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Old 10-05-2017, 10:27 PM   #1
armenh7
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Bad idler pulley?

Hey guys, I've had this sound forever, but it was never this bad. I first thought it was vanos rattle, but I finally looked up what vanos rattle sounded like and I was completely wrong. I thought vanos rattle was at idle, but I guess not. I searched up bad idler pulley and I'm pretty sure that's it.
Can you guys please confirm? Thank you.
Here's a video:
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Old 10-06-2017, 01:12 AM   #2
LeverThis
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Hi Armenh,

I can't confirm specificly, but to me it sounds both chirpy and growl like a bearing. It could definitely be a pulley on the edge.

Pull off the radiator fan and all the belts and spin every pulley by hand. You should be able to feel and hear the bad ones. Also, spin your water pump, alternator and power steering pump pulleys. Pretty sure an alternator bearing going out can sound like that, but not sure about water & power steering pump. Also, the AC compressor pulley too.

Not sure if the tensioners can go soft, but that might also cause chirping. Something else to keep in mind.
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Old 10-06-2017, 01:36 AM   #3
armenh7
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Originally Posted by LeverThis View Post
Hi Armenh,

I can't confirm specificly, but to me it sounds both chirpy and growl like a bearing. It could definitely be a pulley on the edge.

Pull off the radiator fan and all the belts and spin every pulley by hand. You should be able to feel and hear the bad ones. Also, spin your water pump, alternator and power steering pump pulleys. Pretty sure an alternator bearing going out can sound like that, but not sure about water & power steering pump. Also, the AC compressor pulley too.

Not sure if the tensioners can go soft, but that might also cause chirping. Something else to keep in mind.
Thanks for the response. I can't really take off the belt and do the testing on my own cause I'd have to remove the fan clutch
When I rev up by 100 rpms, the sound goes away.

When I was watching videos on replacing pulleys, I could hear and see what bad ones were like

Last edited by armenh7; 10-06-2017 at 01:37 AM.
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Old 10-06-2017, 02:53 AM   #4
LeverThis
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Quote:
Originally Posted by armenh7 View Post
Thanks for the response. I can't really take off the belt and do the testing on my own cause I'd have to remove the fan clutch
When I rev up by 100 rpms, the sound goes away.

When I was watching videos on replacing pulleys, I could hear and see what bad ones were like
The fan clutch is definitely a pain, although really is hardest the first time if its frozen on there. The 2 piece special tool set for $20 or so on ebay makes it doable. It has a thin 32mm wrench and a counter hold tool that you put on the pulley bolts to hold it still (ifthe belt tension alone isn't enough). This sounds worse than it really is once you get in there.

The fan clutch is reverse threaded so it is impossible for the engine to spin it off and instead wants to tighten it. Thus, on reinstall you can just spin it on hand tight and the next time it will come off easy with only the thin wrench and the belt tension on the water pump pulley. Just dont use the wrench to tighten it down and it'll be easy the next time. Actually, spinning the fan clutch back on and catching the first threads becomes the most annoying part (sometimes very annoying), but it can be worth the access to the entire front end of the engine.
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Old 10-06-2017, 09:07 AM   #5
micky99
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Hi, I believe this is one of your pulleys, most likely the idler close the the alternator. That pulley is the number 1 failure point. A few years ago, I had a beautiful 325ci. Changed the belts and the mechanic said there's no need to change the pulleys. 10 days after, the idler pulley melted shut. This happened on a cold start so it do any damage to the engine and I had a mechanic's shop just around the corner.

What happened was, the new belt was very tight and that didn't go well with the old pulleys. Check if you have a hydraulic/mechanical adjuster as well. I bought a brand new hydraulic at 130k.

When changing the belts, change the whole set!
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Old 10-06-2017, 09:10 AM   #6
armenh7
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Thanks for the replies guys!
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Old 10-06-2017, 09:14 AM   #7
micky99
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No problemo! Be sure to get this done as a priority before the cold weather hits Cali. The sound is probably louder as it's starting to fail badly :-)
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Old 10-06-2017, 09:18 AM   #8
armenh7
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No problemo! Be sure to get this done as a priority before the cold weather hits Cali. The sound is probably louder as it's starting to fail badly :-)
Exactly. It used to be very quiet
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