Starter Motor Cleaning Tutorial By Robmack
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 accessible once the ECU / tool tray 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:
  • #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.

2. Using the Philips screwdriver, loosen and remove both screws holding the motor together

3. Remove the top cap by sliding it up over the pinion gear.

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

5. Carefully remove the endcap and slide the rotor from the brush holder. Note that the brushes are sprung.

Using a toothbrush and contact cleaner, scrub the commutator ring on the rotor free of carbon dust.

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.

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).