Generator warning light came on at high revs

[BSA Bob]

Today I let my R26 rev out in 3rd gear uphill. At slightly over 80kph the generator warning light came on. I backed off, the light stayed on for about 20 seconds & then went out. Everything's working OK since.
Does anyone have an idea of what this could be? I haven't a clue.
The bike has an original setup, original generator & mechanical regulator.

[BSA Bob]

[CowBoy]

It could be that the armature isn't running quite right. Then the carbon brushes jump and the red lamp comes on.

[strichzwojan]

Cheap and easy: clean the grooves of the collector on the alternator with a wooden toothpick. Have a look at the brushes. Worn out? Springs tension is OK? No wires loose? Are the brushes easy to move in their guidings?

[BSA Bob]

Thanks for the replies.
I thought about the brushes jumping but figured the length of time the light was on (well after I backed right off) meant it wasn't that. Anyways I had a good look today & can't find anything- the copper faces are clean with no dirt between them, no loose wires & the brushes look OK.
I'll wait to see if it happens again.

[patro]

I'm not quite sure if it's the same with R26.

But with my R25/2 every now and then I had this issue with the ignition nail. I don't know the right translation to English language. Especially in a rough environment it happens that the nail is jumping out and the contact is disconnected.

So you could try it with a bungee wrapped around the lamp to fix it.

Meanwhile I repaired ignition platine by bending the contacts.

Motorradmechaniker i. A.

[Borgward]

In this case, the ignition would also be interrupted but obviously only the charging indicator light came on

Hubi

[4Taktix]

Armature/collector out of round is plausible for the symptom. ( jumping brushes )
Also bad ground/earth connection(s) were possible.
I had similar issues a few times now, getting worse until the generator light didn't come off again at all
and the battery was completely discharged.
The collector looked perfect, like from a book how it schould look.
Nevertheless Timmäh gave me the advice to carefully grind it with 400 Grit Paper.
We were on a trip and far from home, so we had to come up with a solution right there, right now.
We removed the sparkplug and generator lid.
One guy pushing the sanding paper to the collector, another one turning the engine over by Kicker a few times.
Afterwards we cleaned up the collector with a fuel-soaked, clean rag.
That did the job ! Battery was charged again and we reached home without further issues.
Long termed solution was trueing the collector on a lathe and install new brushes.
Since then the issue didn't occur again.

[BSA Bob]

Hi folks, thanks again.
Patro, as Borgward says there was no interruption to the ignition when this happened & my ignition lock's in good condition. Your English is better than my German.
4Taktix, I'll recheck the wiring for loose connections but I'm pretty sure it's OK.
When this happened I was revving the bike a bit harder than usual, I don't go over 80 in 3rd & rarely at that. I don't thrash the bike, if I want to go faster I can get something else.