Help diagnose a rattle?

fs34 · 03-05-2021, 02:51 PM

I recently replaced my alternator and after I put it back together I have a rattle. I'm about to take it apart again. I double checked torque on everything and the alternator is now working. No codes.

Bad pulley? I replaced them in December.

Here is the video

I figured I'd ask now before I take it apart again.

DrFerry · 03-05-2021, 03:15 PM

Sounds like the alternator clutch mechanism to me. At WOT the clutch disengages. Perhaps a lose connection whereby the clutch is intermittently engaging and disengaging.

https://www.m3post.com/forums/showth...h#post22438822

fs34 · 03-05-2021, 03:42 PM

Quote:

Originally Posted by DrFerry

Sounds like the alternator clutch mechanism to me. At WOT the clutch disengages. Perhaps a lose connection whereby the clutch is intermittently engaging and disengaging.

https://www.m3post.com/forums/showth...h#post22438822

Alternator is brand new Valeo. Just installed it.

Sound is coming from the PS pump I think, at least that's where I hear it with a stethoscope.

Really confused at this point. Odd coincidence that the PS pump would do this with an alternator replacement. I didn't touch that side of the belts, pulleys etc.

djsilverjohnson · 03-05-2021, 03:56 PM

Sounds like a bearing on its way out. Hopefully just an idler/tensioner.

fs34 · 03-05-2021, 04:13 PM

Better video.

Mimmer · 03-05-2021, 06:17 PM

It almost sounds like something lose or like broke off and bouncing around... if it's new than I doubt it's just the new alt....

Maybe to just rule it out place old one back in and see if it still rattles?

Ajolives · 03-05-2021, 07:12 PM

Quote:

Originally Posted by Mimmer

It almost sounds like something lose or like broke off and bouncing around... if it's new than I doubt it's just the new alt....

Maybe to just rule it out place old one back in and see if it still rattles?

Yeah like a bushing is missing or a mounting bolt and washer isn't tight or too long.

fs34 · 03-05-2021, 10:47 PM

I found the problem, a bolt in the bracket the alternator mounts to backed out.

The last rib of the pulley was worn down by the bolt.

Plan is to use some loctite and reinstall the bolt. I am ordering a new PS pump pulley.

Is the pulley okay to use while I wait for the new one? I have sanded it and it's very smooth.

03-05-2021, 02:51 PM	#1
fs34 Lieutenant 395 Rep 416 Posts Drives: E46 M3 Join Date: May 2019 Location: Huntsville, AL iTrader: (1)	Help diagnose a rattle? I recently replaced my alternator and after I put it back together I have a rattle. I'm about to take it apart again. I double checked torque on everything and the alternator is now working. No codes. Bad pulley? I replaced them in December. Here is the video I figured I'd ask now before I take it apart again.
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03-05-2021, 03:15 PM	#2
DrFerry Field Marshal 6729 Rep 1,829 Posts Drives: '08 E92 M3 Join Date: Jul 2010 Location: Greenville, SC iTrader: (5) Garage List 2008 BMW M3 [5.25] 2015 BMW X5 [4.50]	Sounds like the alternator clutch mechanism to me. At WOT the clutch disengages. Perhaps a lose connection whereby the clutch is intermittently engaging and disengaging. https://www.m3post.com/forums/showth...h#post22438822 __________________ '08 E92 M3 DCT Melbourne Red/Bamboo Beige Leather/EDC/SSP Spec-R DCT clutch discs/SSP Pro-Gold DCT Fluid/Quaife LSD/3:45 Final Drive by Diffs Online/BE Bearings & ARP Bolts/Vibra Technics Engine Mounts/M3 World HFC X-Pipe/LUX H8 180/BPM Sport DCT Tune/PFC Z-Rated Pads/ECS Brass Brake Caliper Bushings/Alex Shop Solid Sub-frame Bushings/Motul 600/Tint
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03-05-2021, 03:56 PM	#4
djsilverjohnson Private First Class 116 Rep 159 Posts Drives: 2013 E93 M3 Join Date: Feb 2020 Location: Georgia iTrader: (0)	Sounds like a bearing on its way out. Hopefully just an idler/tensioner.
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03-05-2021, 04:13 PM	#5
fs34 Lieutenant 395 Rep 416 Posts Drives: E46 M3 Join Date: May 2019 Location: Huntsville, AL iTrader: (1)	Better video.
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03-05-2021, 06:17 PM	#6
Mimmer Lieutenant 57 Rep 412 Posts Drives: E92 13' Join Date: May 2010 Location: WA iTrader: (1) Garage List 2013 e92 m3 [0.00]	It almost sounds like something lose or like broke off and bouncing around... if it's new than I doubt it's just the new alt.... Maybe to just rule it out place old one back in and see if it still rattles?
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03-05-2021, 10:47 PM	#8
fs34 Lieutenant 395 Rep 416 Posts Drives: E46 M3 Join Date: May 2019 Location: Huntsville, AL iTrader: (1)	I found the problem, a bolt in the bracket the alternator mounts to backed out. The last rib of the pulley was worn down by the bolt. Plan is to use some loctite and reinstall the bolt. I am ordering a new PS pump pulley. Is the pulley okay to use while I wait for the new one? I have sanded it and it's very smooth. Attached Images
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