Fan is hittin on 77 911

Argeo · 02-17-2007, 05:12 AM

The fan is rubbing the housing when it is spinning and has been for a while. The contact is not heavy but noticably if you really listen for it. What typically causes this? The alternator is relatively new, maybe 6-7K on it. The housing is the original.

I do not have any over heating issues. I am surprised after drving like this for a while that one of the two pieces would have wore down. Anyways, probably time to fix.

Any opinions?

David

grim77911S · 02-17-2007, 06:29 AM

Try loosening the alternator stap, to tight and the fan will rub.

ghnat · ghnat's Garage

If you can hear the rubbing I would suggest taking the whole assembly out of the car and inspect the housing for cracks. First thing I thought of was worn alternator until you mentioned how new it was. My housing had, oh about 4 cracks in it. There was no rubbing, but it would be only a matter of time. You could buy new Aluminum one or try to get the mag one welded. I have heard about some issues with the aluminum ones, but I think someone with more knowledge will chime in.

kach22i · kach22i's Garage

I'm embarssed to say that I know the car will still run with the fan housing improperly installed. Look very closely at the bottom timing notch. I had to redo mine after the alternator installation, took some determination to set right.

Formerly Steve Wilkinson · 02-17-2007, 07:27 AM

I would be surprised if it's possible to weld magnesium.

kach22i · kach22i's Garage

Picture of bell lip over bottom pulley, not behind it.............do not do this!!!!!

The fan noise might be becuase of this, although you would be eating belts very quickly.

Alternator Ground Strap

Argeo · 02-17-2007, 06:01 PM

I'll try and loosen the belt using an extra shim. Seems like a great place to start.

Thanks,

David

dweymer · dweymer's Garage

I had the same issue, and found my bolts that hold the air guide on , and hold the alt in the housing were loose on top. May want to double check them.

William930t · 02-18-2007, 05:22 AM

If you find the alternator mounting bolts are loose, you are lucky.

My fan rubbing was caused by cracks in the magnesium housing, specifically at the alternator ring support braces. Magnesium degrades over time, especially in humid climates. It is a good idea to pull the whole assembly and inspect for cracks/warps. Depending on your model, there are OK quality OEM housings available from various used parts suppliers. Vertex makes an all aluminum one but may take some force to fit.

Let us know what you find.

Shaun @ Tru6 · 02-18-2007, 05:53 AM

Quote:

Originally posted by Formerly Steve Wilkinson
I would be surprised if it's possible to weld magnesium.

consider yourself surprised. Mg can be TIG and arc welded.

hi David.

mb911 · mb911's Garage

Quote:

Originally posted by Formerly Steve Wilkinson
I would be surprised if it's possible to weld magnesium.

what! come on we do this every semester for our students to show them it is indeed very possible and works very well.. I have fixed many of fan blades and a couple of housings. that said once the housings crack they typically have a bunch of cracks which don't make it worth while

Formerly Steve Wilkinson · 02-18-2007, 08:41 AM

That's interesting. I remember watching an F2G Corsair crash with its magnesium firewall on fire simply from the heat of the burning gasoline. So yeah, consider me surprised.

rlane · 02-18-2007, 09:55 AM

Here is a fairly readable update from the FAA that touches on the issue, if small bits (dust, bits, strips) get heated to melting point watch out. This was always a great demo in HS chemistry lab with VERY thin strips of Mg

mb911 · mb911's Garage

Quote:

Originally posted by Formerly Steve Wilkinson
That's interesting. I remember watching an F2G Corsair crash with its magnesium firewall on fire simply from the heat of the burning gasoline. So yeah, consider me surprised.

remember we are using an inert gas (argon) so there is no oxygen present to allow it to burn just melt.. the dust however now thats different

defcon65 · 02-20-2007, 12:14 PM

Quote:

Originally posted by rlane
Here is a fairly readable update from the FAA that touches on the issue, if small bits (dust, bits, strips) get heated to melting point watch out. This was always a great demo in HS chemistry lab with VERY thin strips of Mg

Can't be as impressive as dropping a tiny bit of sodium wire into a bucket of water...

Make sure the alt shaft washer behind the fan is on the correct way so the little flange sticks out, mine was rubbing on the housing because this was reversed...

Regards,