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My 1991 560SEL has a rattling sound in the engine bay, its coming from the passenger side. I have replaced the Timing Chain Tensioner, but the sound is still here. What else could it be, a bad clutch from the alternator...? I will post a video later, once I get home. Thanks
 

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I would guess the air pump bearing. It gets dirty and jams up completely which then gives you belt screeches. I have not seen the brearing replacement for sale in car parts sites, because you need proper vice and some tapping to remove the bearing. Machine shops can do it. The bearing is one of these:
Assorted bearings. You need to get the one that fits.
Easy test would be to remove the belt to the Smog air Pump and see if it goes away.
Reconditioned Air Pumps, of course is the normal fix. Those go for around $200.
 

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I used the old screwdriver trick, it's the alternator bearing. I disconnected the belt to see if it would stop, and it did. Do I put in a new (rebuilt) alternator, or can I change the bearing? Thanks
 

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If it's only the bearing, the air pump part is probably fine. Getting the right bearing is some work. I have the same problem. I redid the air pump for $180 and the bearing went out again in 2 years. I'd rather change the bearing for $20 plus another $20 to a machine shop. Trouble is finding the exact right bearing that fits. Pulling it out will give you the one that you can measure. And the car will run fine without the air pump. There might be some issue with leaving it off, but I have not heard that, except you could fail smog. I have the same issue to fix, so let me know how it goes.
 

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I used the old screwdriver trick, it's the alternator bearing. I disconnected the belt to see if it would stop, and it did. Do I put in a new (rebuilt) alternator, or can I change the bearing? Thanks
I think you'd be ahead by simply replacing the alternator. If you're set up for pulling and pressing bearings I'd be tempted but you have to consider the time to research the proper size and type bearing, labor to install, etc.
 

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Except for the Geico add in the middle, this is how the forum is supposed to work from #1 to #9. Thanks to Swiss Cheese for not forgetting to provide results of question/research and commentators for advice.

My Swiss Cheese story. All can stop here if you want to. In Geneva, I noticed a US tourist lady looking dubiously at the enormous selection of cheeses displayed at my local supermarket (about an aisle long) and she asked the attendant "but where is the swiss cheese?" With a sweep of his arm, he answered "Madame, voila, this is all swiss cheese." :)
 
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