[doru]

Because I could not find any guides/DIY concerning this topic, I decided to make one.
The story goes like this: Car went to the dealership for the PCV Heating Element recall. Picked up the car and the SA told me that the serpentine belt started to move off the tensioner. Thank you for the heads up. Did some research and realized that not only the N54 should have the tensioner & belt replaced at around 100,000 Km (60 K miles) but ALL Nx engines due to a different layout of the accessory belt and being closer to the engine, which if the belt tensioner fails, the accessory belt can be pushed through the main seal and into the engine. If this happens, it's a big headache and BIG repair bill.
I know I did this procedure on my 335is a while ago. Also, through my research I found out that the aluminum bolt has a big chance of getting deformed over time, which in turn will "sag" the tensioner a little and the belt will start first sliding towards the outer edge, then eventually it will slide off and can end inside the engine.
So once home I opened the hood and checked the position of the serpentine belt. The SA was correct. The belt started to slip ever so slightly off the tensioner pulley.

Now I looked inside the engine bay, no Bentley manual, DIY, nothing. I have Bentleys for the e83 X3, the e9x, e39, e46 but nothing for the f25.
All the other models, you can take off the fan to gain space. To do that, there are few bits that have to come off in order to access the fan.
But the F25 has quite a few "things" in the way, and while thinking "after you take this off, you that one off, then this other part and so on, I realized you dismantle half the front end.....
So there must another way. I just took my tools and started to see if I can fit them together with my hand(s) in between the front of the engine and the fan. And yes, I could.

So here it is.
Tools needed:
- ratchet (I also have a long handle ratchet which is very useful to compress the tensioner)
- T60 torx socket
- E14 e-torx socket
- torque wrench
- a marker

Parts needed:
- mechanical belt tensioner p/n 11288620022 - ordered the INA counterpart, which is the original part, minus the expensive BMW logo. In the package is also the aluminum screw (torx e14) included.

- accessory belt p/n 11287628658 - ordered the Contitech which is the identical original part, again minus the expensive BMW logo.

Realoem guided me wrong and I also ordered a deflection pulley (p/n 11288620023) which in my case was NOT needed. It's item #3 in this diagram.


The procedure is quite simple, and there is plenty of room. In a way....
So I placed the long ratchet with the T60 in the star shaped place of the tensioner and turned it clock wise with one hand, and with the other I slipped off the belt.
Now before going further I drew up the schematic how the belt is routed.
Then I took off the belt.
Then with e14 you take off the aluminum bolt that holds the tensioner.
Next step is making 2 marks at a 90° angle. If you don't have an angle torque wrench (I don't), then this can help with the torque-to-yield procedure. The marks were placed inside the hollow of the tensioner where the aluminum bolt sits. I had one mark at 12'o clock and one at 3'o clock.

Then you route the new belt in position minus the tensioner pulley. I did it this way, because I had to fish the belt portion that is in between the A/C pulley and the crank and there isn't much space. Not having the tensioner in place helped. Once the belt is resting everywhere it needs to be routed (minus the tensioner), I installed the tensioner. Torque the aluminum bolt to 25 N/m. Then, I placed a mark with the sharpie on the bolt at the 12'o clock mark. Then I started to turn the bolt for the torque-to-yield procedure. Because there isn't much room to turn the ratchet, placing the mark helped. The 2nd time I was on the money - exactly 90°.
Once this is done, you place the belt over the tensioner pulley, which should be pretty easy now.
Now check very carefully that the belt is placed correctly in the grooves of the A/C pulley, the crank pulley and the alternator pulley. Once satisfied the belt is routed correctly and is seated where it should, turn clockwise the ratchet with the T60 torx in the tensioner to release tension in order to pull the pin. Once the pin is out, slowly let the ratchet loose tension and let it transfer to the tensioner. Now the belt is installed as well.

Do another visual check, go with your hand where your eyes cannot see, under and behind the A/C & crank pulley, make sure the belt is seated correctly. Once satisfied all is good, start up the car and inspect your job. The belt should turn nicely with no sounds.

Hope the pics make sense, and hopefully this might help someone.

[Wgosma]

Thanks for the details. I have 2012 X3 (N52 motor) w/58K miles on the clock and a new serpentine belt sitting on the workbench, I was planning to replace ONLY the belt.

Upon examining my car the belt sits 'off' the tensioner nearly identical to the pic you've posted. So seems it's time for new tensioner w/idler pulley in addition to the new belt.

Question: if the reason the belt is not properly positioned on the tensioner's idler pulley is due to 'sag' (stretch) of the aluminum bolt which secures the tensioner to the head, why could one not simply remove the drive belt and replace the aluminum bolt? Or....is there something internal to this mechanical tensioner that also contributes to the problem? ...or perhaps more likely the bearing in the pulley is simply worn?
Thanks/Bill

[doru]

Originally Posted by Wgosma

Stuff deleted

Question: if the reason the belt is not properly positioned on the tensioner's idler pulley is due to 'sag' (stretch) of the aluminum bolt which secures the tensioner to the head, why could one not simply remove the drive belt and replace the aluminum bolt? Or....is there something internal to this mechanical tensioner that also contributes to the problem? ...or perhaps more likely the bearing in the pulley is simply worn?
Thanks/Bill

I believe we have a stronger belt. It's wider than all the other i6 belts I used on my different other cars, including a 2007 X3 si with the N52 engine - it has a different belt...
All those belts are narrower - I think 2 less grooves. So maybe it puts more strain on the spring? I am not sure, but I talked to my friend (has BMW repair shop - ex BMW master tech) and he told me that those tensioners might look "fine" but once they sag (because of that bolt), they are a no go
Maybe the axle of the roller starts also to bend? I don't know, but for 60 bux I'm not taking chances.
BTW, the belt I pulled actually looked in excellent shape.......

[BIG_KID]

My car is going to get the PCV recall tomorrow. I wonder what they will say is bad.

[Wgosma]

Completed the new tensioner/idler and belt install. Comments:

(my car currently at 58K miles...had the slightest sign of belt 'offset' from the idler)

- This is doable w/o fan removal; it's tight but not terrible; those with large hands will suffer a bit.

- Failure cause: my opinion is that the cause of things like the belt slipping off the idler is due to idler bearing wear and resultant 'play' that develops in the idler. There is IMO no way this heavy duty cast aluminum tensioner 'bends', ditto for the aluminum bolt that secures it to the motor.

- Based on the small amount of 'play' in my old idler I'd say if one does this work at 80-100K mileage intervals you'll be good. This is about same as I've experienced on my other BMW's (E39's).

Thanks/Bill

[deyrag]

Just an FYI for anyone that comes across this.
As doru says in the first post the idler pulley that realoem says is needed is not. FCPEuro is also incorrect as it is included in their kit KIT-11287628658KT.
This is for 28iX N52 with 8/2011 build date VIN ....L713855