N54 Serpentine Belt Tensioner

Blackhawk36 · 08-08-2012, 06:35 PM

I took the belt off and there is no knock at all. So it is something to do with a belt driven accessory. All of the pulleys moved freely with no roughness or looseness. I did check the alternator pulley. Problem is I don't know what it should do. Based on what moparaker is saying the pulley is a sprag (overrunning) clutch. I put a 12 point socket in the alternator shaft to hold it steady and a strap wrench around the pulley and tried to turn the pulley. I can't turn it in either direction. I can get the pulley from the dealer. I sure hope that is the problem.

badass335 · 08-08-2012, 08:04 PM

Its a bit of a battle. I know all about it. Had a knock at first. Then a ticking sound but only when car had load. Not the lifters or hpfp or the vanos. Took her in and basically went through a slew of things.
1-Alternator. Replaced. Noise different but still there.
2-bottom idler pulley. replaced. noise still there but pulley was cracked?
3-A/C compressor. Replaced, noise still there so dealer put old one back in. (No charge!)
4-Middle tensionors. Replaced noise still there
5-power steering pump. Noise gone finally.

In short, pretty much every damn thing on that side! I also had my entire engine replaced before due to the subframe issue previous year so not sure if these pulleys were used from the old engine. (Pulleys hit subframe and parts of my shredded belt were found in the engine head.)

Blackhawk36 · 10-12-2012, 03:50 PM

Problem is fixed. It was the alternator pulley. It is the Overrunning Alternator Decoupler (OAD) type. It has a sprag clutch and shock absorbing spring in the pulley assemble. Mine was locked up in both directions. That evidently caused the tensioner to deflect too far on startup causing a knock. All is fixed now.

Anthrax-VX · 09-23-2021, 02:38 AM

Quote:

Originally Posted by Blackhawk36

Problem is fixed. It was the alternator pulley. It is the Overrunning Alternator Decoupler (OAD) type. It has a sprag clutch and shock absorbing spring in the pulley assemble. Mine was locked up in both directions. That evidently caused the tensioner to deflect too far on startup causing a knock. All is fixed now.

Did you replace the clutch mechanism or dislodge it somehow? (nm i just saw that its an easy part to purchase and replace, ordered from FCP euro) i was definitely under the impression that it was the pulley as well, since u can see it slap on startup, but ill go ahead and change this (this car was purchased as a favor to a friend, he said it just needed turbos, so i did that, while under there, found a host of issues, im now 7k in parts into this thing lol)

mapleleaf1773 · 09-23-2021, 05:10 AM

Dude, he isn't going to respond. It was 9 years ago.

08-08-2012, 06:35 PM	#23
Blackhawk36 Captain 30 Rep 644 Posts Drives: 2007 335i 6MT No iDrive Join Date: May 2009 Location: MD iTrader: (0)	I took the belt off and there is no knock at all. So it is something to do with a belt driven accessory. All of the pulleys moved freely with no roughness or looseness. I did check the alternator pulley. Problem is I don't know what it should do. Based on what moparaker is saying the pulley is a sprag (overrunning) clutch. I put a 12 point socket in the alternator shaft to hold it steady and a strap wrench around the pulley and tried to turn the pulley. I can't turn it in either direction. I can get the pulley from the dealer. I sure hope that is the problem.
	Appreciate 0 Quote

08-08-2012, 08:04 PM	#24
badass335 Lieutenant Colonel 109 Rep 1,948 Posts Drives: 2017 540i Xdrive Join Date: Jul 2007 Location: Surrey, BC iTrader: (10)	Its a bit of a battle. I know all about it. Had a knock at first. Then a ticking sound but only when car had load. Not the lifters or hpfp or the vanos. Took her in and basically went through a slew of things. 1-Alternator. Replaced. Noise different but still there. 2-bottom idler pulley. replaced. noise still there but pulley was cracked? 3-A/C compressor. Replaced, noise still there so dealer put old one back in. (No charge!) 4-Middle tensionors. Replaced noise still there 5-power steering pump. Noise gone finally. In short, pretty much every damn thing on that side! I also had my entire engine replaced before due to the subframe issue previous year so not sure if these pulleys were used from the old engine. (Pulleys hit subframe and parts of my shredded belt were found in the engine head.)
	Appreciate 0 Quote

10-12-2012, 03:50 PM	#25
Blackhawk36 Captain 30 Rep 644 Posts Drives: 2007 335i 6MT No iDrive Join Date: May 2009 Location: MD iTrader: (0)	Fixed. Problem is fixed. It was the alternator pulley. It is the Overrunning Alternator Decoupler (OAD) type. It has a sprag clutch and shock absorbing spring in the pulley assemble. Mine was locked up in both directions. That evidently caused the tensioner to deflect too far on startup causing a knock. All is fixed now.
	Appreciate 0 Quote

09-23-2021, 05:10 AM	#27
mapleleaf1773 First Lieutenant 418 Rep 411 Posts Drives: 2011 BMW 328i XDrive Join Date: Jan 2021 Location: West Virginia iTrader: (0) Garage List 2011 BMW 328i XDrive [0.00]	Dude, he isn't going to respond. It was 9 years ago.
	Appreciate 0 Quote