87 K Bike Alternator Question

[Paul_F]

I went for a 50 mile ride today and then plugged the battery into the battery tender. Five hours later and the green light indicator had still not lit. Checked battery voltage level at 12.00ish. Turned the bike on and checked again. The battery level was 10.00ish. By the way, I did top up the battery level with distilled water a few days before heading over to West Bend, which would be two weeks ago.

Am I correct in assuming that the alternator is the source of the problem? If it is, is there a replacement that I can easily pickup at an auto store or should I simply go to the beemer dealer and have him do the complete fix?

Is this an easy fix or do you think that something else might be the problem? I had noticed while in West Bend that the idle level was much lower than usual.

[PGlaves]

I went for a 50 mile ride today and then plugged the battery into the battery tender. Five hours later and the green light indicator had still not lit. Checked battery voltage level at 12.00ish. Turned the bike on and checked again. The battery level was 10.00ish. By the way, I did top up the battery level with distilled water a few days before heading over to West Bend, which would be two weeks ago.

Am I correct in assuming that the alternator is the source of the problem? If it is, is there a replacement that I can easily pickup at an auto store or should I simply go to the beemer dealer and have him do the complete fix?

Is this an easy fix or do you think that something else might be the problem? I had noticed while in West Bend that the idle level was much lower than usual.

I would be more inclined to believe that the battery is the source of the problem. A quick test is simple. Attach a reliable multimeter set to measure DC volts directly to the battery terminals. Read the voltage. Start the motorcycle. Notice what the voltage drops to while the starter is cranking. Read the voltage with the bike at idle. Expect it to be a little lower than before the key was turned on. Finally, raise the RPM to 3,000 and read the voltage.

With a decent battery I would expect at least 12.4 volts key off. 12.7 to 12.8 is more like a good battery. Expect a drop during cranking but 11. something is as low as it should go. At 3000 RPM expect to see something in the high 13s up to about 14.2.

If you see the voltage go up at 3000 RPM but not up as high as it should be resist the temptation to blame the alternator. It is just as likely that the battery is resisting the charge and not allowing the voltage to read as high as it should with the battery in the circuit.

[breyfogle]

Your description sounds more like a battery problem. *If* the alternator is actually misbehaving, it's a very ordinary Bosch alternator that is easily rebuilt by any/most auto electirc shops that service Bosch stuff.

[Gilly]

Is there any specific problem with the bike, aside from you noticing the idle speed was lower in West Bend?? Or just chasing a green light in your charger??

Gilly

[Paul_F]

It is just the green light on the battery tender that is not coming on, just the red charging light. It took about 5 hours before the light turned green on the charger.

[Gilly]

Paul
If you take it out for a ride in the dark, is the red light next to the battery symbol coming on or not? If not, probably a non-issue, or if you don't know how old the battery is, might be worth swapping. Any long trips planned?

Gilly

[Paul_F]

Paul
If you take it out for a ride in the dark, is the red light next to the battery symbol coming on or not? If not, probably a non-issue, or if you don't know how old the battery is, might be worth swapping. Any long trips planned?Gilly

The red light does not come on and I had planned to leave for the Boston area this coming Friday.

I should mention that the bike and I went sliding up a gravel road in Colorado about a month ago. Some fluids spilled out before the bike was put upright again. When I topped up the battery before West Bend with distilled water, the bolts holding the battery and the top brace were coated with rust like substance which I cleaned up. As well, it looked like some of it fixed itself onto the centre stand, which I cleaned off and then painted.

[Paul_F]

The battery is two years old. However, it only just recently that i have begun to top up the battery. The remainder of the time I have relied on the mechanics at the 10,000 and 20,000 km services to check it.

[Gilly]

The last time I put a battery in I had a bit of cleaning and painting to do on my 'ol 87 too, so no big shock there.
I hate to have the diagnosis of a battery come down to what the battery charger manufacturer decides is "charged enought to turn on zee green light".
The charging system is probably in order if the red battery light is staying out (not even glowing), but the best test is what Mr Glaves points out, with a voltmeter on the battery and the engine running above idle (just set the choke all the way open) you should be at 13.8 to 14.2 volts.
As for the battery itself, again if you are "iffy" on age, let that be your guide, especially if you have a trip coming up. You could remove it and have it tested, but batteries are kinda funky in that you can test it and it's fine today, but 2 days later it poops out on ya. By now you're probably nervous enough about it that if you don't replace it before your trip you'll be agonizing over it the whole trip. I'd recommend getting one of these new gell cell or "AGM" batteries. I have one in my 75, I can get the name and model number for you if you want, it just barely fit.No leaking fluids when you go sideways, hhheh heh.

Gilly

[Gilly]

Just saw your last post, yeah at 2 years I don't think I'd sweat it Paul. IMHO anyways, I don't know what yo consider an acceptable risk, but at 2 years, hell I'd take off to California on a 2 year old battery. If it's cranking nice and fast don't worry about it.

[Big_E_Pants]

Yeah you may be safe and not get stranded but ... Driving on a "bad or suspect" battery can do more harm . Your alternator wil work very hard to bring the battery up to full charge ,if the battery is unable to recieve a full charge the alternator will keep working (the voltage regulator reduces the load on the alternator as the battery reaches full charge) thereby creating excess heat and as you probably already know heat under the tank is already pretty high !

The over worked alternator will overheat and have a much shorter life and if the bike is a little older (then so is the alternator) with miliage on it a "bad" battery can cause the Alternator to also go "bad" AND THAT CAN STRAND YOU !!!

100 buck's for a new battery and piece of mind vs. what for an alternator and Batteryand ruined trip.

[Gilly]

I wouldn't dispute that advice. Up to the owner and his comfort level. I do however believe that the battery could be tested, that would be the best IMO, UNLESS you really don't want to even trust a battery test.
Without having a single "real" symptom to go on, I think it's agonizing over nothing. BMW didn't decide when this GREEN light will come on on the charger, it may automatically drop down to a trickle, then stay at a trickle for awhile, then eventually come on, etc, NO way to diagnose anything.
Gilly

[BuddingGeezer]

2 years on a lead acid motorcycle, especially one that was turned over and lost electrolyte, is all I would chance. I have since gone to the Absorbed Glass Matt (ABS) batteries on my motorcycles. No sill, no topping with water, usually more power. I have a Welsco in my K100LT. I ran an Auto Zone ABS in a Kawasaki Vulcan for 2 years. A regular battery would not even start that bike when it was hot.

Ralph Sims

[Paul_F]

I did replace the battery this morning and it seems to be the fix needed. Thank you for all of your suggestions and help. As it turned out, it was easier to get the battery out than I anticipated. I am surprised and disappointed that it lasted a couple of weeks shy of two years, but I suppose that I have to assume some responsibility since I wasn't regularly monitoring the battery and replacing with distilled water when the levels were getting low.

Thank you again. It looks as if I'll be able to take on Friday for the Boston area.

Paul

[PGlaves]

I wouldn't dispute that advice. Up to the owner and his comfort level. I do however believe that the battery could be tested, that would be the best IMO, UNLESS you really don't want to even trust a battery test.
Without having a single "real" symptom to go on, I think it's agonizing over nothing. BMW didn't decide when this GREEN light will come on on the charger, it may automatically drop down to a trickle, then stay at a trickle for awhile, then eventually come on, etc, NO way to diagnose anything.
Gilly

Actually, 5 hours on a Battery Tender fresh off a 50 mile ride is a decent battery test. The green light blinks at 80% charged and comes on solid when the battery is fully charged. A decent battery after a 50 mile ride ought to at least reach the 80% level in 5 hours. If not, there is a problem somewhere that ought to be addressed. Maybe the charging system letting the battery go way down during that 50 miles - or maybe a battery that is about to go south. Worth checking in my opinion.

[Gilly]

I respect others opinions on this, but in my own opinion a battery charger makes a lousy battery tester.
I think the rider did the right thing if he wasn't comfortable with the battery any longer, especially with a trip coming up.
The battery performance (cranking speed) and the battery light (in the instrument cluster) are the best indications that you have a REAL problem, instead of a perceived problem due to the bike being laid down.

Gilly