Alternator noise revisited

Kurt B · 05-24-2005, 10:53 AM

Sorry to belabor the issue, but if there is a 'grinding' noise at low RPMS from the alternator area, what would be grinding?
I don't see the fan rubbing against the housing, and although the fan belt isn't real tight, I don't seem to be able to move the fan (so I don't see any play).

Do the bearnings 'grind' as they turn when they begin to wear out?

TerryH · TerryH's Garage

Remove the belt momentarily and see if the noise goes away. Bearing noise is usually the first sign of mechanical failure on the alt.

RoninLB · 05-24-2005, 09:59 PM

so you checked that the fan wasn't rubbing the fan shroud. It may be hard to see. Alt bearing noise is different from the fan rubbing noise. maybe remove the belt and check alt bearing play?

the pully hub may be beat?

Kurt B · 05-24-2005, 10:03 PM

see...the guy at TRE (where I took my car to pass smog and had em adjust the valves which really made a huge difference in the car by the way) said the fan was probably rubbing a bit..but I figured "how..." but ronin you could be right. As the first guy said, I'm gonna have to pull it and run it for a few and see if it goes away, which is the plan...

RoninLB · 05-24-2005, 10:16 PM

Quote:

Originally posted by Kurt B

, I'm gonna have to pull it and run it for a few and see if it goes away, which is the plan...

so the noise stops.. so you gotta find the rubbing.

You might get a good feel where it may be rubbing by hand turning the fan?

also sometimes the previous alternator install leaves the fan mis-aligned and bearing wear eventually caused fan rub.

If the fan hub is beat it can usually be patched up or you will need a new fan. If everything is tight and you can't see or feel rubbing I might consider examining the fan hub. It'll be the end of the somewhat rectangular hub fitting that gets rounded. It's a long shot but worthy of a note.

Kurt B · 05-24-2005, 10:30 PM

Great advice...I had a devil of a time getting new alternator installed. Installed it wrong and all this stuff..was not fun (but it looked so easy)....it took a year for it to start rubbing....and it's gotten progressively more noticeable. Okay, I'll try those out and post the results thanks!

Mysterytrain · 11:49 AM

Intersting..I've been trying to track down a noise that is not grinding or scraping..more like a hollow tone. I think I read somewhere that the plastic shroud on some cars resonate. Anyone else experience this and have a cure??

cstreit · cstreit's Garage

If you don't get the 6 small bolts on the back of the alternator tourqued evenly, it can get the whole assembly cocked in the shroud enough for the fan to rub...

Crowbob · 05-25-2005, 05:41 AM

Cstreit:

So what is the tourque value for those bolts?

Jim

Mysterytrain · 11:48 AM

I'm not hearing a rub and I'm not seeing evidence of rubbing on the fan housing. What I hear sounds like a hollow plastic or cardboard tube..something like the tone you get when you blow into a large soda bottle or a jug...you guys remember jug bands.

TerryH · TerryH's Garage

The top of my motor had that hollow sound too. Once I removed the fan belt and ran the motor for a moment, it was obvious the alt/fan was the noisemaker.

When I spun my fan by hand with the belt removed, it was apparent the bearings were bad. There was a clicking type sound. Be sure to spin the fan only in the normal direction to get an accurate sound and not break brushes. There won't be load on the bearings without the belt, so any noise you hear is probably a bad noise that would only be magnified under load.

Pulley alignment, belt tension and condition are other things to look at along with possible contact by the fan inside the housing.

Superman · 05-25-2005, 08:31 AM

Yep, remove the belt and run the engine very very briefly. Spin the alternator by hand. It should be smooth as butter. Anything less means a bad bearing. When under load and spinning at regular speeds, worn bearings rumble and growl. Alernator bearings usually make more of a rumbling sound, and wheel bearings growl more, but it's really the same noise. Also, you can use a stick or long screwdriver against your ear and against a part to listen to what's going on with that part. Unfortunately, the alternator is not accessible but the fan shroud is, and the alternator is bolted to that. Put your hair in a pony tail, don't wear loose clothing and be very careful. Or better yet, shave your head and work on your car in the nude.

Kurt B · 05-25-2005, 08:39 AM

LOL

Mysterytrain · 05-25-2005, 10:16 AM

Very true on the safety issues (you what is really bad..hooded sweatshirts with those damn dangling strings)
Anyway, in my case I have a new alternator with 3K on it and the new engine. I doubt its the bearings. The pulley alignment looks right on? I read in UP fixin' years ago that some housings did resonate.

WERK I · WERK I's Garage

Quote:

Originally posted by Mysterytrain
Anyway, in my case I have a new alternator with 3K on it and the new engine. I doubt its the bearings.

If it's rebuilt replacement unit, don't bet on it. I have an alternator(rebuilt/exchange) with less than 5K miles on it. Guess what?! Bad bearings....I hate replacing alternators on these cars.

Mysterytrain · 11:54 AM

I have to laugh. During my rebuild my mechanic asked me..what do you want to do with the starter and alternator since they are both 27years old? Yeah, well I guess I should replace them both as long as we are in there. So I bought a new alt and a rebuilt starter..even though my old parts never gave me troubles. The starter hasn't fully engaged 3 or 4 times and I'm praying the you are wrong about the alt. Although now that I think about it I have always had this noise back there. So it might be some sort of odd ball resonance. Occurs between 2 and 3K.

Kurt B · 05-30-2005, 10:34 AM

Wow. It appears as though this was caused by using the wrong fan belt of all things. I had a Porsche one handy, and I compared it to the one I had on there I had gotten some place.

Noticed I guess, that these are completely different. Porsche is thicker, not ribbed and actually shorter.

After taking fan/alternator out yesterday, I was at a loss as to what could be going wrong there.

For the hell of it, I put the Porsche one on. And then I remembered how hard it was to get a new Porsche fan belt on (in comparison to the other one I had).
Got it on there, torqued it. And the grinding is completely gone.

I should say, the other one was looseish, even though I had it about as tight as it would go. I guess the other one worked for a few months before it became useless. Usually when belts go bad in my experience they squeal if they're the right length to begin with. This one, when it got old simply stretched way out of spec while otherwise being in fairly good shape. Gotta chalk this up as another bozo experience. Wish I had tried this 4 months ago.

WERK I · WERK I's Garage

Quote:

Originally posted by Kurt B
Wow. It appears as though this was caused by using the wrong fan belt of all things. I had a Porsche one handy, and I compared it to the one I had on there I had gotten some place.

Noticed I guess, that these are completely different. Porsche is thicker, not ribbed and actually shorter.

Not ribbed....do you mean ribbed on the inside circumference of the belt? Ooooh, boy, mine is ribbed internally too, if that is the case.

Kurt B · 05-30-2005, 01:50 PM

Well, a pic is worth many words so here's the one I took off versus the Porsche one installed.
It is not just a matter of shadow. There no ribbing on the interior circumference of the Porsche belt.

Pat Crellin · 05-30-2005, 04:41 PM

I have a low, kinda hollow rumble noise that does not change with the RPM's. My mechanic said I had 2 months left on the alternator. I took the alternator to a rebuild shop, sounded fine on the bench. Told him to rebuild it anyway.
Back in the car, smooth as butter. Same noise. Next time I was by the mechanic, I ask about the noise, he thinks it's still the alternator. It's not.
The shroud is tight and doesn't vibrate. I would like to know what it is. I kinda forgot about it untill I saw this thread. ????