[MCL968]

As I recall, the pulleys have two key slots, and the cover washer has a tab that goes into the unused slot. When it does that, it exposes one of two symbols stamped into the pulley, one for the top shaft and one for the bottom. If the proper symbol is exposed for the proper balance shaft, then the pulley is installed correctly, assuming the mechanic didn't break off the tab.

 

The most likely cause is the pulley being off a tooth. That happens a lot because new belts are stiff and the shoulders of the belt ribs are not worn in, so the tension on the belts becomes off (looser) as the belts wear in. This allows them to jump a tooth or two. Once they wear in a bit the tension setting is a lot more accurate and they are less inclined to jump.

 

Look at the links on here, they will show you what should be showing through the lower inspection hole and what should be showing on the upper shaft. While the odds of the pulley being on the wrong keyway are low, they are not zero. Most likely it's just that one of the shafts are off a tooth or two.

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[Jamie '92 968]

Thanks Bulti. I guess the key way issue is still in play. Ugh.

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[Jamie '92 968]

And thanks Matt. I didn't see your post last night at first because it had rolled onto a 2nd page and I was reading on my phone. Great summary! The tabs on the cover would seem to be effective in preventing the pulleys from ever being installed wrong. I wonder why someone would break off the tabs!? Yet apparently it happens since the improper installation seems to be relatively common, based on the account in several other posts. Thanks again for all of the advice everybody!

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[Ernie]

Jamie, I don't know who you use as a shop, but Max at Provost in Bordentown, NJ isn't that far from you. I, among others on this forum, give him high marks on his knowledge and skill working on our cars. Just something to consider. I travel a an hour to the shop, and it's well worth the trip!

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[MCL968]

And thanks Matt. I didn't see your post last night at first because it had rolled onto a 2nd page and I was reading on my phone. Great summary! The tabs on the cover would seem to be effective in preventing the pulleys from ever being installed wrong. I wonder why someone would break off the tabs!? Yet apparently it happens since the improper installation seems to be relatively common, based on the account in several other posts. Thanks again for all of the advice everybody!

 

No problem, and one more thing, the lower shaft is the least inclined to jump because of the tension roller and the degree of belt contact with the pulley. The top is probably the culprit, which is good because it's the easiest one to check.

 

Another cause of vibration is shot motor mounts. If everything is lined up, check those next. Mine are on their way out and the cost of GOOD replacements is shocking, especially given the number of cars they fit. It's not like these are one-off motor mounts, but the cost makes it seem like they are.

 

M-

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[Bulti]

It is also perfectly normal that one of either mark is off half a tooth, but never one whole. On my first attempt to replace the belt I had it installed with one tooth off. You have to double and triple-check. Installing it wrong is really easy.


The motor mounts can be measured so you know if they have collapsed or not. Buy ONLY OEM!

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[Jamie '92 968]

Yeah. Just checked Pelican Parts. OEM is $237 each. Two non OEM brand are $36 and $37. Quite a difference. Of course labor costs these days tend to eclipse the parts costs. So you don't want to do it twice.

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[flash]

the problem is the labor.  not a simple job.  the aftermarket ones die after a year or two.  more expensive to do the job wrong twice than right once

 

tip mounts are even pricier.  i just did the ones on the white car

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[Jamie '92 968]

Well......... just got back from the shop, and after a lot of doubts expressed about why the vibration was coming from something other than the balance shafts, including the motor mounts (which by the way are still good after 25 years and almost 200k miles ) they checked the balance belt and..... it was off by a tooth!

Amazing the difference now that it's back in sync. The engine is as smooth as glass !

I knew the vibes were too high, but back to back it is amazing how much difference that 1 tooth makes.

The shop owner apologized and told me that he had "learned not to doubt the guy who has been driving the same car every day for 22 years."


Thanks again for all of the advice and information. In the end it wasn't as complicated or contentious as I feared it might be, but I got a good nights sleep last night with the peace of mind that comes from knowledge and a great support system.

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[ds968]

Always glad to hear these kind of results .

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