this at the moment. To long ago. Think Eppo has described it last year.

[rolf]

there must be a clearance when the engine do not work...otherwise the whole batterie amperes flows into the dynamo.
When I read this....I think you use a Bosch F regulator?
If yes.....grummel a few words and buried him....he is too old

[BSA Bob]

Thanks for the replies.
Heiko- I'll try to find the post you mention, but it seems best to buy another. And what's wrong with steam locomotives anyway?
Rolf, it is the f regulator that's fitted, probably the original for the bike.
So an electronic regulator has been ordered.

[Heiko]

And what's wrong with steam locomotives anyway?

Interesting to look at, but when you work on it, everything gets heavy and dirty. Visibility isn't adequate when driving.

[BSA Bob]

Wonderful machines whose time has passed.

[rolf]

like us

[Eppo]

The brother of my grandfather worked as an engineer on steam lokomotives, maintaining, restauration and regular testing of steam boiler components.
As a child I was always faszinated when he comes over and talked about his job. Too bad he passes away too early 😢.

[BSA Bob]

The electronic regulator's arrived. Just asking here to confirm,
The instructions mention isolating the connection from the exciter field coil. Looking at the bike from the front I think this is the wire at about 10.30 on the clock face, near the exit for the HT lead?
And the field coils wire is yellow & about 7.30?
Assistance appreciated.

[Borgward]

to be on the safe side check the cable: the resistor cable is single wire, the field coils are litz wire.

Hubi

[BSA Bob]

Thanks for that.
I had some trouble tinning the litz wire. Up & running now.