My R65 stops charging after 3.500 RPM

[Dustit]

  New 20A  AGM Battery
  New Voltage Regulator Wehrle Part Number 12321244773
  New Diode Board
  Cleaned every connection that I could find and used Dielectric grease.
  Remove and inspected rotor brushes and verified tension against the
  rotor . all looks good.
    Removed starter connections cleaned and greased.
   All was done after not being able to find a fault in testing before replacement . Gave in to the idea that perhaps problem developed with heating of the engine and components failed intermittently.  
    Installed this just few days ago , Battery Tender Quick Disconnect Plug With Lcd Voltage Display Monitor
      Charging drops just as RPM goes past 3.500 and will return as RPM slows again . Showing 13.6 volt before it drops out.
    I have come to the conclusion that at higher RPM the rotor has a contact problem the shows up as it spins faster .
    Need more ideas or more things to check .

[montmil]

Perhaps the rotor is failing. Not uncommon. If you have a shop manual, you'll find easy test steps. Also check Snowbum's website. It's something simple, most always.

[Bob_Roller]

Have you noticed if your 'GEN' light is acting unusual when the charging voltage goes down .

You may have to do this when it is dark out, sometimes it comes on faintly with charging system faults .

Here's an excerpt from Snowbum's BMW tech site .


   Rotors usually OPEN circuit, and a simple
 ohmmeter test across the slip rings will identify that.  An open rotor or brush will usually not
 allow the GEN lamp to light up.  A rotor can work (or sort-of) at low or high rpm, and then not at
 another rpm.  GEN lamp indications can be erratic with rpm too, signifying an opening and
 closing of the rotor internal connections. It is possible to use an ohmmeter on a rotor with the
 engine running over a range of rpm, with the rotor D- and Df connections disconnected, but
 there can be meter complications, so I suggest you NOT do that.

Kinda points to a rotor issue .

[mrclubike]

I would do what SB says not to
I would remove the front cover and run it with an ohmmeter across the brush leads (disconnected from the rest of the wiring of course) and see if the the rotor circuit is opening under high RPMs.
Another test would be to full field the rotor with an amp meter hooked to the rotor and see if the amp draw goes down then  you know the resistance is going up with increase in engine RPM.
I like to test thing under load  

[georgesgiralt]

IMHO, your rotor has a failed wire which cuts open when the centrifugal force goes too high.
As the GEN lamp search it's grounding through the rotor wiring, it won't light.
Maybe you can see if the wires going from the coil to the copper slips are showing and mechanically sound  or properly soldered ?
The only way to be sure is to borrow another known good rotor and try it.

[Dustit]

 I was able to get a second person to help me and tested a few more things . The rotor is going open for sure , took more run time to build heat with the front cover off . I have rotor arriving today , sure hope  that finishes the repair on the charging system. The alt. light would come on as charging started to drop off and then go out as the rotor failed completely , I had not noticed that when I was riding it .
   Will post my results after the new rotor install. Thanks for the help.

[Dustit]

  New rotor installed now and around 200 miles of riding , looks good to go. Max charging went from 13.6 up to 13.9 . I did see voltage drop back to 12.8 when RPM went past 6,000 RPM . I did not install the new brushes I have yet and am wondering if the brushes may start to float at the higher RPM . My brushes are shorter than new and maybe the spring tension is not as good as it was 35 years ago.  

[montmil]

Measure the length of your existing brushes. There's a minimum length -and I do not have that info handy- so check in with Da Bum.

What happens with worn brushes is the 'snail' spring eventually makes contact with the brush holder body and the spring tension holding the brush in contact... Goes away. The roadside fix involves whittling a small bit of wood to place on top of the brush, then put the spring back on top of the lumber. Contact pressure returns and you're underway for the ride home.