cam sprocket replace?
#1
Burning Brakes
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I seem to remember reading somewhere that if the surface of the tops of the teeth on the cam sprocket are worn and shiny then they need to be replaced. Mine are shiny and have a bit of an uneven wear pattern to them. If you hold a straight edge across the surface there is a slight concave wear spot...shiny except at the two edges of the tooth. You could slip a piece of notebook paper between the straight edge and the top of the tooth, maybe even a business card thickness piece of paper.
The belt seems to ride just front of center also but I've read Porken found that to be a good thing, in that, he found most failures had the belt riding more toward the back of the sprocket.
Here's a pic, sorry the little camera didn't focus on the tooth surface, I'll probably replace this pic later tonight when I get back up to the garage. But then again maybe you can tell enough from this one and my description to say whether or not it's time for new sprockets. If it's time to replace is there any other while your in there stuff I should consider. This while you're in there stuff is killing me! I did order Porkens tool already so I guess I'll be making good use of it now...
The belt seems to ride just front of center also but I've read Porken found that to be a good thing, in that, he found most failures had the belt riding more toward the back of the sprocket.
Here's a pic, sorry the little camera didn't focus on the tooth surface, I'll probably replace this pic later tonight when I get back up to the garage. But then again maybe you can tell enough from this one and my description to say whether or not it's time for new sprockets. If it's time to replace is there any other while your in there stuff I should consider. This while you're in there stuff is killing me! I did order Porkens tool already so I guess I'll be making good use of it now...
![](http://home.sc.rr.com/willrobinson/928%20refresh/worn%20teeth.jpg)
#2
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The gears are worn and you should consider replacing them, also if you do you should reseal the oil pump O ring and front crank radial seal and both of the cam shaft radial seals as well as the oil pump radial seal along with replacing the oil pump drive pulley and the crank timing belt drive pulley So 4 pulleys 4 radial seals and 1 O ring. Make sure you dont lose the position of the cam pulley to the mount , otherwise you will have to realign the cam to pulley reference, if when your done this job you find that you have lost some power then either a tooth is off on the timing or the cam to pulley reference has been lost. Does the belt have little hairs sticking out of it? if so it indicative of the gears starting to chew the belt teeth. Ahh dont forget to rebuild the tensioner, i use STP oil in it, it seems to not be as prone to leaking with the thinner oils.
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Exactly what MrMerlin said +1
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Does it have the "Do It Yourself" manual transmission, or the superior "Fully Equipped by Porsche" Automatic Transmission?
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Does it have the "Do It Yourself" manual transmission, or the superior "Fully Equipped by Porsche" Automatic Transmission?
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#4
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From my earlier post.... before and after measuring tool....
http://img167.imageshack.us/img167/1...rementsax8.jpg
http://img167.imageshack.us/img167/1...rementsax8.jpg
![](http://img167.imageshack.us/img167/192/camsprocketmeasurementsax8.jpg)
#5
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Mine are shiny and have a bit of an uneven wear pattern to them. If you hold a straight edge across the surface there is a slight concave wear spot...shiny except at the two edges of the tooth. You could slip a piece of notebook paper between the straight edge and the top of the tooth, maybe even a business card thickness piece of paper.
The belt seems to ride just front of center also but I've read Porken found that to be a good thing, in that, he found most failures had the belt riding more toward the back of the sprocket.
The belt seems to ride just front of center also but I've read Porken found that to be a good thing, in that, he found most failures had the belt riding more toward the back of the sprocket.
I haven't 'found' that failures occur from belts riding toward the back, but I have noticed that when the belt is overtensioned, the tensioner pulley gets pushed toward the engine more and more as the bushings wear. Also, used gears with some miles on them will tend to pull a new belt to the last position the old belt was running.
When you put the PKsn'r on with new gears, the position will likely be ~2mm back from the edge.
If you can wait, don't loosen the old cam gears until you recieve your 32V'r, and take a pic of how they were set before. This isn't critical, but it will tell you if the cams had been messed with before, on purpose, or by accident.
When you put new gears on, set the ¼ side to -2°, and the ⅝ side to 0°.
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+1
Since the cam gears are "shiny", I would not think twice about replacing them. You should also check the oil pump gear and the crankshaft gear as well - BTDT. If in doubt, please replace all of them - I would, as sharp edges on any one of the gears would quickly wear out a new timing belt.
Since the cam gears are "shiny", I would not think twice about replacing them. You should also check the oil pump gear and the crankshaft gear as well - BTDT. If in doubt, please replace all of them - I would, as sharp edges on any one of the gears would quickly wear out a new timing belt.
#7
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That gear is toast. Check the rest of the gears, and especially the crank gear to see if it's worn concave, also.
I haven't 'found' that failures occur from belts riding toward the back, but I have noticed that when the belt is overtensioned, the tensioner pulley gets pushed toward the engine more and more as the bushings wear. Also, used gears with some miles on them will tend to pull a new belt to the last position the old belt was running.
When you put the PKsn'r on with new gears, the position will likely be ~2mm back from the edge.
If you can wait, don't loosen the old cam gears until you recieve your 32V'r, and take a pic of how they were set before. This isn't critical, but it will tell you if the cams had been messed with before, on purpose, or by accident.
When you put new gears on, set the ¼ side to -2°, and the ⅝ side to 0°.
I haven't 'found' that failures occur from belts riding toward the back, but I have noticed that when the belt is overtensioned, the tensioner pulley gets pushed toward the engine more and more as the bushings wear. Also, used gears with some miles on them will tend to pull a new belt to the last position the old belt was running.
When you put the PKsn'r on with new gears, the position will likely be ~2mm back from the edge.
If you can wait, don't loosen the old cam gears until you recieve your 32V'r, and take a pic of how they were set before. This isn't critical, but it will tell you if the cams had been messed with before, on purpose, or by accident.
When you put new gears on, set the ¼ side to -2°, and the ⅝ side to 0°.
I'm new to all this so it will probably take me some time to figure out what this means : "When you put new gears on, set the ¼ side to -2°, and the ⅝ side to 0°"
Or does that become more obvious to the uninitiated when the instructions for the tool are studied?
Thanks for all the help by the way!
And on a related note Ken, can you tell me what parts the PKsnr eliminates from the usual order of timing belt/water pump parts? I need to tell Roger what I need. Thanks again everyone!
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#8
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When you have the 32V'r in hand, it's makes more sense. ¼=1-4 cylinders=US passenger side. -2°=2 degrees crank retard.
It's easier to tell you what you need... a tensioner gasket, and a belt!![Big Grin](https://rennlist.com/forums/images/smilies/biggrin.gif)
Maybe a water pump. But, if it doesn't leak, the pump pulley has no play up or down/in or out, nor feels notchy when turned (worn bearings), and doesn't spin too easily (no grease), then many people leave a working water pump in, if they are doing the work themselves. If at some point it leaks, then you can replace it yourself.
If you want, you can put new bearings in the idler(s), under the crank gear, and keep those, but they aren't needed, anymore. You would only miss them if for some reason you want to take the belt off the cam gears, without taking off the balancer, to hold the belt in place on the crank gear. But you can work around that too. I took them off, on all three of my cars.
It's easier to tell you what you need... a tensioner gasket, and a belt!
![Big Grin](https://rennlist.com/forums/images/smilies/biggrin.gif)
Maybe a water pump. But, if it doesn't leak, the pump pulley has no play up or down/in or out, nor feels notchy when turned (worn bearings), and doesn't spin too easily (no grease), then many people leave a working water pump in, if they are doing the work themselves. If at some point it leaks, then you can replace it yourself.
If you want, you can put new bearings in the idler(s), under the crank gear, and keep those, but they aren't needed, anymore. You would only miss them if for some reason you want to take the belt off the cam gears, without taking off the balancer, to hold the belt in place on the crank gear. But you can work around that too. I took them off, on all three of my cars.
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I guess based on what ya'll are saying here this is also bad?? When checking with a stright edge I can see light thru the gap as well as slide 1 sheet of paper thru it.
![](http://i267.photobucket.com/albums/ii310/lutz928/cam/DSC02042Large.jpg)
![](http://i267.photobucket.com/albums/ii310/lutz928/cam/DSC02044Large.jpg)
I will check my oil pump gear, I think it is the same way.
![](http://i267.photobucket.com/albums/ii310/lutz928/cam/DSC02042Large.jpg)
![](http://i267.photobucket.com/albums/ii310/lutz928/cam/DSC02044Large.jpg)
I will check my oil pump gear, I think it is the same way.
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Could you give me your opinion of the oil pump gear. I know is hard from just a pic. but here it is. I don't think the gap is as deep as on the cam gear.
![](http://i267.photobucket.com/albums/ii310/lutz928/cam/DSC02046Large.jpg)
![](http://i267.photobucket.com/albums/ii310/lutz928/cam/DSC02047Large.jpg)
Thanks
![](http://i267.photobucket.com/albums/ii310/lutz928/cam/DSC02046Large.jpg)
![](http://i267.photobucket.com/albums/ii310/lutz928/cam/DSC02047Large.jpg)
Thanks
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My cam and oil gears did not look quite that bad, but I replaced all 4 gears. It is something I will probably never have to do on this motor again with proper tensioning, oil in the tensioner (and maybe a porkensioner).
It is a bit of $$$ up front, but worth the piece of mind if you plan on keeping the car long term. Besides, in 5 years or so, the next TB change will be a whole lot cheaper on parts.
Jim
It is a bit of $$$ up front, but worth the piece of mind if you plan on keeping the car long term. Besides, in 5 years or so, the next TB change will be a whole lot cheaper on parts.
Jim
#13
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The deal on replacing the pulleys is if the cams are both bad then its a safe bet that the drive(crank) pulley is also worn it may not obvious but with a straight edge you should see some sort of wear in the center of the teeth, and usually if the cams are bad you also replace the worn oil pump pulley, usually it is the older style and made of alloy instead of the new version thats made from steel, and it goes with saying to replace as many oil seals as you remove pulleys
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Dave the upside is once your finished your car is good for another 20 years