I noticed that the the bike wasn’t charging very well when the electrical load was increased, such as when the headlight was on. I checked the diodes on the diode board and replaced the original rubber mounts with metal ones. This avoids having the board short out when the rubber mounts break and improves the grounding of the board so output from the alternator should be steady. But, I did not find any open or shorted diodes on the board which can cause a significant drop in charging current from the alternator as it passes through the diode board. You can read about how I did that work here:
So the next step is to replace the alternator brushes. As they wear down, the pressure from the spring decreases and this can reduce the output from the alternator.
Removing the Stator
The brushes are attached to the outside of the stator housing. Before removing the front cover, I removed the battery ground and inserted it into a plastic tube so there is no chance it can accidentally touch the frame while I’m working.
Then I remove the two screw holding the front cover and carefully remove it. I had to rotate the oil cooler to get a bit more clearance between the oil cooler bracket and the cover. The stator housing is at the bottom of the timing chest. There are three wires connected that are from the three electrical phases generated by the alternator. Mine are colored, Red, Black/White and Green from the upper left to lower right.
In the close-up you can see that the phases are lettered “U”, “V” and “W”, so the correspondence of colored wires to phases is Red-(W), Black/White (V) and Green (U).
I remove these wires. I also remove the brown and black wires that connect to the terminals on the white plastic brush holder at the top of the alternator. The Brown wire goes to the D- terminal on the left and the black wire goes to the D+ terminal on the right. Then I use 600 grit wet/dry paper and clean up the metal spades to remove the oxidation. There is quite a bit of it on the alternator phase terminals. I spray them with contact cleaner and inside the plugs that fit over the spade terminals and insert the plugs on the terminals several times to help clean any oxidation off the inside of the plugs.
Then I remove the nuts securing the metal terminals to the brush holder housing.
I remove the three Allan head bolts securing the stator to the timing chest cover.
I carefully remove the stator housing and the stator wiring being careful not to nick the stator wiring as that can damage the varnish insulation on the wires leading to shorts.
This exposes the rotor that spins inside the stator wiring coils. The copper slip rings are tarnished, so I use some 600 grit wet/dry paper to polish them so they are bright and shiny.
Removing the Brush Holder
I can get to the nuts on the inside of the stator cover that hold the brush holder to the cover. I find that by carefully pulling the stator wiring coils out of the housing, I can get a 8 mm socket on the nuts and loosen them.
Facing the inside of the stator cover, the left nut (DF terminal) includes two insulating washers and the bolt passes through an insulating spacer. The right nut (D- terminal) and bolt are not insulated from the stator cover. It’s important to be sure the insulating spacer and washers go back on the correct side when attaching the brush holder to the stator housing.
Remove and Replace Brushes
I use a small screw driver to push up the end of the coil spring that pushes the brush down inside the sleeve of the brush holder so I can pull the brush out the sleeve.
The old brushes are worn quite a bit when compared to the new ones.
I use a 100 watt soldering gun and to remove the soldered pig tails of the old brushes from the holder. I pull off the insulating tubes from the old brush pig tails and insert them onto the pig tails of the new brushes.
I insert the pig tails into the holes in the metal tab of the brush holder and solder them.
The sleeves that the brushes slide into have a ridge on the inside edge.
This is where the wires go so that the brushes can smoothly move up and down inside the sleeve.
Reinstall the Brush Holder
I insert the insulating spacer on the (DF) hole and one of the insulating washers on the back side of the brush holder so it sits between the stator cover and the holder.
I put the second insulating washer on the inside of the stator housing and then the metal washer and the nut and tighten the nut.
I connect the other stud of the brush holder with a nut and washer.
The coil springs often unwind a turn when they the end is removed from the top of the brush. I wind them one more turn and then insert the end on top of the brush. I check that the brushes slide smoothly inside the sleeve.
Reinstall the Stator and Housing
Then I carefully insert the stator housing and stator wiring coil over the rotor again being careful not to nick the stator wiring on the rotor or the housing. Since the brushes have the springs pushing down on them, I carefully lift them up as I fit the stator housing over the rotor. I tighten the three Allan bolts.
I check to be sure that the brushes are centered on the slip rings and check again that they can slide up and down freely inside the sleeves.
I attach the brush terminals and then the wires being sure the brown wire goes on the (D-) terminal and the black wire goes on the (DF) terminal.
I attach the alternator phase output wires at the bottom so the red wire is on the left, the black/white in the middle and the green on the right terminal. Then I attached the black wire to “Y” terminal on the left side of the stator housing.
Test Alternator Output
Before I put the front cover on, I attached the battery ground to the engine with the speedometer cable bolt and then started the bike. I verified that the generator light went out when the RPM increased. Then I attached a volt meter to the battery (+) or red terminal and the black lead of the meter to the frame. I verified the voltage increased as the RPM increased with a maximum of 15 volts and then as RPM continued to increase, it dropped back to 14.5 volts. This shows that the alternator is charging the battery and the voltage regulator is working to limit the charging voltage to 14.5 volts.
It looks like the cause of the low charging voltage was not a large diode going bad in the diode board, but likely worn brushes and a lot of oxidation on the alternator terminals.
I remove the battery ground cable and attach the front cover and then reattach the battery ground. Once more, I verify that the alternator is producing a steady 14.5 volts when the RPM is increased.