Rotor opened up

[mrclubike]

Went to start up the bike after  adjusting the valves and noticed the volt meter was stuck at 12 volts
turned it off and turned it back on and the gen light is not on
check rotor resistance and it is OPEN
I ordered  a new rotor and it is on its way from Motoworks
By the way Could not get the Motobins site to work 

So I wanted to know more about what happened and if I could rewind it 
Tried to pull the back claw off and it would not budge at all
Not going to dissemble  it with out damage  so out comes the grinder
Just in case some one else wants a go at getting her
apart
Here is what it looks like under the claw

[Justin B.]

I have had a replacement on my '81 R100 for about 12-13 years now, no problem  I got it from Euro MotoElectric.

Seems I remember that a puller is not the correct way to get the rotor off.  You use either a special "bolt" or a bolt and piece (1/2" long, maybe?) of something fairly hard that will slip into the hole, tighten in the bolt, and the rotor will pop off.

[georgesgiralt]

Now, it is open ;-)
Have you heated it before pulling the jaws ?
I think the interference is quite severe here.
IMHO rewinding it was not an option, given the quite low price one can find decent second hand one these days. And you have to find a guy having the skills, machinery and willing to do so ....

[mrclubike]

I have had a replacement on my '81 R100 for about 12-13 years now, no problem  I got it from Euro MotoElectric.

Seems I remember that a puller is not the correct way to get the rotor off.  You use either a special "bolt" or a bolt and piece (1/2" long, maybe?) of something fairly hard that will slip into the hole, tighten in the bolt, and the rotor will pop off.

I am not talking about getting it off of the crankshaft
I have the special stepped puller bolt for that and it come off the crank with out a hitch
I am talking about disassembling the rotor itself for rebuild or repair 

[mrclubike]

Now, it is open ;-)
Have you heated it before pulling the jaws ?
I think the interference is quite severe here.
IMHO rewinding it was not an option, given the quite low price one can find decent second hand one these days. And you have to find a guy having the skills, machinery and willing to do so ....

I tried just pull it cold first and then tried some heat and it would even begin to come off
That thing was VERY TIGHT 

You are correct rebuilding it is not a do it yourself option for sure 
And probably not economical to have it rebuilt by a auto electric rebuilder  either

I was able to find the failure point
The wire failed where it passed thru the claw 

[mrclubike]

What was strange is I just got back from a 1100 mile trip and I am fairly sure I had charging all the way home

It must have separated on the cool down cycle

[Bob_Roller]

I always wondered how cost efficient it was to rebuild a rotor .

The BMW motorcycle parts site that I have done business with the last 20 years, stated that you needed to send in your failed rotor, or stator, before they would send a replacement .

I just checked the site today and that verbage is no longer on their site .

I have have heard for over 30 years, that the rotor was  highly prone to failure .

With the three R65's and the '87 Guzzi , same Bosch charging system on the Guzzi, the bikes have accumulated 300,000 miles, 492,000 km on the original factory charging system parts .

Only parts I've replaced, are alternator brushes on the '81 R65 .

[Tony Smith]

Bosch alternators fail in exactly the same way. As recently as a month ago the alternator in the Kombi died - my immediate response was to order a brand new one and then I looked at the old one - the break was in a relatively accessible place so I soldered it and then soaked the rotor in insulating epoxy.

When the new one arrived I didn't like the look of it at all, no brand and no country of origin (which generally means China or India). I put the repaired 40 year old alternator back in and have kept the un-named new one as a spare.

[Tony Smith]

Here is what it looks like under the claw

To get these buggers apart, given that you will not be reusing the wiring, the accepted method is to warm them up to a nice cherry red with a blowlamp - they generally come apart easily then. But as you rightly point out the time to make a jig to rewind etc means that it is a whole lot more efficient to just buy a new one (of decent provenance).