[jaap]

I think my balance belt skipped a tooth. I removed the top half of the belt cover and lined up the mark on the camshaft sprocket and the housing (is this TDC). The mark on the top balance shaft sprocket also lines up perfect with the mark on the back but when looking through the hole for the lower balance shaft the marks don't line up. It looks like it is one tooth of. Could this explain why the car has some vibration, although not as bad as last year when the belt broke, and the exhaust note also seems to have changed?



Jaap

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[sasilverbullet]

Yep, that'll do it!

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[rustech]

It's weird how one tooth tends to make more vibration than 180deg off. The bottom pulley also tends to be the first to skip based on my experiences.

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[jaap]

[quote name='rustech' date='Oct 3 2005, 12:11 AM']It's weird how one tooth tends to make more vibration than 180deg off.  The bottom pulley also tends to be the first to skip based on my experiences.

[right][post="10578"]<{POST_SNAPBACK}>[/post][/right][/quote]



It took me a while to figure out why there was this vibration because initially I only looked at the top balance shaft sprocket. Until this happened I was under the impression that a skipped belt would mean it would be relative to the crank since this drives the belt, so both balance shafts would be out of alignment. But apparently, as you already stated, it can also just skip a tooth on of the balance shafts sprocket itself.



Jaap

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[jaap]

The dealer realigned the balance belt which they say looked good which was also my impression from my first inspection. I assume I don not need to have this belt tension checked again because it was already broken in?



Jaap

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[BruceWard]

Did the dealer loosen the tension on the balance belt to align the lower balance shaft? If so they should have reset it to the correct tension. If it is open and the tools are available I would check the tension.



[quote name='jaap' date='Oct 11 2005, 08:52 AM']The dealer realigned the balance belt which they say looked good which was also my impression from my first inspection. I assume I don not need to have this belt tension checked again because it was already broken in?



Jaap

[right][post="11050"]<{POST_SNAPBACK}>[/post][/right][/quote]

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[jaap]

[quote name='BruceWard' date='Oct 11 2005, 05:08 PM']Did the dealer loosen the tension on the balance belt to align the lower balance shaft?  If so they should have reset it to the correct tension.  If it is open and the tools are available I would check the tension.

[right][post="11052"]<{POST_SNAPBACK}>[/post][/right][/quote]



Yes they loosened the belt and reset the tension using the porsche tool. I can hear the familiar slight whine which was also there when they first did the belt job. I only wonder if it has to be retensioned in about 1500 miles as specified for a new belt.



Jaap

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[Greimann]

My guess would be no on a retention, as the old belt has already stretched and worn in.

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[jaap]

Hi,



[quote name='jaap' date='Oct 2 2005, 11:04 PM']I think my balance belt skipped a tooth. I removed the top half of the belt cover and lined up the mark on the camshaft sprocket and the housing (is this TDC). The mark on the top balance shaft sprocket also lines up perfect with the mark on the back but when looking through the hole for the lower balance shaft the marks don't line up. It looks like it is one tooth of. Could this explain why the car has some vibration, although not as bad as last year when the belt broke, and the exhaust note also seems to have changed?



Jaap

[right][post="10575"]<{POST_SNAPBACK}>[/post][/right][/quote]





Although aligning the balance belt has solved the vibration issue I still feel the car (exhaust note) sounds different than before. I have read before about the exhaust note changing when the belt is misaligned. What actually causes this, is it the vibration of the exhaust system you hear. May be the issues were not related at all. Are there things I can check that would explain why it sounds different (especially between 2500 and 4000 rpm)?



Jaap

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[Cloud9...68]

I haven't checked my belt alignment yet, but I think I might have the same problem. It's a weird coincidence, though - my car has had a bad vibration at idle (which went away as I rev'd it up) since I've owned it, so I finally replaced the motor mounts, and found that one of them was broken in half, so, as expected, the idle has smoothed out considerably.



But a few days after completing the mount replacement, the car has developed the opposite problem - a vibration that starts at 1200 rpm, and stays bad (though doesn't really get worse) as the revs increase. It doesn't matter if the car is running in gear, or if I rev it up in neutral, so that would seem to rule out a driveline issue. The engine doesn't really run rough (e.g. no misfire or anything like that), it just sends a vibration through the car.



A couple of obvious questions: Does my problem sound like it could be caused by the timing belt skipping a tooth? And if so, how difficult is it to fix this? Do the belts (and therefore, gulp, the cams) have to come out, or is it simpler than that? If so, does anybody have a DIY on how to do it? Thanks.

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[jaap]

Hi,



In my case it was the balance belt that skipped a tooth on the lower sprocket and not the timing belt. It was an easy fix but requires a special porsche tool for setting the correct tension of the belt, although some set it by feel. No need for the cams to come out unless you are talking about the timing chain between the two cams. I had the dealer correct it because they did the initial belt replacement so was under warranty but could probably have done it myself. I think the tension of the belt is set by a eccentric roller/sprocket which you would also use to loosen the belt and position the balance shafts and then tighten again.

Jaap

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[Dave]

I only wonder if it has to be retensioned in about 1500 miles as specified for a new belt.

Nope, already stretched in. After 1000-2000 miles, they pretty much are done with the stretch.

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