Strange one this ... 993 Alternator belt
Discussion
Picked up my 993 from the local Indy on Saturday after brake work, drove her around 20 miles and then parked her up at home with no issues. Left her till this morning and needed to take her to work as my daily is playing up. Drove around 3/4s of a mile, smoke in the cabin, pulled over lifted the engine cover just as the alternator belt self destructed.
Now the weird thing is this. The day I was taking her in for work on the brakes, I started her up after a few days without use, drove 3/4s of a mile and the same thing happened in exactlly the same place, same time of day. So when she was in for further work I got them to replace the belt. I thought it strange for a belt to go as the old one had covered around 8K miles, but these things happen.
Now all the pullies had been checked, there's no play in them and they spin freely and are aligned. As I said I drove the car on Saturday afternoon with no issues, yet twice from starting from cold, the same distance at the same time of the morning I have now lost two belts, and both have broken, the only warning I had was that the belts started to squeel a few hundred metres before they broke.
Instant thought is it must be the alternator/bearings yet nothing seems amiss. Has anyone else come across this issue before and if so any idea why/what it is?
Confused of Evesham
Now the weird thing is this. The day I was taking her in for work on the brakes, I started her up after a few days without use, drove 3/4s of a mile and the same thing happened in exactlly the same place, same time of day. So when she was in for further work I got them to replace the belt. I thought it strange for a belt to go as the old one had covered around 8K miles, but these things happen.
Now all the pullies had been checked, there's no play in them and they spin freely and are aligned. As I said I drove the car on Saturday afternoon with no issues, yet twice from starting from cold, the same distance at the same time of the morning I have now lost two belts, and both have broken, the only warning I had was that the belts started to squeel a few hundred metres before they broke.
Instant thought is it must be the alternator/bearings yet nothing seems amiss. Has anyone else come across this issue before and if so any idea why/what it is?
Confused of Evesham
Orangecurry said:
Are you sure you have the correct belt? There are about seven to choose from.
And is the pulley the uprated one, or are you on the original?
Pretty sure yes as even the battery light came on within the dash. It's not the fan or ac belt. I had all the belts changed whilst it was at the Indy just for good practice. Same belt broke the 2nd time as the first did, the others were fine. And is the pulley the uprated one, or are you on the original?
Pully? Updated one? What's all that about then .......
If it was already the wrong belt, and they looked at the number on the belt and fitted the same one, then it would go pop again.
Or they/you both looked up the 'correct' belt using the chassis number, and the pulley has been updated in the dim and distant past, then the 'correct' belt would be the wrong belt.
As an aside - has your belt tensioner thingy still got the plastic outer-wheel on the metal inner-wheel? (Mine hasn't and I replaced the belts a while back and the metal inner-wheel hasn't trashed my new belt)
Example of pulley-update-confusion displayed by our american cousins:
http://rennlist.com/forums/993-forum/497331-update... (ETA whoops)
Are you confused yet?
Or they/you both looked up the 'correct' belt using the chassis number, and the pulley has been updated in the dim and distant past, then the 'correct' belt would be the wrong belt.
As an aside - has your belt tensioner thingy still got the plastic outer-wheel on the metal inner-wheel? (Mine hasn't and I replaced the belts a while back and the metal inner-wheel hasn't trashed my new belt)
Example of pulley-update-confusion displayed by our american cousins:
http://rennlist.com/forums/993-forum/497331-update... (ETA whoops)
Are you confused yet?
Edited by Orangecurry on Monday 21st November 15:46
Confused? Well I was until you changed the linky 
OPC fitted the originals and I'd assume the Indy took the numbers off those. I've had a quick look at the link you posted and without seeing the car can't tell.
Whichever belt was installed I can't understand why the belts would self destruct, slip yes, but litterly break up as they did, especially on the mileage of the second one.
Tension wheel plastic still on, I do remember reading they wear the belt out quicker because of it being there to tell you the belt has snapped
OPC fitted the originals and I'd assume the Indy took the numbers off those. I've had a quick look at the link you posted and without seeing the car can't tell.
Whichever belt was installed I can't understand why the belts would self destruct, slip yes, but litterly break up as they did, especially on the mileage of the second one.
Tension wheel plastic still on, I do remember reading they wear the belt out quicker because of it being there to tell you the belt has snapped
How many miles did the first one last? ETA you said above - 8K - I should concentrate more at school.
If it's too tight, then it will kill itself. If it is too wide for the channel in the pulley, it will kill itself. If it is too narrow for the channel in the pulley, it can catch in the channel, and kill itself.
What width is the failing belt? 9.5 or 10mm?
If it's too tight, then it will kill itself. If it is too wide for the channel in the pulley, it will kill itself. If it is too narrow for the channel in the pulley, it can catch in the channel, and kill itself.
What width is the failing belt? 9.5 or 10mm?
Edited by Orangecurry on Monday 21st November 16:19
My money would still be on incorrect tension in the belt - did the 2nd belt have the shims moved, or did they just chuck on a new belt?
Interesting thread from the americans. I wouldn't necessarily think yours is suffering from either of the below, but she ain't no garage queen
http://rennlist.com/forums/993-forum/621712-repeat...
Interesting thread from the americans. I wouldn't necessarily think yours is suffering from either of the below, but she ain't no garage queen
http://rennlist.com/forums/993-forum/621712-repeat...
Lorenfb said:
A common problem for both the 964 & 993 is the failure of the fan bearing, This bearing
will eventually fail, as it's a sealed bearing which does not receive any lubrication. Once
the bearing fails, one of the two belts will break, i.e. Each belt turns at a different RPM.
Also, if this bearing is approaching its failure point and binding, either of the two belts
can be damaged and/or break. Bearing failure can also damage the alternator shaft,
requiring replacement of the alternator and possibly the fan itself.
Bottom line: The fan bearing replacement should be a normal maintenance item on all 964/933
engines with 100K+ miles, and/or an additional replacement item when the alternator is
replaced.
Less likely as you said they have checked for play in the pulleys?will eventually fail, as it's a sealed bearing which does not receive any lubrication. Once
the bearing fails, one of the two belts will break, i.e. Each belt turns at a different RPM.
Also, if this bearing is approaching its failure point and binding, either of the two belts
can be damaged and/or break. Bearing failure can also damage the alternator shaft,
requiring replacement of the alternator and possibly the fan itself.
Bottom line: The fan bearing replacement should be a normal maintenance item on all 964/933
engines with 100K+ miles, and/or an additional replacement item when the alternator is
replaced.
trophy said:
I would check the bottom pulley that is on the crank, if the bolt that holds the pulley to the crank comes loose the pulley will wobble and cause the belts to break. I have seen this a number of times.
Well I do know it's the same make, part no and belt size as the original installed that lasted 8k mileage. Though it ain't a Porsche branded item as we couldn't get them soon enough ..... saying that that shouldn't matter surely? So I'd assume the oe belt was correct in width. Would 0.5mm really make a difference (if there is actualy one) so suddenly!
Change the belt yourself next time....... no don't.
But I love this. True mechanic.
https://www.youtube.com/watch?v=BQhfcdQf1QA
But I love this. True mechanic.
https://www.youtube.com/watch?v=BQhfcdQf1QA
Wozy68 said:
Well I do know it's the same make, part no and belt size as the original installed that lasted 8k mileage. Though it ain't a Porsche branded item as we couldn't get them soon enough ..... saying that that shouldn't matter surely? So I'd assume the oe belt was correct in width. Would 0.5mm really make a difference (if there is actualy one) so suddenly!
Ah-ha - I made that same mistake. The non-Porsche branded one that I got first was actually a different size from the Porsche branded one, even though it wasn't. It was.Orangecurry said:
Ah-ha - I made that same mistake. The non-Porsche branded one that I got first was actually a different size from the Porsche branded one, even though it wasn't. It was.
I understand the possible issue, but in less than 30 miles and in the same way over the same distance from startup? ..... I'm not so sure this is a belt issue. Saying that, I know about wood, little on anything else Wozy68 said:
Orangecurry said:
...just chop it in for a 996 - they never go wrong.
Wash your mouth out ....... Nothing wrong with an early amber 996 mind
Edit. I'm a little dense at times, the .5mm width difference in belt was a windup wasn't it . ...... you been in the pub all afternoon on a jolly.
Not a wind-up. (hic)
Is your (replacement) a Gates or Dayco?
http://www.ebay.com/itm/Porsche-964-993-Alternator...
It can all go wrong with a 10mm getting slightly stuck in the pulley, whereas the 9.5 doesn't. Also the 10mm doesn't go down into the pulley/groove as far as the 9.5mm, and so it's tighter - yes you can adjust tightness with the shims.
http://www.pistonheads.com/gassing/topic.asp?h=0&a...
So exactly what dimensions were the 'original' (yes it's in the bin and you didn't look) vs the aftermarket Dayco or Gates.
I bought an aftermarket Dayco or Gates (can't remember which) and I couldn't get it to fit, and then bought a Porsche branded IIRC Dayco which has been perfect for my superior varioram and whichever pulley I have.
Is your (replacement) a Gates or Dayco?
http://www.ebay.com/itm/Porsche-964-993-Alternator...
It can all go wrong with a 10mm getting slightly stuck in the pulley, whereas the 9.5 doesn't. Also the 10mm doesn't go down into the pulley/groove as far as the 9.5mm, and so it's tighter - yes you can adjust tightness with the shims.
http://www.pistonheads.com/gassing/topic.asp?h=0&a...
So exactly what dimensions were the 'original' (yes it's in the bin and you didn't look) vs the aftermarket Dayco or Gates.
I bought an aftermarket Dayco or Gates (can't remember which) and I couldn't get it to fit, and then bought a Porsche branded IIRC Dayco which has been perfect for my superior varioram and whichever pulley I have.
Orangecurry said:
Not a wind-up. (hic)
Is your (replacement) a Gates or Dayco?
http://www.ebay.com/itm/Porsche-964-993-Alternator...
It can all go wrong with a 10mm getting slightly stuck in the pulley, whereas the 9.5 doesn't. Also the 10mm doesn't go down into the pulley/groove as far as the 9.5mm, and so it's tighter - yes you can adjust tightness with the shims.
http://www.pistonheads.com/gassing/topic.asp?h=0&a...
So exactly what dimensions were the 'original' (yes it's in the bin and you didn't look) vs the aftermarket Dayco or Gates.
I bought an aftermarket Dayco or Gates (can't remember which) and I couldn't get it to fit, and then bought a Porsche branded IIRC Dayco which has been perfect for my superior varioram and whichever pulley I have.
Race race race. Vario v proper aircooled Is your (replacement) a Gates or Dayco?
http://www.ebay.com/itm/Porsche-964-993-Alternator...
It can all go wrong with a 10mm getting slightly stuck in the pulley, whereas the 9.5 doesn't. Also the 10mm doesn't go down into the pulley/groove as far as the 9.5mm, and so it's tighter - yes you can adjust tightness with the shims.
http://www.pistonheads.com/gassing/topic.asp?h=0&a...
So exactly what dimensions were the 'original' (yes it's in the bin and you didn't look) vs the aftermarket Dayco or Gates.
I bought an aftermarket Dayco or Gates (can't remember which) and I couldn't get it to fit, and then bought a Porsche branded IIRC Dayco which has been perfect for my superior varioram and whichever pulley I have.
Dayco belts as per the OPC ones (though the originals had Porsche written all over them) .
I'll check with my micrometer tomorrow
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