theiceman

take the fan belt off and start the car and see if it makes the noise .. your gonna know pretty quick .. also if you are suspecting clearance sand the edge of the blades ... you dont see them anyway ..

jakeflyer

If you want to isolate the noise, and you think it may be fan unit related, why not pull the fan belt off (this will disable the fan and alternator) and run the engine for a short time. If the engine is cold, I think you could fun it for a few minutes without harm,

Pull the nut off and see how the spacers are placed, Leave the nut, spacers and pulley halves off when you run it.

Follow the procedure for making sure the belt is correctly adjusted using the spacers.

jakeflyer

ice man----- seems like we had the same idea at the same time--- you beat me to the post

Brett San Diego

You can run the engine again for a minute with the belt off to see if the sound goes away.

Brett

Bkresse

Guys, I really appreciate everyone's feedback.

I've tried and considered each and every one of the suggestions. Starting with determining whether the fan and the housing were interacting anyway.

I pulled everything apart and found there to be appropriate clearance all the way around, but just in case I sanded the inside of the housing smooth. The clearance and operation was verified by a classic Porsche repair shop here in town. I ended up taking the complete assembly out and taking it to the shop just so that they can visually inspect all the components. They couldn't find any issues with the alternator, the fan, or the housing operation.

I did find a scope and positioned it around the engine to find the source of the sound. The sound is clearly coming from the fan housing area. Specifically the top center of the housing. to verify, I removed the fan belt and started the engine. The engine ran for a minute or two with no noise. I can say with almost certain assurance that the issue is isolated to the fan housing assembly. This too was verified by the Porsche shop as I took the car to them, again, and ran it for a while so they could investigated the source of the issue. They adjusted the fan belt tension; however: never identified or eliminated the noise either.

Next, I took all the components apart and investigated them with a fine tooth comb. I found that the plastic cover that protects the back of the alternator has two metal blades attached to it. One of these blades was loose while the other seem to be touching the housing. The blade touching the housing initially seemed like the most probable cause of the problem. In fact, I was so sure that this was the problem that I bent the thin metal fan blade back a little and then put the entire assembly back together; only to find out that the noise was still there. So then I remove the assembly, once again, and found the loose blade on the plastic cover, i riveted it back in place tightly and then reassembled and installed the assembly.

I still have the noise.

I'm beginning to believe that it just has to be the new alternator. The parts guy is telling me that in 30 years he has not seen bearings go bad in a Bosch alternator in two instances like this. Remember, the first alternator was only six weeks old and this one I just installed.

Clearly they're reluctant to throw parts at this problem; however, i just can't believe there's anything left to discover.

ivangene

I really dont know if it can be done (or would be a good idea) but you seen resourceful...

any chance of making a stack of washers on the ALT that represent the fan...remove the fan, install the pulley and run it???

my other thought is alignment of the fan belt itself....may be some angle from improperly seated fan housing, wrong pulley, bad pulley.... IDK

lastly...dont over tighten the fan strap....try loosening it up a tad....or tightening it a tad....

oldskewel

Isn't the fan half of the pulley, making this impossible?

It sounds like you're not 100% sure that it is due to fan-to-housing contact, so I'd recommend answering that definitively as a first step. Perhaps the easiest way would be to carefully inspect the housing for scrapes. You might even have red paint there to make it easy. Then to see if the potential contact spot is still making contact, you could write over it with a Sharpie (or equivalent - I remember when I used to work in a machine shop, we used this special blue liquid called Dykem for this sort of thing - probably better than a Sharpie because it was designed to form a thin layer that would easily be scraped away if touched). Run the engine, and after hearing the noise, inspect the spot. If contact was made,
the mark you made should show evidence of it.

Ed's recommendation to sand the paint off the ends of the fan blades makes a lot of sense, regardless of what you find here.

rusnak

Go back and re-read my last post, and try a different brand of alternator belt.

Brett San Diego

Yes, but one could spin up the fan on the alternator shaft without installing it in the housing to see if the noise is there without the housing. Maybe rig up a coupling to a drill to spin it.

Would a cracked housing allow deflection of the alternator mount under tension by the belt? But, I assume a support cracked all the way through would be readily noticed...

Brett

rusnak

When the fan gets some wear around the center hole, a belt that does not fit right can allow deflection, (causing the fan to clunk against the alternator washer or c-clip) even though there is proper tension. It is best to stick with belts that fit properly. The Continental Rubber belt fits the best, although I found a belt from Car Quest fit well too. The factory Porsche belts are spotty. The British made Opti belt is a POS.

theiceman

Rus is right i have experienced this . remember a few years ago I was eating belts ? i found some belts did make noise when they hit .. i assumed it was more mechanical though.This one i must admit is pretty interesting .

Bkresse

ivangene, I like where you're going because I'm still very suspicious about this being the new alternator. Problem is, I can't run it with the belt as described by oldskewel. I'm looking into doing something like Brett San Diego mentioned; however, I haven't quite figured out how I am going to rig this up yet. I was thinking that if I could, I would be able to investigate two issues. One: *I could run it with the fan in place and then two: I can run it without the fan removed.

Per rusnak, the first thing I'm going to do before I get to that experiment; *I'm going to get a new belt and see if that changes anything at all.

As far as the clearance between the fan in the housing, I'm pretty sure based on several observations that this clearance is sufficient. I was concerned that when I painted the housing I may have created the issue with the fan clarence, but since then I've remove the paint and smooth the area and I believe I've eliminated that possibility.

Also, I should mention that while I had all the components apart the Porsche mechanic and I investigated the integrity of the fan and then the housing. I was happy that both of these components seem to be okay. As I've been told they're difficult to come by and very expensive.

Last thing, rusnak, you mentioned an alternator washer and c-clip. I'm about 100% sure that I did not have a c-clip to support that washer. And I don't recall whether there was c-clip there or not. I'm thinking there was not as I remember moving that washer back and forth on the shaft trying to decide whether or not I should install it. Of course I did install the fan using the washer; however, I did not apply a c-clip in that position. If there is indeed a c-clip required, that could possibly be an issue.

Bkresse

I can't get a contitech (contenental) belt today. Any opinion on the Gates brand? I'm told it's a premium belt but I have no experience in the area of belt dynamics or quality.

rusnak

A pic of the alternator might help. Try without the washer. The fan needs to bottom out against something. I've always seen a clip on the alternator below the woodruff key. I've used Gates belts too with good effect. If it does not fit then return it.

Ed Hughes

If it does not fit, you must acquit!

I can't remember a "c clip" in my assembly, but then again, I don't remember a lot of things I should. I'm kinda focused on enhancing a 993 suspension right now.

PET doesn't show anything like that, as far as I can see. Shims, pulley 1/2, shims, fastener. Isn't the shaft shaped to fit the hole of the pulley 1/2?

Make sure it is ROCK SOLID without the belt on. No Wobble, and perfectly aligned with the crank pulley. That "should" take some of the variable out. Then, with belt installed and engine running-any wobble at all?