Are my Alternator Brushes Cooked?

Hey Everyone,

I've been going through my bikes electrical as I have been noticing my battery does not seem to be getting charged while riding.

One point of possible concern I have are my alternator brushes. I can see the lines on both of them and am wondering if this indicates that they need to be replaced.

From the picture, I used a mechanical pencil to measure their height and put them at ~.45 inches in length.

I also tried cleaning up the copper ring in there with the eraser of said pencil, but it looks like I will need to use something more effective.

Cheers,

 

someone will correct me if wrong, but the service limit on a brush is 10mm (0.39"). Full length is 17mm (0.67")
I'm not sure if that's total length or as you have measured.
Either way, I'd say they're fine.

The battery doesn't get charged below 3000rpm.

I'd suggest wiring up a voltmeter and monitoring voltages with it off, cranking, and above 3000rpm

 

at bottom of this link there is info on charging system
https://www.xjbikes.com/forums/threads/the-ultimate-relay-switch-sensor-and-diodes-guide.27543/


quick excerpt

If your charging voltages are too low, suspect the alternator brushes first, then perform the alternator stator and rotor checks as described in the Alternator Section.

If your charging voltages are too high, suspect your Regulator - Rectifier unit first, and perhaps dirty or corroded electrical terminals. The procedure for checking these is too detailed to describe here, and you should consult your service manual for additional details.


5) Check the condition of your main circuit terminals.....they should be zestfully clean and uncorroded, or you're primed for a variety of problems......not only will your circuits not be getting full power out of your battery, but to add insult to injury, your charging system may think that the battery needs more juice, and so it starts cranking out amps like there's no tomorrow. It's pretty safe to say that neither of those two occurrences qualify as a Good Thing (tm), so...........start at the beginning, and inspect and clean (and then protect, like with di-electric grease or equivalent) all the [/b] terminal connection points[/b]:

* the positive battery post connection to the positive battery cable.
* the positive battery cable connection to the starter relay (or "solenoid").
* the main harness terminal connector from the starter relay.
* the main lead from the starter relay to the starter motor (both ends).
* the "main fuse" contacts inside the fusebox.
* the battery ground cable contacts at both the engine case and at the negative battery post (poor ground are just as bad as poor positive feeds; after all, it takes two to tango, or to complete a circuit, and electricity doesn't care where the restriction occurs).

 

.45 inch is 11.43 mm

from catalog which is full of links about charging system
https://www.xjbikes.com/forums/threads/xj-parts-catalog-section-d-electrical-system.44641/

NOTE: Alternator brushes should be replaced whenever they are less than 11mm in overall length......the factory maintenance interval indicates that you should expect to replace these brushes every 8-10,000 miles. Factory brushes have "wear marks" (scribed lines) on the brush to indicate their wear limit; these aftermarket brushes also have the scribed wear line. Overall length of these brushes are 17.10mm, with 9mm of length from the wear bars to the contact end of the brushes:

 

I should clarify that I have the 11.43mm of brush that is exposed but don't know the overall length. I tried removing the screws holding the plate to the case cover only to find them extremely stuck on and a high risk of stripping completely with my JIS screwdriver.

 

ok is see what you are saying.
clean copper rings with a hard art eraser or CROCUS CLOTH. wipe down with some electronic contact cleaner on clean rag
then measure ohms across rings and measure stator ohms

sounds like you have some connector cleaning to do .
battery may be bad do a spicifig gravity test if it is lead acid . add distilled water if needed to fill to lines.
when you charge battery and then let it sit over night it should read 12.8 volts after full charge

 

Nambro, if you look at the picture you posted you can see you can still wear the brushes down to the wear line. There is a lot of life left.

 

Will do, hopefully cleaning the rings will do the trick and I still have some poking around with the multi-meter to do.

Battery:
AGM battery is new, purchased a couple weeks ago, and reads 12.97V at the terminals with bike off
When starting the bike but before the engine is running, the voltage does not dip below 9.5V

Problem:
Voltage at the terminals with the bike running won't increase past 12.65, even when running at 2,500 rpms.

Next Steps:
- Deep clean of the rings
- Check for loose wiring/ corroded connectors

I need to check and will report back after recording:
- Alternator Stators. From reading, should be ~.46 ohms across each pair
- Resistance across lead wires on alternator rotor. From what I've read, should be ~4 ohms


I have also read in this thread: https://www.xjbikes.com/forums/threads/update-help-electrical-gremlins-strike-again.27387/ about the alternator being plugged into the wrong connector at the wiring loom. I'm not familiar with this but I have come across some mis-wiring on my bike from the PO so it may be something I should look into.

 

Had a spare moment to run out to the bike, some additional pictures:

The first picture is something I think I should be concerned about. It looks like the wires coming off the stator were making contact in two places with the copper face and it appears to have rubbed through the rubber casing. I'll wrap with electrical tape and test the legs for shorts.

You can see the copper face is far from clean, but what is interesting is that I hit it with an eraser/wiped it down yesterday and it was much cleaner than this before I fired it up again today.

 

Nambro, did you ever solve this problem? I'm curious what the resistance was between the two rings and also between the three white wires of your stator. I have an XJ1100 an fried a few things recently, like my 2-3 coil and the alternator rotor (field coil). Popped that off today and am waiting for my 38 year new replacement...fingers crossed.

 

specs and info on charging system are found in this link as well as ignition system
The Ultimate Relay, Switch, Sensor, and Diodes Guide



Checking Alternator Stators:
0.37 ohms +/- 10% for all XJ1100 models.

Checking Alternator Rotors:

4.0 ohms +/- 10% for all XJ650, all XJ700, all XJ750, XJ900RK, and XJ1100 models.

 

Thanks XJ550H. I think the 4.0 ohms on the rotor is important but 0.37 ohms on the stator coil? If it's 0 resistance with continuity, all good in my opinion.

Dialing in the resistance of the coil-plug wires-caps-plugs as a system is critical too. Can't change one part without taking the resistance of the others into consideration. Bike runs so much better when per stock specs (i.e. non-resistant plugs, 5K caps).