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BMW 3-Series (E90 E92) Forum > E90 / E92 / E93 3-series Technical Forums > DIY Guides > DIY-Replacing N52 tensioner, idler pulley and serpentine belt



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TwinT1addict's Avatar DIY-Replacing N52 tensioner, idler pulley and serpentine belt
TwinT1addict
12-24-2011
Welcome everyone. As you may know i have up in the general section about changing my belt tensioner, belt and idler pulley. I completed this job successfully and will do the best i can to write my first DIY to replace the tensioner, serpentine belt and idler pulley...
  #44  
By Spy021 on 10-07-2012, 05:43 PM
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Quote:
Originally Posted by AlanAZ View Post
It would cause increased belt wear and pre-mature belt failure -- that could leave you stranded somewhere, and could, outside chance, damage the A/C compressor.

Check that the belt is running in a flat plane between all the pulleys, and the tensioner is not forward or back. Look for wear on the edge of the belt. A couple of people have reported broken mounting bolt on the tensioner, look for that. See the above thread for details and photos.
I had the same issue with a crooked tensioner and decided it was best to play it safe and change it out for all the reason quoted. It's a pretty simple job, even coming from someone with limited skills like myself. The last thing you want is that belt coming off while you are driving.
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  #45  
By teammurbs on 10-20-2012, 09:53 AM
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cheap place i ordered online

i bought both the tensioner and idler pulley including shipping for only $93 after shopping online for a bit. www.oembimmerparts.com
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  #46  
By kiwi29 on 11-25-2012, 01:32 AM
I'm gonna be replacing my belt sometime this week. Any pointers/tips for a 1st timer?
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  #47  
By mocny77 on 01-10-2013, 11:46 AM
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Thanks
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  #48  
By Dalco450 on 01-18-2013, 12:57 PM
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Just did it!

Thank you for your DIY. It took me only 20 minutes to replace the tensioner, the idler pulley and the serpentine belt. I took a 16 inches ratchet with a T60 to unload the tensioner in front of the car and it wasn't hard at all with that. I know, I'm very strong for my 160lbs... The idler pulley have a 16mm bolt and the tensioner's bolt took me a E14 torx box.
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  #49  
By TwinT1addict on 01-27-2013, 12:18 AM
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Quote:
Originally Posted by Dalco450 View Post
Thank you for your DIY. It took me only 20 minutes to replace the tensioner, the idler pulley and the serpentine belt. I took a 16 inches ratchet with a T60 to unload the tensioner in front of the car and it wasn't hard at all with that. I know, I'm very strong for my 160lbs... The idler pulley have a 16mm bolt and the tensioner's bolt took me a E14 torx box.
Good to hear you got it done. Glad i could be of help.
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  #50  
By index1489 on 02-28-2013, 12:58 PM
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Straight from TIS, those numbers mean a specific section of the Torque Specification Document.

This is ONLY for N52 engine, the 335i N54/N55 might be different.

Torque to 18 ft pounds for the tensioner, THEN torque it 90 degrees ignoring the torque. This is known as Torque to Yield or Torque to Angle, and I believe streches the bolt and allows for more consistency then if they just gave you a flat torque number.

No where in TIS did I find the specs for the idler pulley, but the idler pulley on the alernator is 40nm or about 30ft lbs so I'm going with that.



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  #51  
By Spy021 on 04-09-2013, 08:52 PM
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So I replaced the idler pulley, tensioner, and belt about a year ago (03/11/12) using this DIY as the belt was riding about a 1/4 inch off of the tensioner. After replacing everything I checked the belt a few times a week for the first month to ensure that everything was still seated properly and looked good. Fast forward to tonight and while looking under the hood to see if I could figure out where a squeaking was coming from, I noticed that the belt had once again begun to ride off the tensioner about a 1/4 inch.

Has anyone else seen this happen again after changing out the idler pulley, tensioner, and belt? It's a relatively simple job if I have to do it again, but I'm a little aggravated that this would happen again in such a short period of time and especially considering I have to buy all of the parts again!
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  #52  
By ska///235i on 04-21-2013, 09:02 PM
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all parts are available from autohausaz for $112

so whats everyone's mileage when they change the belt and pulleys???
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  #53  
By Spy021 on 04-22-2013, 11:29 PM
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I replaced my idler pulley, tensioner, and belt on my 07 at 64,227 miles.
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  #54  
By Pr0metheus on 05-25-2013, 10:50 AM
2006 330i Sedan (07/2005)
106,xxx Miles -- no record of them being changed before....

I am gathering pricing info now to do this, thanks for the Autohausaz tip!
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  #55  
By JS82 on 06-14-2013, 01:24 AM
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Quote:
Originally Posted by index1489 View Post
Straight from TIS, those numbers mean a specific section of the Torque Specification Document.

This is ONLY for N52 engine, the 335i N54/N55 might be different.

Torque to 18 ft pounds for the tensioner, THEN torque it 90 degrees ignoring the torque. This is known as Torque to Yield or Torque to Angle, and I believe streches the bolt and allows for more consistency then if they just gave you a flat torque number.

No where in TIS did I find the specs for the idler pulley, but the idler pulley on the alernator is 40nm or about 30ft lbs so I'm going with that.

I have found the following on TIS and on the Bentley Repair Manual (sorry for the crappy iphone pics).
It looks like the idler pulley on the alternator has to be installed with 80Nm or 59 ft-lbs.





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  #56  
By ska///235i on 06-14-2013, 10:43 AM
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Oh, then i'll need to retorque mine

Makes sense cuz that bolt is pretty big
Last edited by ska///235i; 06-14-2013 at 10:31 PM.
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  #57  
By LittleBlue on 06-18-2013, 08:27 AM
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Hi all, I recently developed a whistling or howling notice at certain speeds, at first thought I was thinking the rear differential , then maybe a bearing , it is hard to determine where the sound is coming from, but now I think it's from the engine. As I started the car first thing this moring I was hearing the sound slightly, like metal on metal ( bad bearings ) sonds, but when driving it gets louder based on engine speed, could I be looking at same issue, I know I can test by removing the belt but wondering if you experienced the sound while driving as well.

Thanks,
__________________
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  #58  
By McAuley7 on 06-18-2013, 09:10 AM
I see everyone is buying oem parts but advance auto, a tensioner pully is $30 and Napa $16, Bad idea?
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  #59  
By LittleBlue on 06-19-2013, 07:40 AM
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Quote:
Originally Posted by Sonic777
I see everyone is buying oem parts but advance auto, a tensioner pully is $30 and Napa $16, Bad idea?
I would stick with OEM if you're keeping the car.
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  #60  
By LittleBlue on 06-19-2013, 07:45 AM
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Do these parts have to be OEM ?
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  #61  
By reppin513 on 06-21-2013, 05:19 PM
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I was planning on just replacing the belt because it started squealing this morning and when I checked it after work the belt was a 3/4" off the tensioning pulley at an angle, worn on the side it was rubbing. I took the belt off just now and think at least the tensioning pulley spins freely and barely makes that grainy sound. I saw videos saying that means the bearings are bad. Im still inclined to keep the pulley because it is spinning well, after all, and my relative very versed in this sort of repair, though not on BMWs, said not to replace stand alone pulleys (those not powering anything) if they spin well. He recommended only replacing them if they are becoming seized or cause extra friction to the belt, etc. Do you have any thoughts on this? Im going to just put the new belt on and wait for a solid reply/something to break. Thanks.
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  #62  
By AlanAZ on 06-22-2013, 08:48 AM
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Quote:
Originally Posted by reppin513 View Post
I took the belt off just now and think at least the tensioning pulley spins freely and barely makes that grainy sound. I saw videos saying that means the bearings are bad. Im still inclined to keep the pulley because it is spinning well, after all, and my relative very versed in this sort of repair, though not on BMWs, said not to replace stand alone pulleys (those not powering anything) if they spin well. He recommended only replacing them if they are becoming seized or cause extra friction to the belt, etc. Do you have any thoughts on this? Im going to just put the new belt on and wait for a solid reply/something to break. Thanks.
If you spin a new pulley, they do not free freely, and make no grainy sound. The fact yours do, means the lubrication is gone, and the next step is the bearings will go bad. It worth the risk to be stranded and possible damage to your accessories if the belt breaks?
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  #63  
By reppin513 on 06-22-2013, 03:45 PM
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Quote:
Originally Posted by AlanAZ View Post
If you spin a new pulley, they do not free freely, and make no grainy sound. The fact yours do, means the lubrication is gone, and the next step is the bearings will go bad. It worth the risk to be stranded and possible damage to your accessories if the belt breaks?
I actually replaced the tensioner bc it ended up having a badly rounded bolt that wouldn't hold tension. Im going to wait to do the other pulley that is recommended when I have family back from vacation and don't need to have reliable transportation by tonight. I am about to unspring the tensioner now by pulling the pin, but it seems like there is too much slack even with the belt run correctly. Am I supposed to use a male t60 on the right of the tensioner before pulling the pin? Thanks for your help.
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  #64  
By reppin513 on 06-22-2013, 04:34 PM
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Quote:
Originally Posted by reppin513 View Post
I actually replaced the tensioner bc it ended up having a badly rounded bolt that wouldn't hold tension. Im going to wait to do the other pulley that is recommended when I have family back from vacation and don't need to have reliable transportation by tonight. I am about to unspring the tensioner now by pulling the pin, but it seems like there is too much slack even with the belt run correctly. Am I supposed to use a male t60 on the right of the tensioner before pulling the pin? Thanks for your help.
Ok so I got some slack out, stripping both the male and female t-60 bolts/slots on the new tensioner. How do you pull the pin when you cant take some load off the spring? its too tight to get any real pull on it from a vertical angle. How have you solved this dilemma?
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  #65  
By AlanAZ on 06-22-2013, 10:18 PM
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Quote:
Originally Posted by reppin513 View Post
Ok so I got some slack out, stripping both the male and female t-60 bolts/slots on the new tensioner. How do you pull the pin when you cant take some load off the spring? its too tight to get any real pull on it from a vertical angle. How have you solved this dilemma?
It does take some leverage to un-tension the tensioner. I used a breaker bar. If your racket handle is shorter, perhaps you can lengthen by putting a piece of pipe over it, or cable tie a rod to it..
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