Alternator Help
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Joined: Jan 2002
Posts: 51
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From: Portland,OR
Alternator Help
Just back from more repairs. Engine out, added seals to the cam shafts where they meet the housing to prevent leakage. It was unsucessful. I do not believe that they know where it is actually leaking from, or that the oil flow is blanked-off somwhere in the engine and causing the oil to push through the path of least resistance in that particular area. I'm no mechanical engineer though.
My new problem since the car has been back, besides the oil leaking, is that the Alternator belt was squealing/slipping on take off. I check the tension on the belt by hand and it seemed to be plenty adequate, although while running I noticed that the belt was wobbling heavily on the left side only. Today I smelled the belt burning as I took off, then the slippage stopped. A few more takeoffs and, smoke was bellowing from the heating vents. I stopped the car and checked the engine to find the alternator belt was bubbling, but still on. While I was watching it bubble against the pulley, the belt spontaneously snapped in half. I managed to pull the hot belt from the pulley, and make it home.
Once home, Upon inspection, I was able to freely rotate the alternator shaft, but I noticed that it had a very slight wobble to it as it rotated. It does not feel "loose".
Please tell me your thoughts on this phenomena. Possibly a cracking shaft, as I've read about. Did the mechanic possibly bend the shaft upon removal/installation. I've never had any belt noise whatsoever before this latest repair??
P.S. I have contacted Porsche about my horrible experience at the shop.
Thanks as always.
Daniel
My new problem since the car has been back, besides the oil leaking, is that the Alternator belt was squealing/slipping on take off. I check the tension on the belt by hand and it seemed to be plenty adequate, although while running I noticed that the belt was wobbling heavily on the left side only. Today I smelled the belt burning as I took off, then the slippage stopped. A few more takeoffs and, smoke was bellowing from the heating vents. I stopped the car and checked the engine to find the alternator belt was bubbling, but still on. While I was watching it bubble against the pulley, the belt spontaneously snapped in half. I managed to pull the hot belt from the pulley, and make it home.
Once home, Upon inspection, I was able to freely rotate the alternator shaft, but I noticed that it had a very slight wobble to it as it rotated. It does not feel "loose".
Please tell me your thoughts on this phenomena. Possibly a cracking shaft, as I've read about. Did the mechanic possibly bend the shaft upon removal/installation. I've never had any belt noise whatsoever before this latest repair??
P.S. I have contacted Porsche about my horrible experience at the shop.
Thanks as always.
Daniel
Instructor
Joined: Oct 2002
Posts: 155
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Did the shop put in a new belt? When you replace the belt, you have to re-allocate the shims appropriately. A new belt is nominally shorter than an older belt and if the shims are not right, you might get too much tension and snap it.
Race Car
Joined: May 2003
Posts: 4,241
Likes: 103
From: SoCal
The 964/993 alt./fan assembly should be monitored for belt tension and
bearings, i.e there are two (fan also), more than 3.2 or 996 because of the
alt. shaft length and leverage placed on it by the belts. Neither the alt. nor
fan bearing should exceed 100K miles. Also, excessive belts tension over
stresses the shaft and the bearings (extra bearing load causes heat and
damages bearings).
Have Fun
Loren
'88 3.2
bearings, i.e there are two (fan also), more than 3.2 or 996 because of the
alt. shaft length and leverage placed on it by the belts. Neither the alt. nor
fan bearing should exceed 100K miles. Also, excessive belts tension over
stresses the shaft and the bearings (extra bearing load causes heat and
damages bearings).
Have Fun
Loren
'88 3.2
Addict
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Joined: Jul 2003
Posts: 2,577
Likes: 52
From: Atlanta
Belt movement on the slack side tells me the belt is not sufficiently tight. Squealing on take-off is cause by the extreme torque required by the alternator as it attempts to charge the battery and pull any electrical accessories that are running. Your load may have been greater that normal, as the battery was probably low after an idle period.
You obviously need a new belt, and you need to get to the bottom of the problem. A dial indicator on the alternator shaft will show if the shaft is bent. If it is not, , cleaning the melted rubber from the pulleys and a careful installation of a new belt is all that you need. If the shaft is bent, a new alternator is in order. I don't think it can be straightened in-situ.
Good luck
You obviously need a new belt, and you need to get to the bottom of the problem. A dial indicator on the alternator shaft will show if the shaft is bent. If it is not, , cleaning the melted rubber from the pulleys and a careful installation of a new belt is all that you need. If the shaft is bent, a new alternator is in order. I don't think it can be straightened in-situ.
Good luck
Race Car
Joined: Jun 2001
Posts: 3,706
Likes: 10
From: Virginia Beach, Va.
A couple things here, when you were turning the alternator shaft, are you sure it was the alternator shaft and not the fan pulley?? I just want to make sure that you realize that one belt turns the fan, the other turns the alternator at a different speed.
With that in mind, does it appear the shop had your pulley assembly apart? ...are there fresh marks in the "ribe" at the end of the shaft, etc.
It sounds like they either just got the belt back on too loose or apparently screwed something up.
ALWAYS keep ALL the shims on the shaft when adjusting the inner belt, the one for the fan, if it's too loose, take a shim out from between those pulley halves and add the one you took out to the outside of the front pulley half, if to tight, vice-versa.
As the outer pulley turns the alternator shaft, keep in mind that this is a separate adjustment, with shims as well.
I had a friend with an SC years ago that would pull a shim out to tighten the belt and put the shim in some "parts collection" somewhere that he would never find later...on an SC this would also make so the large nut on the alternator/fan shaft (combined on those cars) would bottom out before it actually had everything "snugged up".
This is what would egg out the fan spindles and cause owners to purchase new 11blade fans.
I don't believe (from memory, trying to picture the assembly) that this would affect the 964 setup the same, but thought I'd bring the 911SC assembly up because it was somewhat related.
If both of your shafts seem to rotate okay, replace the belt, adjusting the shims so they are both snug. Also ensure your alternator housing clamp is snug, there is a torque rating for it, it's pretty low...escapes me at the moment. (I'm not at home with all my notes)
Let us know how your alternator escapades turn out.
With that in mind, does it appear the shop had your pulley assembly apart? ...are there fresh marks in the "ribe" at the end of the shaft, etc.
It sounds like they either just got the belt back on too loose or apparently screwed something up.
ALWAYS keep ALL the shims on the shaft when adjusting the inner belt, the one for the fan, if it's too loose, take a shim out from between those pulley halves and add the one you took out to the outside of the front pulley half, if to tight, vice-versa.
As the outer pulley turns the alternator shaft, keep in mind that this is a separate adjustment, with shims as well.
I had a friend with an SC years ago that would pull a shim out to tighten the belt and put the shim in some "parts collection" somewhere that he would never find later...on an SC this would also make so the large nut on the alternator/fan shaft (combined on those cars) would bottom out before it actually had everything "snugged up".
This is what would egg out the fan spindles and cause owners to purchase new 11blade fans.
I don't believe (from memory, trying to picture the assembly) that this would affect the 964 setup the same, but thought I'd bring the 911SC assembly up because it was somewhat related.
If both of your shafts seem to rotate okay, replace the belt, adjusting the shims so they are both snug. Also ensure your alternator housing clamp is snug, there is a torque rating for it, it's pretty low...escapes me at the moment. (I'm not at home with all my notes)
Let us know how your alternator escapades turn out.
Thread Starter
Advanced
Joined: Jan 2002
Posts: 51
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From: Portland,OR
Thank you very much for the helpful reply Jeff. I've been reading all my literature on how the shafts, fans, and pulleys line up, and I'm about to tackle the project. I had to order the special shaft wrench to get the nut off the alternator.
Is part # VW 202 (pulley puller) necessary? or, can I use another more generic puller? or, maybe I will not need a puller at all. I do know that the shop replaced the belts within the past year.
Thanks again
Daniel
Is part # VW 202 (pulley puller) necessary? or, can I use another more generic puller? or, maybe I will not need a puller at all. I do know that the shop replaced the belts within the past year.
Thanks again
Daniel
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Burning Brakes
Joined: Oct 2003
Posts: 788
Likes: 27
From: Norfolk, England
I had this problem after Porsche fitted a new alternator (they broke my original taking it off!)
Afterwards, it quickly went through three or four belts before they stopped it squealing and smoking. Drove me nuts how a £5 belt can stop a £50,000 car!
Anyway, they eventually cleaned everything up and stuck another belt on which did the trick.
Good luck
Afterwards, it quickly went through three or four belts before they stopped it squealing and smoking. Drove me nuts how a £5 belt can stop a £50,000 car!
Anyway, they eventually cleaned everything up and stuck another belt on which did the trick.
Good luck
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