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Thread: Starter Motor overhaul on a 1992 BMW K75S

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    Registered User mnbikerguy's Avatar
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    Starter Motor overhaul on a 1992 BMW K75S

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    Intro:

    Overhauling the starter motor is not that difficult and hopefully the step-by-step process I‘«÷ve 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 that‘«÷s what I‘«÷ve 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
    Last edited by mnbikerguy; 05-24-2011 at 11:58 AM.

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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 I‘«÷ve 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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    Last edited by mnbikerguy; 05-24-2011 at 02:39 PM.

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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 I‘«÷ve 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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    Last edited by mnbikerguy; 05-24-2011 at 02:40 PM.

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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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    Last edited by mnbikerguy; 05-24-2011 at 02:41 PM.

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    Step 4 (Pic 4)

    Remove the two mounting bolts and the nut which secures the ground wire. I‘«÷ve added three red arrows to point these out on Pic 4.
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    Last edited by mnbikerguy; 05-24-2011 at 02:41 PM.

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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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    Last edited by mnbikerguy; 05-24-2011 at 02:41 PM.

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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. I‘«÷ve 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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    Last edited by mnbikerguy; 05-24-2011 at 02:42 PM.

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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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    Last edited by mnbikerguy; 05-24-2011 at 02:42 PM.

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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. I‘«÷ve added four red arrows to this picture to show where the replacement parts will go.
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    Last edited by mnbikerguy; 05-24-2011 at 02:43 PM.

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    Step 9 (Pic 9)

    Lay out the replacement parts. Pic 9 shows the replacement parts, which I‘«÷ve identified with four arrows that roughly correspond to the four arrows on pic 8.
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    Last edited by mnbikerguy; 05-24-2011 at 02:43 PM.

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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.
    Last edited by mnbikerguy; 05-24-2011 at 02:33 PM.

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    Pic 10

    This is an up-close pic of the dirty commutator before cleaning.
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    Last edited by mnbikerguy; 05-24-2011 at 02:38 PM.

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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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    Last edited by mnbikerguy; 05-24-2011 at 02:44 PM.

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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.

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    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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