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1Back to top Go down   Starter Motor Cleaning Tutorial Empty Starter Motor Cleaning Tutorial Wed Jun 29, 2011 10:34 pm


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The K100 starter motor is an integral part of the grounding circuit for the motorcycle. Since the motor's brushes wear down with time and use, carbon dust from the brushes settles around the commutator of the rotor inside the motor, eventually causing poor conductivity. There are often many electrical problems which can be attributed to dirt in the starter motor.

It takes very little time and effort to clean the starter motor. This tutorial will go through the steps to remove, disassemble, clean and reassemble the starter motor.

The starter motor is located under the seat, low down on top of the gear box, between the battery and the engine. The starter motor is on the left side of the motorcycle, the alternator on the right side. the starter motor is the smallest of the two. It is mounted to the gearbox using two M8 screws, both accessable once the ECU / tooltray is removed from the bike. To remove the starter motor:

  1. Lift the seat, remove the Fuel Injection Computer connector and withdraw the tool tray.
  2. Disconnect and remove the battery for greater accessability
  3. Use a 8mm wrench to loosen the nut connecting the electrical wire to the binding post on top of the motor. Replace the nut so as it will not be lost.
  4. Loosen and remove the two M8 screws holding the starter motor to the gearbox
  5. While carefully wiggling the motor side to side gently, pull it backwards towards the rear tire. The motor will eventually withdraw.
You will need the following tools for the cleaning:
Starter Motor Cleaning Tutorial IMG_9465

  • #2 Philips screwdriver
  • contact cleaner, such as Deoxit
  • toothbrush with nylon bristles
  • permanent marker
The disassembly process is as follows:

1. Use the permanent marker to draw reference marks on both end caps and the stator housing of the motor. These reference marks will be used when reassembling the motor to make sure parts are lined up.
Starter Motor Cleaning Tutorial IMG_9467

2. Using the Philips screwdriver, loosen and remove both screws holding the motor together
Starter Motor Cleaning Tutorial IMG_9469

3. Remove the top cap by sliding it up over the pinion gear.
Starter Motor Cleaning Tutorial IMG_9470

4. Carefully remove the stator housing. There are very strong magnets in this housing which will put up strong resistance. Be careful. Make a reference mark on the brush holder that lines up with the endcap reference mark
Starter Motor Cleaning Tutorial IMG_9472

5. Carefully remove the endcap and slide the rotor from the brush holder. Note that the brushes are sprung.
Starter Motor Cleaning Tutorial IMG_9473

Using a toothbrush and contact cleaner, scrub the commutator ring on the rotor free of carbon dust.
Starter Motor Cleaning Tutorial IMG_9475
Similarly, clean the brush holder, being careful around the fine wires that connect to the brushes. If the topcap is dirty, clean it also with the toothbrush and cleaner. Avoid the ball bearing on top of the rotor as it should not be cleaned of oil or grease. Inspect the O-ring on the top cap; replace this ring if it is deteriorated because it seals the opening through which the motor is inserted, preventing oil leakage. It should not be necessary to clean the stator.

To reassemble the motor, follow the steps above but in reverse order. Push in the brushes while inserting the rotor through the brush holder. Assemble the stator housing over the rotor followed by the topcap, making sure that the reference marks line up. There are detents on the housing that will ensure the parts do not rotate relative to each other. When the parts are assembled, insert both screws and tighten them down. Make sure the parts are properly mated by rotating the pinion gear by hand.
Starter Motor Cleaning Tutorial IMG_9478
It should be smooth with no binding.

Remount the starter motor back on the bike. Make sure the motor is inserted into the engine case firmly before screwing it down. Reattach the electrical wire to the binding post and secure it with the nut to make a positive contact. Reinstall and connect the battery, replace the tool tray and connect up the Fuel Injection Computer (remember to clean contacts with Deoxit or similar if this has not been performed recently).

Last edited by robmack on Thu Jun 30, 2011 10:29 pm; edited 4 times in total

1987 K75

2Back to top Go down   Starter Motor Cleaning Tutorial Empty Re: Starter Motor Cleaning Tutorial Wed Jun 29, 2011 11:03 pm


Eggsellent work, Robmack!

One thing...note that there's an O-ring round the snout of the starter motor which must be carefully handled so as not to cause oil leaks. Be sure it's in good nick before replacing the now-cleaned up starter motor into the engine housing.

OK, two things...the ECU connector is removed by unscrewing the miniature screw holding the connector in, with a small Phillips head screwdriver, then using a flat screwdriver (or some such tool) in the small hole in the base of the tooltray, work the small metal tab thingy in one direction until it allows the connector to come free from the ECU. Deoxit that connector while you're there.


3Back to top Go down   Starter Motor Cleaning Tutorial Empty Re: Starter Motor Cleaning Tutorial Thu Jun 30, 2011 10:19 am


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Top job robmack well layed, I did mine some time back and can endorse the reasoning behind a clean up a general check up and pease of mind.



4Back to top Go down   Starter Motor Cleaning Tutorial Empty Re: Starter Motor Cleaning Tutorial Thu Jun 30, 2011 12:04 pm


good tutorial rob .....

im guessing those nice pics will make it appear non confronting for many that would prefer not to play with electrical/mechanical "DARK ART "things.

whilst in there things up ...

observe the springs that hold presure on the brushes ...and make sure that they arent corroded and binding to the brush holder

make sure that there is adequate length in the brushes them selves ,,,,this will be confirmed on the removal of the brush backing plate from the armature are looking for good tension and no sideways movement of the brushes within their confines

....if there is movement ...the rebuild kit is verry reasonably priced and if in doubt put one in whilst your there .

thirdly check for black segments of the armature ..(more likely if the brushes are particuarly worn) if found ,
use scotch bright ( a "3m" green material commonly used for dish washing and stuff around the sink)
to scuff up the segments so a good carbon to copper finish is acheived,,,,swab off the cleaning process with contact cleaner and a rag .

NOTE do not go overboard doing this ....deformation of the armature could spell an early death of the whole assembly
and caution should be applied to the areas where the windings are soldered to the comutator segments (keep away)we are not trying to strip the enamel insulation off those cables.

hope this helps someone .

cheers blokes


5Back to top Go down   Starter Motor Cleaning Tutorial Empty Re: Starter Motor Cleaning Tutorial Fri Jul 01, 2011 4:53 pm


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Excellent stuff Rob.


6Back to top Go down   Starter Motor Cleaning Tutorial Empty Re: Starter Motor Cleaning Tutorial Sat Jul 02, 2011 2:12 am


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Thanks for this guys. It's on my "to do" list. Very clear and easy to follow instructions with ad on's. Always great to get advice from those who have done it. Smile


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