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Alternator Drive Damper Replacement

Changing Alternator Drive Bushings on a K75

By Ted Verrill

(Editor’s Note: See below for K100 article)

Parts You Will Need:

3 Alternator Bushing Sets, Part # 12-31-1-460-306 (~$9.00)

Parts You MAY Need and Should Probably Have:

1 Alternator Drive Clutch Part # 12-31-1-460-302 (~$8.00)
1 16 mm Spring Washer Part # 07-11-9-933-155 (~$0.70)

Tools/Things You Should Have:

1 Tube Dielectric Grease
1 Lubricator s/a Armor All
1 tube Red Loctite

For the Battery Tray and Mounts:

4 Battery Mounts, Part # 61211233028 (~$1.20 Each)
4 6mm Wave Washers (~$0.15 Each)
4 6mm Nuts (~$0.15 Each)
1 Krylon Spray Paint Black (~$3.50)


Part I: Disassembly

Put the bike on the center stand.
Remove the seat.
Whenever I do a job like this I use a clear plastic multi-compartment box to keep all of the screws and circlips both separate and in one place. Try Wal-Mart, around $3.00.
Remove the alternator shield (2 hex bolts)
Remove the computer and the housing.
Remove the coolant overflow tank.
Carefully examine your overflow tube at the overflow tank connection, mine was so dry-rotted it almost broke in half!
Remove the battery.
Check your water levels while the battery is so accessible!
Remove the battery tray (and mounts if have decided to replace them.)
Disconnect the alternator electrical connection.

Then, Remove the three 6mm allen bolts that hold the alternator.
An Allen extension is quite handy on the top and especially the bottom bolts.
Optional: Remove the battery tray. Remember that removing the battery tray makes removing and replacing the bottom bolt much easier, plus yours probably needs new nuts, bolts, mounts and a good repaint like mine did. Brush down the battery tray with a wire brush to remove old paint and oxidation. Wash it with a really good scrub-brush and a good cleaner (I used Simple Green), and thoroughly dry it. To paint the tray, hang it from a stretched-out coat hanger through one of the mounting holes and repaint it using newspaper behind/below to catch stray paint.
Carefully pull the Alternator slowly out, toward the back of the bike. Make sure to remove any bits and pieces of the alternator clutch or old bushings that fall out.

Part II: Examination

Remove and examine the bushings. If they are deteriorated, melted, or even missing you will have to very carefully examine the alternator clutch. You may even want to eat the $8.00 to be on the safe side and replace the Clutch anyway. Carefully examine the alternator clutch fins as well as the driven gear that engages the clutch (a flashlight helps here.) The Alternator Clutch Fins may have very fine hairline cracks, or may be bent, in either case you will have to replace this inexpensive part. If yours is fine and you don’t want to replace the alternator clutch, move on to Part IV.

Part III: Remove & Replace the Alternator Clutch

To remove and replace the clutch, insert an allen wrench through an angle-head box-end wrench and into the shaft. Hold the allen wrench steady whilst removing the nut with the box-end wrench. This is a little difficult and requires careful application of elbow grease. When the nut is off, remove and discard the spring washer and lift off the clutch. Watch carefully at this point for the Woodruff key. I have been told the key is not needed and in fact many K bikes don’t even have it. YMMV.

Position the Woodruff Key (if using it) and place the new Clutch onto the alternator. Place a new spring washer on the alternator shaft over the Clutch and use a little Red Loctite on the shaft threads before hand tightening the nut. Tighten to the correct Torque setting (I have no torque wrench so I just tightened it until I felt the spring washer had compressed, in other words “real tight”.)

Part IV: Replace Alternator Clutch Bushings, Remount Alternator.

Position the three alternator bushings in the alternator clutch and at each juncture where two bushing “pods” meet (where the alternator drive’s fins will engage) apply a small amount of lubricant (I used Armor-All and it worked quite well though I hear spit will do in a pinch.) On the outside of the alternator clutch you will see three marks, each at a spot where the alternator drive’s fins will insert into the alternator clutch bushings.

Here it really helps to have a partner on the other side of the bike to hold the alternator steady while you line up the clutch, and then hold the clutch steady and lined up while you gently push the alternator onto the drive.

First, line up the alternator so that it does not need to be rotated in order for the three mounting bolts to be replaced. Second, rotate the alternator clutch such that one of the three marks is lined up with one of the three drive fins (again, a flashlight is handy here…) Then simply slowly and gently push the alternator into position. You will feel a little resistance at first, but the alternator should evenly slide right onto the drive fins.

Repeat this procedure if necessary…

Tighten the mounting bolts to spec (again, “tight”) and clean, lube with dielectric grease, and reattach alternator electrical connections. Reassemble in reverse order (remembering to replace the battery mounts, and to clean and lube the battery connections with dielectric grease.)

PART V. Go For A Ride!

NOTE: You may want to inspect/replace the alternator brushes. It is simple, but not covered here…If you have had any charging problems, do it.

K-Bike Alternator Drive Rubbers

By Don Eilenberger
April 1996

Went and did the drive rubbers (we’ll call them goobers for clarity) on my K100RT last night – I think the results were what I hoped for, but won’t know until later today when I take it out on the road.

Approx time:

  • no lily gilding – maybe 1-1.5 hours
  • w/ lily gilding – about 3 hours

Special tools needed:

  1. Metric allen-drivers are good things to have, with 3/8″ drive and 2″ and 6″ extensions
  2. Normal metric sockets
  3. Normal metric allen wrenches
  4. Phillips and regular screwdriver
    In addition – for lily gilding, small stainless brush
    for cleaning aluminum surfaces, sandpaper (120 grit is good)

Parts needed:

  1. Rubber drive goobers (3 needed – cost ~$2/each/US
  2. Replacement nuts or washers for any you are likely to drop.
    In addition – for lily gilding, can of Wurth Silver
    wheel spray paint. Can of black glossy spray paint.

Step 1. Remove everything in the way of the alternator

  1. Remove battery side panels
  2. Disconnect ground lead from engine
  3. Take one end of seat holder-open off – so you can open the seat a bit further (lift off seats – this doesn’t apply)
  4. On right side of bike – remove pin holding computer in place.
  5. Slide computer towards left side – disconnect main connector (this is much easier than how the book tells you to do it – thanks to Corky Bessette for this tip).
  6. Remove computer
  7. Remove plastic housing computer is held in.
    *LILY GILDING – take housing to laundry room sink and
  8. Search for any of the four rubber thingies the housing sits in – they will travel to the same corner of the garage the little red tubes that come with spray cans like to hang out in.
  9. Remove battery holddown (two long phillips screws)
  10. Remove wires from positive side of battery
  11. Remove battery vent hose L fitting from battery
  12. Remove battery from frame
  13. Remove battery tray from frame (on early bikes, you must disconnect the rear brake reservoir from the battery tray – it can stay connected to the master cylinder). Four 10 mm nuts hold the tray in place
    *LILY GILDING: You can now clean up and paint the
    battery tray and the battery holddown.
  14. Move coolant overflow tank out of the way (you don’t need to disconnect or drain it – but try to keep it upright more or less)
  15. Remove plastic side cover over alternator – two allens
  16. Disconnect main connection from alternator – this plug pulls straight out towards the rear of the bike (it looks a bit confusing – ask me how I know!)
  17. Remove 3 large allen bolts holding alternator in position (one is more or less hidden between alternator and starter)
  18. Pull alternator towards rear of bike and remove from bike
  19. Remove old goobers
    *LILY GILDING – at this point, you can clean everything
    in sight. I’d resist painting the alternator, but a good
    cleaning with a stiff brush is in order. Do not allow
    dirt or metal particles to get inside – this would be
    a bad thing. Also a good time to check your brush length..
    two screws on white part with transistor on it. See
    books for acceptable lengths (this part is a common
    Bosch part – used on all newer bosch alternators – it
    can be purchased from sources other than BMW moto dealers)
  20. Lightly grease new goobers (I used silicon vacuum grease – they should now last forever)

Step 2

Assembly is the reverse of above.. check the alignment of the new goobers with the 3 fin drive flange on the bike – there are cutout marks on the alternator portion to help you line it up (this isn’t mentioned in any manual I’ve found, but was obvious to me once I tried to figure out HOW to line them up).

When done, start bike and listen to quieter engine! (at least it seemed like this to me at 12AM last night..)

Step 3

Reset clock if you have one when done.


Don Eilenberger

Alternator Drive Dampers Tip

By Frank Glamser
January 2000

I’d like to submit a brief tip to add to Don Eilenberger’s article on replacing the alternator drive dampers on a K-bike.

The hardest part in replacing the rubber alternator drive dampers is lining up the damper holder with the alternator drive vanes. It is impossible to see what you are doing as you try to mesh the two parts.

Two things can make things much easier.

Using a felt marker, mark the outside of the damper housing where the gaps in the goobers are located so you will know where the vanes will slide in. Using the rear wheel and fifth gear rotate the engine to place one of the drive vanes in the 12 o’clock position. Now you will know where the vanes are, even though you can’t see them.

Rotate the damper housing to place one of the gaps at the 12 o’clock position, and then visually guide the alternator into place using the mark and your knowledge of where the vertical vane is located.

The silicone grease Don Eilenberger recommended will help hold the goobers in place during the operation.

Frank Glamser
Hattiesburg, Mississippi
1992 K75RT BOOF #136
Mississippi tag IBMWR

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