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Starter Motor overhaul on a 1992 BMW K75S

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mnbikerguy

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The articles, posts and comments in this tech section are posted by individual members and reflect their personal thoughts and experiences with repairing, maintaining, and generally working on motorcycles. This information may require specific knowledge and skills, may or may not be correct or current to model.

The authors of information found here and the BMW MOA take no responsibility for ensuring the accuracy of any information (including procedures, techniques, parts numbers, torque values, tool usage, etc.), or further for any damage of any kind or injuries incurred or caused by anyone following the instructions or information found here.

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Intro:

Overhauling the starter motor is not that difficult and hopefully the step-by-step process IÔÇÖve outlined below will make it as straightforward as possible. The first step is to decide whether you want to just clean the starter commutator or if you want to replace the brushes as well. I found that replacing the brushes was relatively inexpensive and did not involve much extra work so thatÔÇÖs what IÔÇÖve outlined in this DIY article. The part numbers I ordered are as follows:
12411459445 (O-rings)
12411459567 (Brush connected to ground wire nut)
12411459297 (Brush plate)

Steps:
  • Locate starter motor
  • Remove and disassemble starter motor
  • Clean/overhaul starter motor
  • Reassemble and install

Supplies needed:
  • Replacement brushes and misc. parts
  • Brake cleaner
  • Scrub pad/wash cloths
 
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Step 1 (Pic 1)

Put your bike on the center stand, lift up the seat and pull out the storage compartment/fuel injector module. Pic 1 was taken after step 1 was completed. Notice the two red arrows IÔÇÖve added to the picture. They point to the two mounting bolts on the starter motor (near the left side of the battery).
 

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Step 2 (Pic 2)

Remove the battery, which will give you access to the starter motor. Pic 2 was taken after the battery was removed. Notice the two red arrows IÔÇÖve added to point out the two mounting bolts on the starter motor. Also notice the plastic cover outlined in blue which partially obscures the starter motor.
 

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Step 3 (Pic 3)

Remove the three bolts holding the plastic cover in place on the left side of the bike and pull it back to fully expose the starter motor. Pic 3 shows the three bolts on the plastic cover. The same cover can been seen from a different angle on Pic 2, again outlined in blue.
 

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Step 4 (Pic 4)

Remove the two mounting bolts and the nut which secures the ground wire. IÔÇÖve added three red arrows to point these out on Pic 4.
 

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Step 5 (Pic 5)

Pull out the starter motor. This can be a little tricky, you might need something like a rubber glove that gives you a better grip on the starter motor as it took a bit of pulling for me to get it out. Pic 5 shows what it looks like after the starter motor has been removed.
 

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Step 6 (Pic 6)

Mark the end caps on the starter motor, relative to the cylinder case between the caps. Pic 6 shows the starter motor after being removed. IÔÇÖve indicated with two red arrows the contact points between the end caps and the central cylinder case. Mark one end with a single slash and the other with a double slash so you can tell which end is which. I ended up using a black felt tip marker to make the slashes. This step is just so that the two end caps and the cylinder case go back together in the same position.
 

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Step 7 (Pic 7)

Remove the two bolts that hold the starter motor together. Pic 7 clearly marks these two bolts.
 

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Step 8 (Pic 8)

Pull the end caps apart to reveal the inside of the starter motor. Pic 8 shows one end cap on the right, the armature in the middle (notice the copper part, aka the commutator, is dirty) and the cylinder case on the left. The other end cap of the starter motor is off to the left of the cylinder case, out of view. IÔÇÖve added four red arrows to this picture to show where the replacement parts will go.
 

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Step 9 (Pic 9)

Lay out the replacement parts. Pic 9 shows the replacement parts, which IÔÇÖve identified with four arrows that roughly correspond to the four arrows on pic 8.
 

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Step 10

Swap out the old parts with the new parts. The O rings are easy enough to replace. I coated them with a small amount of oil to make sure they would seal properly after I put the motor back together. Replacing the brushes and the brush holder is a little bit tricky. Just look at how the old parts are positioned and replace them with the new parts in the same position.
 
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Pic 10

This is an up-close pic of the dirty commutator before cleaning.
 

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Step 11 (Pic 11)

Clean the copper part of the armature (the commutator). The dirt thats on there looked to be residue from the old brushes (they wear down over time). Its difficult to clean off with conventional cleaners and Ive read others like to use brake cleaner for thiswhich I wish I would have had. Pics 10 & 11 show the before and after cleaning shots of the copper part of the armature.
 

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Step 12

Put the starter motor back together. For me it was tricky to get the brushes to sit properly inside the end cap and on the copper part of the armature at the same time, so be patient. Once the end caps are in place make sure to line them up relative to the cylinder case (this is why you marked them in step 6). Screw back in the two bolts that hold the starter motor together. Then try turning the spindle to make sure the brushes are in good contact with the copper part of the armature.
 
Step 13

Put the start motor back on the bike. Just do the reverse order of how you took it out. Finally, screw the plastic cover back on and put the battery back in. Prestoyoure done. Feel free to send me an email if you have any questions.
 
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