66K on the alternator...

[deancox]

Towards the end of a full day of riding this past Friday, my alternator (battery) light began to glow intermittently and only "softly" not real bright. After about 50 miles it stopped and did not come back on for the last 60 or so miles. The next day it did not come on at all when I rode the bike around the block.

I know I can pull the alternator and check it out and rebuild it myself, but this is one of those things that it seems smarter to have a pro rebuild it. It is one of the keys to so many things you want to work well on your bike that kind of like having a heart surgeon who does 100 surgeries a year do your critical surgery rather than a guy who is reading a book to get it done....

I will probably just yank it and have it done before it poops out.

Any thoughts

[Motor31]

Sounds like the brushes are worn. That really isn't a big job and you should be fine with it. The Pro's are for jobs like the windings being fried or the contact points on the armature need to be machined smooth.

Clean the contact rings and look at the brushes, chances are they are just worn.

[jdiaz]

Don't do anything until you have that battery load-tested. The fact that the problem "went away" makes me wonder if its battery instead of the alternator. The brushes in these bikes are pretty robust. Get a digital voltmeter, attach it across the battery, and see how the charging system is working.

Another thing: does this bike have any sort of tail light enhancement kit? I have this stuff on my bike, and the alternator light comes on faintly when all those tail lights are activated. Maybe its a brake switch issue?

[breyfogle]

At about 110K miles, my K75S developed very similar symptoms. After mounting a small pocket volt meter to the handlebar pad and direct wiring it to the battery, I road around town for an hour or so. The alternator was obviously mis behaving, some times it would work just fine, sometimes it would produce rather erratic voltage readings. Anyway, I pulled the alternator. The brushes were obviously near or past their wear limit. By itself this is an easy fix but in my case the slip rings that the brushes ride on were also VERY deeply worn. I chose to have an alternator shop rebuild the whole thing.

One thing I learned when looking for a shop was to just ask "do you rebuild Bosch alternators". If I mentioned "BMW" of "motorcycles" the answer was "no". If I mentioned "Bosch" the response was usually "sure, we do that".

[deancox]

Don't do anything until you have that battery load-tested. The fact that the problem "went away" makes me wonder if its battery instead of the alternator. The brushes in these bikes are pretty robust. Get a digital voltmeter, attach it across the battery, and see how the charging system is working.

Another thing: does this bike have any sort of tail light enhancement kit? I have this stuff on my bike, and the alternator light comes on faintly when all those tail lights are activated. Maybe its a brake switch issue?

battery is almost new, no brake light enhancements.

[jdiaz]

See if you can get the battery checked just in case. I've had a new one fail before, and I rode the bike until the alternator brushes gave up. It was a bright sunny day, and I never saw the alt light on until the bike just stopped with 5.96 volts trickling out of the battery. My wife had to tow me with her old-tech R75/5. :laugh

Follow what breyfogle says. Its easy to remove the two screws holding the brush/regulator assembly with the alternator in the bike (you just have to move the coolant recovery tank), and replacement is about $70. Hopefully the slip rings are ok.

And if you do have to get another alternator, don't rebuild the stocker. Just upgrade to the 700w unit from the later bikes.