Replacement of Brigitta's Failed Rotor

I had mentioned in my previous post, that Brigitta my '87 R80 BMW Airhead had developed charging issues. 

Diagnosis had led to planning a replacement of a failed rotor that was not passing the continuity test.

Dick Paschen is the Colorado AirMarshal for the Airheads Beemer club (ABC).  He told me that he had a spare rotor and was willing to help me install it today.  

So I showed up at his home and he even fed me breakfast before we started work on the motorcycle! 

Dick patiently guided me through the whole process beginning with removing the front cover after disconnecting the battery in negative cable and disassembly of the alternator.

It's very important, to disconnect the battery, otherwise you may cause an electric arc while removing the front cover and burn out your diode board! 

Here's the alternator, wires disconnected.  A couple of the black plastic insulator bits broke as we removed the wire connections on the alternator. We would use some shrink tubing at the end to fix that.

Here the stator has been removed exposing the rotor.  The shiny bolt in the center is a special tool to help pull the rotor out of the alternator.  

Note the large screwdriver jamming the rotor in place preventing it from turning as we worked to loosen and later tighten the rotor.  Simply putting the transmission in gear did not do the trick, probably a harbinger of clutch pad work sometime in the future. 

I had only observed the brushes, shown below while mounted. It was one of the things that RichardM suspected.  However, the fact that the rotor was failing the continuity test bypassed that thinking until today. 

Once the stator was pulled off I was able to observe easily into the rectangular wells that house the brushes and they were very worn down!  

Luckily, Dick had a spare set of brushes!

Below you can see one of the old brushes lying on top of the brush housing to illustrate how worn down it had become. 

The new brush is flush with the end of the housing. 

Note: the old brushes were soldered on, so Dick cut off the wires and we just used the new brushes' connectors to secure them onto the 8mm nuts that secure the brush assembly.

It was a bit fiddly, working to put the brushes in while holding the springs out of the way but we got it done.

Fully assembled, awaiting heat shrink tubing.  

Before we put the front cover back on, Dick had me reconnect the battery negative wire and we did a quick test.  The generator light came on as expected and desired, and the bike fired up right away, and the volt meter showed she was charging up!  Success!

Quickly disconnecting the battery again, I put the front cover back on with Dick's help and we rolled the bikes out onto the street. 

Brigitta back home

My thanks to Dick Paschen, Colorado AirMarshal for his time, patient training, and of course the spare rotor and brushes!

Here's the broken rotor: