Finding fan/housing noise

NorthGaRob · 01-23-2011, 01:46 PM

I had to replace the alternator in my 1983 911SC. At first it seemed like this was the first thing that I have ever fixed on this car that was easier than a similar repair on my old truck, given that the alternator is so much more conveniently located.

However, after getting the new alternator back in the fan housing, I cannot get it to spin without making a grinding noise. Strangely, if I hold it up to a light I can see that there is a gap between the ends of all of the fan blades and the housing, but when I give it a spin with my hand, there is a grinding sound and it feels like it is grinding against the inside of the housing, but it looks like the fan is not contacting the insides of the housing.

I am really perplexed and would really appreciate any comments or suggestions that you guys might have.

As a potential aside, the new alternator came with what looks to be some sort of spacer (like a thick washer) but no details as to what it might be for. Any ideas about that would be greatly appreciated as well.

Thanks very much in advance.

Rob
North Georgia
'83 911SC

steely · 01-23-2011, 02:43 PM

Rob, I think you may have to take it out again and inspect.
Having said that I have a couple of questions: is the ALT back in the car under load from the belt, or does it grind in the housing when on a bench?
If in the car, can you remove the belt and see if it makes a noise?
Move ALT and housing to a bench and test? Did you happen to test spin the ALT before installation?

Or pop the fan and check for scuffing? Sorry no other ideas come to mind.
Good luck.

Flat6pac · 01-23-2011, 06:01 PM

Make sure there is a thrust washer behind the keyway to keep the fan off the alternator.
Bruce

NorthGaRob · 01-24-2011, 03:03 AM

steely - It was spinning freely when I first put it in but once I installed the housing/fan/alternator in the car and put the belt back on, it was grinding.

I think that Flat6pac is on to something. The new alternator came with a very thick spacer/washer but I was unsure where it was needed and did not use it. Now it sounds like I needed to put that on the alternator shaft before putting the fan on it. It makes sense, I guess that the scraping is the inside of the fan rubbing against the outside of the alternator. When I get home from work tonight I will try that out.

One more thing: my car is lacking the plastic air director that the shop manual says should be covering the back side of the alternator where the wires attach. Given that this has been this way for the full 6 years that I have had this car, is that a required part? Can I live without it?

Thanks for the replies, guys.

Rob
'83 911SC

Flat6pac · 01-24-2011, 04:17 AM

Youre going to cook the #1 and #2 cylinders because that extension directs cooling air to the 2 cylinders. You need it..
Bruce

NorthGaRob · 01-24-2011, 10:41 AM

Thanks for the advice.

Any idea what the part name is for that plastic air director that covers the back side of the alternator? I am trying to see if this site carries it but cannot seem to find it.

Rob

steely · 01-24-2011, 06:16 PM

Rob,
am just seeing your replies - sounds like you found the cause I see (washer).
As for the item, it's 91110605501 for my '87. Sorry I don't know your PN. It is called the hub extension, or fan housing extension, or air diverter. There is another name that escapes me. These get fragile with age and the thin flange breaks off making them difficult to re-attach to the ALT. Might explain what happened to your original.

Maybe you can use my PN to see if you can find an earlier one for your 83, but they're dear - like $95. You might try getting one from a dis-assembler.

Do you have the parts catalog from Porsche (PET)? If you do a search here, I am sure you'll find a link to the Porsche site that offers them up as pdf files for free - very handy. The PET pdf is searchable - note that they call the alternator a generator, and the housing extension is shown with the housing (not the alternator) btw.

hth

Flat6pac · 01-24-2011, 06:19 PM

SC number from the pet is 911.106.033.05

Bkresse · 11-08-2011, 08:03 AM

I was wondering if the Shim / Thick Flat Washer ended up being the problem?

I just replaced a bad alternator and a similar washer was included with the new Bosch Alternator. The alternator that I took off didn't have this washer in place, but I left the washer in place on the new alternator shaft anyway. I saw no reference in the Bentley manual to do so; however, it seemed to make sense to leave it on the shaft, so I did.

My problem is that even after a straight forward and seemingly successful alternator installation I have a new noise coming from the general area.

The noise is intermittent and erratic, somewhat dull as if something was rubbing/interacting with a tin plate. Not harsh or alarming, but it clearly shouldn't be making the noise at all. It comes and goes every 30 seconds or so but hasn't stopped yet.

I removed the A/C belt and loosened the fan belt by one shim to see if noise was tension related. While I might say the noise seemed less apparent, it still exist. I then tried to think of anything that may have been different, hence the washer question. I guess I was hoping that the washer might be the source of the noise if it wasn't supposed to be there. But after reading this thread, maybe it should be there and my problem lies somewhere else.

Any suggestions?

Thanks in advance!

NorthGaRob · 11-08-2011, 08:16 AM

In my case, that did it, but in my case I also had to get a new housing for the fan as mine was cracked. But once I had replaced the housing the noise was coming from the fan being too low in that housing, so I had to put that thrust washer in there.

Then I had continuing problems with the new alternator actually working because a wire and connector got contacted by the housing. I had to bend it out of the way and put some heat shrink around it. Finally it worked.

Bkresse · 11-08-2011, 08:30 AM

I was surprised that the fan wasn't touching the housing at all after installation. You know how little clearance there is on these things it almost seems impossible that the fan wouldn't touch the housing. But luckily after installation of the fan, and before adding the belt, the fan rotated cleanly. I thought I was home free.

I'm happy your car's running properly after all you had to do. As they say, one thing always leads to another.