Author Topic: alternator diagnosis..? (Read 4620 times)

jdirty · « **on:** July 12, 2011, 02:45:37 AM »

my power steering recently blew up, fluid everywhere, idk why. don't really care about it since i plan on taking it out. but i think fluid got into the alternator or it could've been coolant spill.. so i took out the alternator, inspected the brushes and from what i've been reading, voltage regulator. at first i just noticed that one of the brushes were pressed in, and there were a bunch of fillings, then i flipped it over and from the looks of it, mine is completely toast. i still brought it over to autozone though. i was pretty sure it was going to fail, i was just wondering if the test was going to say which parts failed, aside from the visually obvious candidate. but i guess not. the car starts when you jump it, but will eventually stall and shut down. evident with the radio first, then the with the tach. then the car dies. is there way to check the rest of the alternator..? open it up and look at it? or is there a way of testing resistance and stuff like that..? this is my first time dealing with electrical stuff.

(p.s. this is irrelevant but how do i resize photos within the post itself..?)

DesktopDave · « **Reply #1 on:** July 12, 2011, 07:05:48 AM »

That looks bad, but they're really overbuilt...might still be OK There are a few tests that I do on my bikes. A PM alternator is somewhat different, but I'll see what I can find for you. They sit in an oil bath on most bikes, so I wouldn't worry too much about oil on the coils.

Basically you have to test the individual circuits in the field coils and on the armature for breaks or high resistance. The diodes in the rectifier/regulator circuit are more likely failure points, but that's easily replaceable.

jdirty · « **Reply #2 on:** July 12, 2011, 05:39:48 PM »

umm.. i'm gonna go look for E36s and volvos in the yard for now.. i kinda got lost in your second paragraph..

DesktopDave · « **Reply #3 on:** July 12, 2011, 07:21:05 PM »

If you think that's complicated...read the link below. It's written by an Audi guy but we all use pretty much the same Dr. Bosch's magical mystery parts.
http://www.humanspeakers.com/audi/alternator.htm

I'd do three quick & painless tests myself:
1. With the motor off test the battery voltage between the terminals. Be careful not to short those terminals together, of course. You should see about 12.5VDC in reasonable temperatures, maybe a little less if the car has run recently. If you don't, get a trickle charger on that battery until it's well above 12VDC.
2. Next, a resistance test (ohms) from the battery negative to the frame. Should be really low, like 0.1 or something negligible. Then head up to the engine bay and do the same test between the intake manifold, ground stud and alternator housing. All should be negligible as well. You might have to scrape the probe a bit to get a good ground. If not, resolve those issues next by cleaning the grounds & lubing with a bit of dielectric grease.
3. Then turn on the motor...verify that the alternator bearings are quiet (no squealing or chirping); the belt is running nice and square with crank pulley and is tensioned properly. You'd be surprised at the number of times I've seen a bent mount arm or worn mount bushings. Any of those will cause the alternator to undercharge.

If all these tests pass, get that battery & alternator to either one good alternator shop/mechanic or three auto stores. Auto parts clerks don't know what they're doing sometimes and it really helps to have multiple opinions. Alternators and batteries can only truly be tested in use, load testing is a requirement.

DesktopDave · « **Reply #4 on:** July 12, 2011, 08:57:08 PM »

I read the other post...that regulator update might be a little less than you need. Looks like the brushes definitely shorted out with all that arcing damage. I'd definitely inspect the rotor contacts for damage at the very least...or get a spare used alt just for peace of mind.

I wonder if an M20 alt would fit? They're likely very similar if not identical. If I get a chance I'll take a look-see. There is a little conduit cover on the M42 version but it might just swap.

DesktopDave · « **Reply #5 on:** July 12, 2011, 09:14:17 PM »

I did a quick search on the rotor PN at RealOEM. The 90amp part x-refs with pretty much every e30 (and the early M5 & M6...good luck finding one of those).

The front cases are different, I'd say try a swap.

jdirty · « **Reply #6 on:** July 14, 2011, 08:11:58 PM »

thanks for the schooling DesktopDave. that really enlightened me. i was able to source an alternator from a 08/1990 325i from the yard that looked new! at first i popped the voltage regulator and the brushes were untouched. peeked the rotor and it looks new as well.. yanked it out. put the regulator back in.. dropped by several autozones to have it checked and it passed. all of them noted that it sounded a bit noisy though.. i just got back from my quest and will press onto the disassembly.

DesktopDave · « **Reply #7 on:** July 14, 2011, 08:48:14 PM »

Good going. It was all guesswork, although RealOEM makes stuff like this easy. You might want to repack the bearings with high-temp electrical safe grease, or get new ones. They're cheap - looks like BMA has the front one for $4.95. It's even an SKF. Likely you can find decent bearings on EBay too.

front is a grooved 47X17X14, BMW part 12311722979
rear is also grooved, but 32X12X10, BMW part 12311739203

Have a bearing press? Check out this vid, the guy really knows his stuff (and the music isn't that bad).

jdirty · « **Reply #8 on:** July 15, 2011, 02:10:10 AM »

you know what.. i couldn't get the housing bolts moving for the life of me. i ended up being lazy, put the 'like new' regulator in the original alternator, brought it to some autozones and had it tested, it passed. lol so i have a spare working alternator right now, which i scored for $33. lol i'm dealing with massive squeeling and screeching from the alternator though. haven't really dialed it in because it was getting dark out. i do work outdoors without any nearby electrical outlets. will get to it tomorrow.

the alternator bracket adjusts the belt tension right..?
is it all the way out? it doesn't seem to want to go all the way with me(lol).. or am i just being overly cautious with the tension..?
i noticed that when i try to make it extra tight.. the pulley seems to move towards the engine and opposite the direction of the alternator itself.

DesktopDave · « **Reply #9 on:** July 15, 2011, 06:41:56 AM »

Those Bosch alts are really tough little beasts. Do both of them have bad bearings? If the pulley is moving inside the alt housing you'll have to replace one or both bearings. It shouldn't move laterally at all, only spin.

Yep, the bracket adjusts the tension. Might just be a loose belt - it'll definitely make a lot of noise if it's loose or if the rubber on the belt was scorched it might not be gripping the pulley. Since that little adjuster gear wheel tends to strip I use a short prybar to pull the alt out and stretch the belt tightly. Don't worry about breaking it, those belts are very strong. I usually tighten the belt a good deal...when it's adjusted correctly I can deflect it a little (only about 1/2") in the middle of the longest span pressing hard with my thumb.

New belts will stretch, so make sure you check them again in a few weeks.

jdirty · « **Reply #10 on:** July 16, 2011, 06:16:24 PM »

the noise is gone now. i wasn't able to fully extend the alternator bracket but maybe 7/8 of the way out. belt had around 1/4"+/- slack. sound was there for a bit, almost sounded like metal hitting metal at one point.. then it went away. started the car back up and it was completely gone.
then i noticed that my brake lights were on. realized it was only the brake switch near the pedal stuck. got that sorted out.. so now that the car was running and charging again..
it was on to bleeding my cooling system.
massive coolant coming out of sparkplug #2. temp at 3/4.

cracked head for sure. sigh.

DesktopDave · « **Reply #11 on:** July 16, 2011, 06:37:11 PM »

Gah. That sucks. Hopefully it's only a head gasket.

jdirty · « **Reply #12 on:** July 16, 2011, 09:13:10 PM »

that's the thing.. i just replaced the headgasket. i'll bet it's a hairline crack opening up under pressure. couldn't get the head pressure tested atthe time of the hg replacement.