Hello There! First I just wish to thank you all for such an amazing forum. I have been reading many discussions for some time now, but always been too shy to introduce myself or ask questions! Like all of us here, I love Porsche and have been fascinated by these cars since childhood particularly the 993; so finally the dream came true and a Black 993 came my way. I am a professional classical musician, so engineering and mechanics was nothing but a hobby in the absence of a better word, however you guys have giving me the courage to go over my expected limitations!

I have read and studied the following links about the engine cooling system:
https://rennlist.com/forums/911-foru...an-wobble.html
https://rennlist.com/forums/964-foru...n-bearing.html
https://rennlist.com/forums/964-foru...rnator-be.html
https://rennlist.com/forums/964-1989...n-removal.html

I hope I am not beating a dead horse with this questions and if I have missed something in the reading just let me know..

Is it possible that the fan inner pulley could get some how warped over the years so as to have some play when it seats in the fan hub and alternator shaft? Also, have any of you encountered the case where the fan is some how warped like not symmetrical, so when it spins is given the optical "illusion" that is wobbling, but does not hit the shroud not there is any markings on the shroud either?

The fan shows two superficial cracks near the center and the fan inner pulley does appears to have play when is not under the load of the belt.

(video 1.)
On the contrary, the alternator inner pulley does not at all have any play not even 1/2 a millimeter, it just seats in the shaft there tightly. What does this means? The fan spins freely, and the alternator does as well, no grinding sounds of any kind..

(video 2.)
Is my assumption correct?

I know there is something wrong there; the rattiling noise, see (Video 3.)
Maybe the fan hub? The fan is toasted too? And also the inner pulley? The alternator is only 2 and 1/2 years old. My goodness, perhaps the alternator too?

In the following link https://rennlist.com/forums/964-1989...n-removal.html , reenlister MarkD mentions that "if the fan wobbles in the shroud while spinning the alternator shaft, that means that the rear alternator bearing is gone bad." Could this be the culprit? How does the rear bearing of the alternator affect how the fan spins?

Although I think that the wobbling sound might come from the fan inner pulley vibration as it rotates in oddly ways together with the fan, I am not sure...this assumption might be wrong..

So in a nutshell, due to how those cracks in the fan, should I get a new fan? should I also replace then the fan hub and fan inner pulley? Also, the rear alternator bearing? Does that means new alternator? Is that it or is there anything else you guys see and or hear that a totally rookie like me is for sure missing? Thank you so much for your help!!

 

Don't get too excited yet, lets work through it.

Any play in pulleys without the belt installed and the nut tightened is normal - they need some clearance to be able to be assembled.

On the third video, if that slight rubbing noise is what you are concerned with, it could be the fan blades touching the shroud (although usually that is a squeakier sound). you can look for shiny or polished sections of the inside of the shroud to see if the fan has been touching.

IF the front bearing on the alternator is worn, it can cause the shaft to sag slightly under the load of the belts, and push the fan down slightly, so the contact point with the shroud can be at the bottom. If the bearing between the alternator and the fan is worn, it can have a similar effect, perhaps not as much.

There is variance in the castings for the fan blade, so the real check for out of round is the tips of the fan - they are machined accurate based on the hub of the fan - the runout is very small. You cannot use the side of the fan visually as a check, its a casting that has not been machined and it can show a slight wobble.

Small casting cracks are normal.

You said there is no slop in the fan at all?

If you are going to check for runout - do it with all the nuts bolted up to the pulleys are tightened up.

Cheers,

Mike

 

Could the noise in the third video be vibration induced rattle from a heat shield?
Not uncommon for the heat shield to weaken or rust through at a heat shield bolt and start rattling. Does a very slight increase in engine RPM change or eliminate the noise?
Something to look at would be all of the aluminum shields on / around the mufflers and catalytic converts.

 

Thank you so much for all the tips! Yeah, the Fan does not show any play or slope when I grab it with my hands and push and pull in all directions. I am going to check for runout with the pulleys bolted and tightened up. I am also going to look very carefully for marks on the bottom of the shroud. I guess, as the belts pull down on the pulleys it is not enough to assume the fan does not hit the shroud when the belts are not on the pulleys. It could still very well hit the shroud under the load of the belts. So I will go from here and report back!

 

Thank you BesidetheBox for your suggestions! I will look into the heat shield as well and will follow up with the RPM test and see if the rattling goes away.

 

If the alternator belt was installed with excessive tension, that could cause rapid bearing wear.

With the engine cold, start the car with no belts installed. Do not let the engine run longer than necessary...30 seconds should do. Do you still hear that same wobbling sound?

If not, then you have tracked it down to alternator bearings and/or fan hub bearing. You can then continue with the process of elimination.

 

The bearing can resonate at a particular or range of RPM.

A local 993er who was working on another 993 had a slight vibration that could be felt in the fan housing.

The fan hub bearing felt fine with smooth rotation and did not sound dry. Yet at RPM it went into resonance. Goes to show a hand rotation test is only good for the extremes; either the bearing is good or really gone.

A new fan hub bearing was installed; the issue was solved.

Of course this could apply to the alternator bearings as well.

 

Oh my goodness! Thank you so much all of you guys IXLR8, MikeJ and BesidestheBox for taking the time to help me with this! We have some awesome weather this weekend here in CT, so I am going to get in the garage and do all the tests you suggest and report back as soon as I am done!