- 11287628653 - serpentine belt
- 11287582946 - mechanical belt tensioner (mine came with new protection cap)
- 11287578674 - deflection pulley (mine came with new protection cap)
- 11287795159 - protection cap for above if required
- 11287578675 - deflection pulley (mine came with new protection cap)
- 11287544616 - protection cap for above if required
- T20 Torx bit
- T60 Torx bit
- T50 Torx bit
- Torque wrench
- 10mm socket and small ratchet
- Small flat bladed screwdriver or pry bar
- Optional tiny screwdriver
- Telescopic magnet
- Decent pliers
2. Disconnect the fan power supply and unhook the clips holding the wire in place across the top of the radiator. Place the wire off to the left side of the engine bay out of the way (you'll thank me later).
3. Remove the hose from the two clips on the radiator and hook it out the way behind the aircon line conveniently placed for just this purpose.
4. Now the unnecessarily awkward bit. Looking at the next few images, you'll see the clips on both sides of the fan shroud, plus a 10mm bolt. Remove the bolt then manipulate the shroud out of the clips. I managed to unhook mine from the left-hand clip by lifting slightly (it's only resting in it), then I moved the whole shroud to the left a little which let the right-hand clip come free. After the shroud is free of both clips, it can be lifted straight upwards by moving any hoses out of the way as it comes out.
5. This next photo shows the original tensioners and belt in place with the belt path highlighted. Using the torque wrench and the T60 Torx bit, turn the whole 11287582946 tensioner housing clockwise to de-tension the belt. Optionally, if doing this solo, I found it easier to use a tiny flat blade screwdriver to lock the tensioner in its de-tensioned state as it's spring-loaded and will just return to tensioned again. If you have your replacement part to hand, you can see a bar pre-fitted in the same manner to aid fitment later on. Now you can go ahead and remove the belt from the various pulleys. Then, using the larger flat blade or a small pry bar, pop the caps off the pulleys to reveal the T50 Torx bolts that need to be removed. Undo these anti-clockwise.
6. Next image shows all tensioners removed. I was very chuffed to see there was no oil leaks on this engine; bone dry
7. Replace all tensioners and torque to specs as shown below (specs from NewTis).
8. Install the belt, careful to ensure it follows the original path. Note the lockout bar still in place. DO NOT remove this until you have the belt run and you're sure it's seated correctly on all the ribbed pulleys and tensioners correctly.
9. When happy that the belt's seated correctly, use the T60 and torque wrench (clockwise) to de-tension the pully and remove the lockout bar with a pair of pliers. Gently release the clockwise pressure and the belt should go tight. Install the new caps.
10. If you followed my advice earlier, you moved the fan power supply all the way to the left side of the engine bay by popping all the clips out. You can now plug in the fan when the shroud is propped up by the front wheel and start the car to test the new belt and pulleys without any error messages appearing. Once tested, re-install the fan assembly, hose, fan motor wiring and the cold air intake. Done.
Hope this helps someone. There are a few videos on YouTube (although I couldn't find one specific to the N55 135i) but all the ones I found didn't give the torque specs and didn't cover how to remove the fan and shroud assembly.
Note that upon removal one of my pulleys was spinning freely (the new ones have a bit of resistance) and was making a slight bearing noise, so definitely needed replacement. The other originals were all quiet and had a little bit of resistance like the new replacements.