How to fit brushes to b+s 12 hp starter motor about 8years old

Mark, It can be tricky, use small ***** driver to push back brushes one at a time while working armature in place or if you can get a buddy to hold them both back while you slide armature in place.
Check the attached links,instruction and guides, Good luck
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How to rebuild Briggs and Stratton starter motor replacing bottom end cap...
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STARTER REBUILD on KOHLER KT 17HP Bobcat UTV Engine wmv
brush installation AVI

Disconnect the power
disconnect hoses
lay machine on it's left side
remove back cover screw and cover
slip belt off pully
unplug motor wires
undo bolts holding motor
pull motor to rear of machine
revome motor to bench
locate brush housings
undo retaining clip and slide out old brush
fit new brush
replete with other brush
reasonable in reverse of removal

If you had it apart and know your brushes are good, you could just order the part specified, but if I was you I would get the part and the brush kit. The brush wire actually has an eye fitting that bolts to the cap. You might have a pinched wire or, the wires might be brittle and when you go to remove the brushes, could break apart.
For your parts, google the number along with Kohler and see if you cant get it cheaper from somewhere else. In my experience, Sears is only comparable if they stock it in store and you live near by.

There are often tiny pin holes in the casing, depending on the starter. Pull brushes back and insert a paper clip into the small holes to hold brushes off commutator. Slide the armature back in, then pull out the paper clips. This will allow the brushes to spring onto commutator rotor.

Begin by diassembling the motor. Keep close track of the orientation of the brushes & other components. Inspect the brushes & the commutater. The commutater is the brass colored area where the brushes ride. The commutater should have a smooth surface. A short can cause roughness at times. If it passes a visual inspection; You next need to test the resistance of the rotor. There should be a division on the commutater. Using an Ohm meter. Measure the resistance between these. An out of limits or OL measurement would imply a bad rotor. I am uncertain to what the proper spec should be but as a general rule, 0 ohms & OL would indicate a fault. Beyond those items, inspect obvious things such as burn marks and open or shorted wiring to the brushes.

Hi,iI have just had the same fault, and as described elsewhere, the solution was to replace the motor brushes. I would say this took 1/2 - 3/4 hour to remove brushes and same to replace.
How:
1.DISCONNECTED ELECTRICITY SUPPLY
2. Disconnected water
3. Removed the 1 screw from back panel, removed panel to get access to remove belt.
4. Lay washer on it's side (2 people recommended)
5. From underneath machine, unscrewed 2 bolts on the motor (back of the machine)
6. Holding the motor so it did not fall and get damaged, carefully tapped end of motor to unmount it from holding pegs (slides towards back of machine)
7. Noted how the plastic cover fixed to motor, then snipped tie wrap holding it to motor.
8. Unplugged connector and earth connector.
9. Carefully removed connector on each brush.
10. AS THE BRUSH WAS SLOWLY WITHDRAWN, checked the orientation of the bevelled edge of the brush relative to the motor so the new one was fitted correctly (the end of the brush is angled so it sits flat against the motors commutator)
11. Replaced brushes and refitted in reverse order.

Take care

Apparently, although the two halves are screwed together, the unit is riveted to the pole. Those rivets appear to hold the housing together. On mine, it stopped rotating and I think the commutater brushes are bad. I may drill out the rivets, repair the motor and bolt the unit back to the pole (in place of the rivets). horny385, you are a **** and not clever or helpful.

The Mamco motor is WAY too much money.I bought brushes on E Bay and made them fit. #51591 takes 1/4 " square brushes.

On the Boxer motor, the starter is located at the back of the engine, usually a Denso or Fuji Heavy Industries own, and is held on with 2 13mm bolts. There is a 12mm nut on the main cable from the battery.

Remove the battery leads, negative (black) first, then the positive (red) lead and store the ends away from the terminals while you work.

Undo the 2 bolts holding the starter onto the bellhousing, and ease it backwards. Undo the 12mm nut securing the battery cable and put the nut back on the post, its brass and you should retain it as a steel one will strip the copper thread on the post.

Pull the single plug out of the back of the solenoid on the motor - that is the "start" wire from the ignition.

Swivel the end of the motor toward the rhs and it will come out sideways and upwards.

Refitting is the exact reverse of the above. The problem will be the carbon brushes in the starter motor, it can be easily repaired at an auto electrical shop instead of a new one. The solenoid slide bolt can be cleaned and lubed too, but brush replacement is not a home diy job, the solder joints need a LOT of heat to fit new brushes.

Hi. I have just had the same fault, and as described elsewhere, the solution was to replace the motor brushes. I would say this took 1/2 - 3/4 hour to remove brushes and same to replace.
How:
1.DISCONNECTED ELECTRICITY SUPPLY
2. Disconnected water
3. Removed the 1 screw from back panel, removed panel to get access to remove belt.
4. Lay washer on it's side (2 people recommended)
5. From underneath machine, unscrewed 2 bolts on the motor (back of the machine)
6. Holding the motor so it did not fall and get damaged, carefully tapped end of motor to unmount it from holding pegs (slides towards back of machine)
7. Noted how the plastic cover fixed to motor, then snipped tie wrap holding it to motor.
8. Unplugged connector and earth connector.
9. Carefully removed connector on each brush.
10. AS THE BRUSH WAS SLOWLY WITHDRAWN, checked the orientation of the bevelled edge of the brush relative to the motor so the new one was fitted correctly (the end of the brush is angled so it sits flat against the motors commutator)
11. Replaced brushes and refitted in reverse order.