Replacing the alternator "monkey nutz"

[frankenduck]

If your K bike has a few miles on it and is starting to make noise near the right rear of the engine then a common cause of this is that the rubber bushings (a.k.a. monkey nuts) in the alternator driving cup are worn.  Replacing those should make the problem go away.

The part number is 12311464877 for both the 32A and 50A alternators. You'll need three of them.

To replace them:

1 - Remove the side covers.

2 - Remove the seat.

3 - Remove the L-Jetronic or Motronic.

4 - Remove the battery.

5 - Remove the alternator cover. (The triangular slotted piece of plastic piece above the transmission fill plug.)

6 - Remove the three 6mm Allen head cap bolts that mount the alternator.  These are often hard to break initially as corrosion is likely to have built up in the threads.  Sometimes it's easiest to get good leverage on the lower left mounting bolt by removing the coils and starter motor.

7 - Pull the alternator off and replace the monkey nutz.

8 - Put everything back together.  Lubricate the slots in the monkey nutz that go over the driving dog vanes with Armor All or whatever to make it easier to get the alternator back on.

[Scott_]

I'll also add from personal experience, just a "little dab", and I mean as little as possible of some RTV gasket sealer(or other "sticky" substance) to "hold" the "nuts" inside the alternator drive cup while you are trying to assemble it.
I used some of the Black RTV, as that's what I had on hand.
And as Duck mentioned some armor all or "slippery" agent inside the "crack" of the nuts to let them slip onto the drive teeth.

[RobP]

I'll also add from personal experience, just a "little dab", and I mean as little as possible of some RTV gasket sealer(or other "sticky" substance) to "hold" the "nuts" inside the alternator drive cup while you are trying to assemble it.
I used some of the Black RTV, as that's what I had on hand.
And as Duck mentioned some armor all or "slippery" agent inside the "crack" of the nuts to let them slip onto the drive teeth.

This might be a good application for 3M Silicone Paste.   I've been using this stuff lately when assembling many rubber parts such as O-rings and grommets.  Provides a good lubricant for fitting rubber parts, and is good for the rubber.  Also good for lubricating the rubber grommets on the battery and side covers to ease installation and removal.

[K75rt]

I've done this a couple times, never had a problem keeping the OEM ones to stay put - make sure to thoroughly clean the cup and let it dry.  I thought about ArmorAll to help slide on but frankly the "ArmorAll vs Vinylex" debates over on the BMW cage boards scared me off of it (fwiw the Vinylex universally won by a mile in real world tests).

So I used a completely organic compound with no silicone, no petro distillates, etc.  I used a little saliva on each slot - cheap and worked like a charm :)

[beemrdon]

Hey there Y'all,

I own a 1996 K1100 LT with 70,xxx miles,  (my avatar) so I'm curious as to what bad monkey nutz sound like? (Seems like that motor makes a lot of various sounds)
Can you hear them easily enough if bad?
Do you hear them at idle or at speed, or both?
When the engine is cold, hot...or both?
Any other things I should be paying attention to at this mileage?

Thanx,
Don

[The Mighty Gryphon]

When reinstalling the alternator use a pair of headless 8mm bolts about 3" long to help align things.  It will save you at least 15 minutes and a boatload of cursing getting those damn monkey knutz onto the drive dog.  The bolts that you use to align the transmission will work.  That's what I used.

I just did a rear seal replacement on my K100RS and as part of the job checked the knutz in the alternator clutch.  Re-installation was a b!tch and after about a half hour I noticed that the bolts I used to align the transmission might help.  Put them in and the alternator went in on the first try.  It went so easy that I thought the knutz may have fallen out of the clutch so I pulled it out to check.  Second time it went in just as easy as the first.

One other tip:  When you make those guide bolts, just don't saw the heads off.  If you file a chamfer on the end it will make sliding the transmission  and the alternator onto the bolts a lot easier. 

[BigRedBrick]

This has to be one of the best tips I've ever run across.  Just had my alternator out and back in to check the "nutz" and it went back so slick I could hardly believe it.  Kudos to you Gryphon.  Well done.  Oh, and I might mention sawing a small slot into the cut off shaft end for a thin bladed screwdriver.  Helped get them back out.

[BoardOfCan]

How easily did you get it out & back in? Did you feel compelled to remove the ABS?

[BigRedBrick]

I had recently removed my ABS system as it refused to work despite many many resets and much cursing.  I do agree that it is a worthwhile safety device (when it works) so removing it was regretable but all my previous bikes had "normal" brakes and I am quite used to them.  Having it gone did make pulling the battery tray and then the alternator both possible and a real breeze.  Using the two guide bolts is well worth doing. The alternator slipped right back in with little problem.  Also, I noticed that the nutz holder "cup" has a referance mark on the outside that alignes with the split in the "nutz" so that you can visually line it up with the blade on the reciever.  That helps too.  Between that and the guide bolts it was a piece of cake.

[BoardOfCan]

I have to have another go at it this weekend - getting the 3rd "interior" bolt off (between the alternator and starter) wasnt working with what I had available, I started to think I was going to need to get the ABS off & out of the way. And I'm not excited about that. Mine still works great, I'd want to reinstall it after. I'll definitely make some headless guide bolts - they go on the outer 2 holes?

[BigRedBrick]

Unfortunatly they best go on the two lower bolts in my opinion.  From what I read you might start with just pulling the upper solid brake line from the ABS unit. That might give you some room to get the alternator out without pulling the ABS entirely. Getting to the lower inner bolt is a PTA with the ABS in there in any case.  BMW says to just pull out the ABS to get to the alternator (Thanks alot, Guys!) Wrestle off the negative battery strap. That might help get you to that bolt.  If it is any consolation, bleeding the ABS lines isn't really that hard but have some vacuum caps ready for weepage if you disconnect the lines.  Good luck.

[BoardOfCan]

Only a bummer because I fully rebuilt and bled my brakes when I first got the bike. Feh! It's good practice and my brakes are gonna be razor sharp when I'm done! Either way, thanks so much for the advice!!!

[RobP]

Also, I noticed that the nutz holder "cup" has a referance mark on the outside that alignes with the split in the "nutz" so that you can visually line it up with the blade on the reciever.  That helps too.

Hmm, somehow I missed the reference mark, but I did make my own marks on the outside of the cup with a Sharpie marker to show the alignment points, and that certainly helped.

[BigRedBrick]

It could be that not all drive cups have the marks. You seem to have an 85, Rob, whereas my ride is a 96 so maybe it was added later on. At any rate, it is a good idea to make one if it doesn't.