12 BMW 1973 R75/5 Replace Alternator Brushes, Paint Starter Motor

The alternator brushes have been in service for 97,500 miles and 40 years, so it is time to replace them with new ones.

Parts List

I got my brushes from Euro Motoelectrics here in Denver, CO. They stock electric parts for BMW and other European bikes.  They also have hardened bolt for removing the alternator rotor from the crankshaft nose.

Part # Description Qty
12 31 1 244 480 Alternator Carbon Brushes, Set 1
Rotor Puller Bolt and New Brushes

Rotor Puller Bolt and New Brushes

Removing the Stator

Since the engine is out of the frame, I didn’t need to disconnect the ground cable from the battery before removing the timing cover as it’s already disconnected. The brushes are in the white plastic holders at the 2:00 position.

Alternator and Wiring

Alternator and Wiring

There are three wires attached to the stator housing to remove, a brown, green and three pin black cable. I marked the stator housing next to the lugs with “B”rown and “G”reen to be sure I got them back on the right lug.

Alternator Brushes inside White Plastic Housing

Alternator Brushes inside White Plastic Housing

Labeling Wiring on Stator Housing

Wiring Labels on Stator Housing

I pushed the brushes outward until the springs were exposed and then hung the fingers on the edge of the white plastic housing so I can slide the brushes out of the holders.

Hooking Brush Spring to Top of Brush Housing

Hooking Brush Spring Fingers on Top of Brush Housing

There are three bolts holding the stator housing on and I remove those.

Removing Stator Housing

Removing (3) Stator Housing Bolts

I used a screw driver to gently nudge the stator out of the casing that is slides into being careful to not let it drop onto the floor.

Stator Coil from Inside

Stator Coil from Inside

This exposes the rotor the spins inside the stator to generate electricity when the engine is running.

Rotor Exposed

Rotor Exposed

Removing the Old Brushes

Next, I removed the nuts holding the lugs on so I can easily get a soldering iron to where the pigtails from the brushes are soldered to the brackets. I need a 260 watt soldering gun to melt the solder. The brush pigtail solder to a large bracket and my smaller 140 watt gun didn’t have enough heat to melt the solder.

Old Brushes Removed from Holder

Removing Wiring Lugs; Old Brushes Removed from Holder

Here is the old brush and the new one. You can see how much of the old brush has been worn away. I used some steel wool to clean up the lugs.

New Brush (Top) and Old (Bottom)

New Brush (Top) and Old (Bottom)

Installing the New Brushes

There are insulating sleeves on the old brush pigtails that I removed and put on the new brush pigtails.

Original Insulation Pig-tails

Original Pig-tail Insulating Sleeves

Insulation Pig-tail on New Brush Wire

Insulation Sleeve on New Brush Pigtail

I cleaned out the holes in the bracket for the brush pigtails using a drill bit. I installed the new pigtails into the holes and soldered them to the bracket being sure the solder flowed into the copper strands of the pigtail.

New Brushes Installed

New Brushes Installed

Cleaning Stator Housing & Rotor Pickup Contacts

I used Autosol Aluminum cleaner to clean up the stator casting. I used contact cleaner and a small file to clean the lugs for the three wire connector.

The rotor contacts were blackened from the brushes so I used Autosol metal polish to polish them up.

Dirty Alternator Contacts

Dirty Alternator Pickup Contacts

Polished Alternator Contacts

Polished Alternator Contact Pickups

Installing the Stator

Before installing the stator housing, I pulled up the brush springs so the fingers were on top of the brush housing to keep from damaging the brushes when I install the stator.

Brush Springs On Housing

I lined the stator up with the bolt holes and carefully rocked it until the  edge of the stator slipped under the retaining ridge of the engine housing. With a rubber mallet I very gently tapped the perimeter of the stator housing so it slide about half way into the engine housing.

Tapping the Stator Into Housing

Then I threaded the bolts into the holes and tightened them about a turn in order going around the edge until they were snug. I checked the gap between the stator housing and the engine to be sure it was uniform. I snugged up the stator mounting bolts being careful to not over tighten them and strip out the holes.

I checked the brushes to be sure they were aligned with the rotor contacts.

New Brushes Aligned on Slip Rings

Repainting the Start Motor

I removed the starter motor. There are three bolts, two in the rear and one in the front that is accessible from a cutout in the timing chest cover. I wire brushed them to remove the rust and old paint. Then I taped over all the electric contacts, the rear bearing and the front opening with the starter gears to keep paint out.  I sprayed the motor and the starter solenoid housing with black gloss enamel. I cleaned up the engine cavity that holds the starter and then installed the motor back into the engine. It’s best to align the front hole and start the front bolt before tightening the rear nuts. I torqued the rear nuts to 15 FOOT/pounds.

Cleaned and Painted Starter Motor

Cleaned and Painted Starter Motor

Painted Starter Motor Installed

Painted Starter Motor Installed

2 thoughts on “12 BMW 1973 R75/5 Replace Alternator Brushes, Paint Starter Motor

  1. Pingback: 1973 BMW R75/5 Rebuild: Replace Alternator Brushes and Front Crankshaft Seal | Motorcycles & Other Musings

  2. This is my first with a older BMW it seems to be very helpful but bikes are like people they all have their problems and their own twist, expect a curve or two

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