Scraping Fan Housing

mca · 10-12-2007, 06:24 AM

I have some very noticeable scrapes on my fan housing right at the bottom - dead on with the z mark. I colored them in with permanent black marker in order to determine if it was past damage. I kept checking for a few consecutive days and the marker had not been scuffed off. Then, I checked about a week later and the marker had been scuffed off.

From reading past posts, it seems as though the following could be possible causes:

1) Chipped fan blades cause unbalanced fan - I have 3 chipped blades. Really? Can these really become THAT unbalanced?
2) Worn out alternator bearings
3) Cracked fan housing
4) Bent pulley shaft

When I remove the fan belt and hand spin the pulley, I can't hear any significant grinding noises coming from the alternator bearings. The alternator only has 22k on it. Can bearings wear out that fast? Also, when I hand spin the pulley, should it be compelety quite? I can hear a little, very very very faint grumbling ... but not significant at all.

Today I went ahead and loosened my fan belt by swapping 1 shim from the outside to the inside. Can a overtightened fan belt result in scraping?

Thanks for any and all help. I have a new fan coming but I don't want to install it if something is out of whack - last thing I want to do is chip a $200 used fan.

wachuko · wachuko's Garage

Most likely a cracked fan housing... pretty common with these magnesium housings... only option is to replace it ( you can try to weld... but best to just replace...)

I just went through the same situation... alternator was fine...

See the lower left corner in the photo...

And when I removed it there were additional cracks around the housing...

Here is my thread on that: Alternator issues

euro911sc · euro911sc's Garage

Also, if you tighten the fan housing strap too much your housing strays from concentric circular to ovular and the fan blades will scrap the inside of the fan housing... Your engine will literally scream out when this happens... don't ask how I know...

Best regards,

Michael

mca · 10-16-2007, 05:24 PM

Quote:

Originally Posted by euro911sc

Also, if you tighten the fan housing strap too much your housing strays from concentric circular to ovular and the fan blades will scrap the inside of the fan housing... Your engine will literally scream out when this happens... don't ask how I know...

Best regards,

Michael

Thanks a ton ... both of you.

I pulled my fan housing out in order to get a look at my cylinder heads as I am chasing a temp problem. The alternator strap WAS quite tight. I don't have any cracks on the housing. So it was probably due to the strap.

Also, the fan spins freely with no drag ... but every so often I can hear a little bit of faint grinding ... I mean FAINT. The alternator only has 25K on it. How long do these usually last?

Nutmeg911 · 10-16-2007, 06:50 PM

A properly rebuilt alternator should last longer than that I would say at least 50,000, but my ford Focus Alternator only lasted to about 30,000 and the original alternator in my Mustang has 97,800 on it , I pulled my 911 alternator at 97,000 ,but was previously rebuilt because it had Chinese bearings in it but I don't know when that was. So maybe from this reply I probably did'nt answer your question.

island911 · 10-17-2007, 12:14 AM

2) Worn out alternator bearings

...is my bet. Bearings are load sensitive --over load them (too tight belt) and they will wear prematurely.

Try lifting & spinning the fan. (belt off) If it no longer scrapes the bottom, then the bearings are sloppy.

jester911 · jester911's Garage

I had this problem. I was told by a shop that I needed a new alternator. After close inspection I realized some debris got trapped in between the fan and housing. It caused a burr to stand up on the housing which would sometimes touch the fan blade.

I used course sandpaper and sanded down the area and went to finer sandpaper to make it smooth. This has been over 5 years ago and it still going strong. Oh and I don't go back to that shop any longer. YMMV

mca · 10-17-2007, 05:30 AM

Do worn alternator bearings get louder and louder with more wear?

I have the alternator out of the housing unit. If I spin it, should there be ZERO noise?

island911 · 10-17-2007, 08:23 AM

Worn bearings make noise. THe key, for you, is to check for slop. ---rock the pulley up & down, and you should be able to feel the slop. If no slop, do as Jerry suggests above.

Won · 10-17-2007, 09:15 AM

I had the same problem; simply tightening the little nuts that hold the alternator on to the fan housing did the trick for me.

rusnak · 10-17-2007, 04:37 PM

I doubt the problem is the alternator bearing or shaft if the fan is scraping only at the bottom of the fan shroud.

Try tightening the alternator nuts opposite of the scraping area. This will pull the fan away from the shroud and will stop the scraping. Seriously, try it and it should work.

Paul Crowther · 10-18-2007, 03:46 PM

Maybe the alternator is not properly aligned in the shroud. When pressing it onto the bolts, it must be pressed to the flange below or it won't be true inside the shroud, cuasing uneven spin.
Paul

3.2Carrera · 3.2Carrera's Garage

i am currently having the same problem w/ my car, but it only scraps( makes a noise) when i use the lights or the A/C. I just had the alternator bearing replaced, but i have a new pulley and my fan and housing was just repainted, I dont think its the bearing , i am going to take mine apart on tuesdays, i will keep you posted, i think, it may just have to be replaced. any other suggestions???