Changing the alternator drive belt on a 993
Discussion
Hello there
The alternator drive belt snapped on my way back from work last night. the AA got me home. I was just wondering if its a big job putting a new one on. Do i need any special instruments is it hard or quite straight forward??
Its a pre varioram 1995 993.
Many thanks if anyone has any advice.
Kind regards
Jez
The alternator drive belt snapped on my way back from work last night. the AA got me home. I was just wondering if its a big job putting a new one on. Do i need any special instruments is it hard or quite straight forward??
Its a pre varioram 1995 993.
Many thanks if anyone has any advice.
Kind regards
Jez
It's not very hard but make sure you use Porsche belts and not after-market ones. These can cause misfires believe it or not.
You need a spline tool for the end of the alternator shaft, besides that nothing special. Hardest bit is getting the tension right as it's done with shims. Porsche undated the pulley, might be an idea to change to the new one while you're there
You need a spline tool for the end of the alternator shaft, besides that nothing special. Hardest bit is getting the tension right as it's done with shims. Porsche undated the pulley, might be an idea to change to the new one while you're there
Your right I wouldn't believe it.
Any decent belt for your car will be fine, the Porsche ones are nice as they have Porsche written on them, but I really wouldn't worry if you need to use a halfords or other accessory shop to get the car back on the road quickly.
As above and I am working from memory here you need a torx or spline tool I forget which to hold the alternator shaft, from memory it is spline 12 point, you can use an allen key but be careful. Then undo the allen bolts or nuts depending on which year your car is there are 3 holding the two halves of the pulley together, you will fins some spare shims usually under the bolts, then seperate the halves, fit new belt and trial tighten up, if too loose (you want a bit of wiggle in the belt about 1" max from memory) or too tight add or remove shims as required and place on outside of pulley.
It sounds complex but when you get in there it is just logical and not hard if you take your time, take a cuppa out with you, I think the process is described in the owners manual.
Any decent belt for your car will be fine, the Porsche ones are nice as they have Porsche written on them, but I really wouldn't worry if you need to use a halfords or other accessory shop to get the car back on the road quickly.
As above and I am working from memory here you need a torx or spline tool I forget which to hold the alternator shaft, from memory it is spline 12 point, you can use an allen key but be careful. Then undo the allen bolts or nuts depending on which year your car is there are 3 holding the two halves of the pulley together, you will fins some spare shims usually under the bolts, then seperate the halves, fit new belt and trial tighten up, if too loose (you want a bit of wiggle in the belt about 1" max from memory) or too tight add or remove shims as required and place on outside of pulley.
It sounds complex but when you get in there it is just logical and not hard if you take your time, take a cuppa out with you, I think the process is described in the owners manual.
I welcome any proof to the contrary, but as far as I know Porsche do not manufacture belts, they have them made by a belt manufacturer (Gates?) but with their name on them, much like Textar and Pagid make the brake pads that come in Porsche boxes. Therefore a decent belt without a the 7 magic letters on it will not cause any harm.
I wouldn't have believed the misfire story either but there's a Rennlist thread on it. From memory if the size of the belt isn't exactly right it doesn't ride correctly in the pulley groove and moves up and down in the groove slightly, causing small random changes in the speed of the crankshaft which the ECU sees as a misfire.
In any case make sure the size of the belt is an exact match.
In any case make sure the size of the belt is an exact match.
I agree with the previous post - make sure you quote the size on the belt when you get a replacement. I quoted the chassis number and ended up with the wrong size.
Job is straight forward and there is a page on P-car which takes you through it all: http://p-car.com/diy/vbelt/
Job is straight forward and there is a page on P-car which takes you through it all: http://p-car.com/diy/vbelt/
Here's the thread: http://forums.rennlist.com/rennforums/showthread.p...
Note the last two posts which indicate that it might never cause an issue on OBD 1 cars - that would include UK non-turbo 993s.
Note the last two posts which indicate that it might never cause an issue on OBD 1 cars - that would include UK non-turbo 993s.
phelix said:
I wouldn't have believed the misfire story either but there's a Rennlist thread on it. From memory if the size of the belt isn't exactly right it doesn't ride correctly in the pulley groove and moves up and down in the groove slightly, causing small random changes in the speed of the crankshaft which the ECU sees as a misfire.
In any case make sure the size of the belt is an exact match.
I can see it's a good idea to get the right sized belt and make sure it's fitted properly but the shims allow for slight size differences. Given that the crankshaft is the thing driving the belt I'm confused how anything attached to it could create a force significant enough to speed up or slow down the speed of the engine - the belt would slip on the pulleys before it could exert enough force on a 250+ bhp engine to slow it down, surely?In any case make sure the size of the belt is an exact match.
Me, I always say better safe than sorry. The porker belt is hardly serious money so why take the risk?
As I understand it, the wrong size/od belt slips or causes resonances in the engine close enough to the harmonics in the knock sensor system to fool the knock sensors into thinking the engine is "pinking". Accordingly it retards the ignition. May be rubbish, but as I said above, why risk it?
I'm sure Porsche don't make the belts themselves, but then again they don't make any of the electrics themselves or many of the car's oily bits, but I think most people will accept that there are differences between OE/OE quality parts and cheaper parts from other manufacturers.
I bought some front discs for a Ford Focus from Europarts recently and the OE quality ones were something like 50 quid. I could however have bought ones for 9 pounds. 9 pounds. One might argue they're just chunks of cast iron, no rocket science attached to 'em, but I suspect there's more to it than that. Sometimes you do get what you pay for.
Just my tuppence.
As I understand it, the wrong size/od belt slips or causes resonances in the engine close enough to the harmonics in the knock sensor system to fool the knock sensors into thinking the engine is "pinking". Accordingly it retards the ignition. May be rubbish, but as I said above, why risk it?
I'm sure Porsche don't make the belts themselves, but then again they don't make any of the electrics themselves or many of the car's oily bits, but I think most people will accept that there are differences between OE/OE quality parts and cheaper parts from other manufacturers.
I bought some front discs for a Ford Focus from Europarts recently and the OE quality ones were something like 50 quid. I could however have bought ones for 9 pounds. 9 pounds. One might argue they're just chunks of cast iron, no rocket science attached to 'em, but I suspect there's more to it than that. Sometimes you do get what you pay for.
Just my tuppence.
thegoose said:
phelix said:
I wouldn't have believed the misfire story either but there's a Rennlist thread on it. From memory if the size of the belt isn't exactly right it doesn't ride correctly in the pulley groove and moves up and down in the groove slightly, causing small random changes in the speed of the crankshaft which the ECU sees as a misfire.
In any case make sure the size of the belt is an exact match.
I can see it's a good idea to get the right sized belt and make sure it's fitted properly but the shims allow for slight size differences. Given that the crankshaft is the thing driving the belt I'm confused how anything attached to it could create a force significant enough to speed up or slow down the speed of the engine - the belt would slip on the pulleys before it could exert enough force on a 250+ bhp engine to slow it down, surely?In any case make sure the size of the belt is an exact match.
At 10-15 quid the key is worth buying, although doesn't the tool kit have an allen key in to do the job? My 964 had all the tools to do alternator belts.
The other job you really do need spline keys for are the door catches attached to body on 964 and I assume 993, if you try to use allen keys then unless your seriously lucky you will just strip the head.
The other job you really do need spline keys for are the door catches attached to body on 964 and I assume 993, if you try to use allen keys then unless your seriously lucky you will just strip the head.
Guys thank you all very much for all the top tips. A real wealth of knowledge!!
I thought long and hard and took it to GT one in the end, who have fixed the new belts. There was a problem as most of it had corroded which made the job take longer so was pleased i did.
Thanks again for all your helpful tips.
Many thanks
Jez
I thought long and hard and took it to GT one in the end, who have fixed the new belts. There was a problem as most of it had corroded which made the job take longer so was pleased i did.
Thanks again for all your helpful tips.
Many thanks
Jez
Gassing Station | Porsche General | Top of Page | What's New | My Stuff