F10 535i DIY - Auxiliary Belt, Tensioner and Idler Pulley removal and refitting (FEAD)

[Andrew]

The auxiliary drive belt is a consumable part and mine had started to show signs of fraying on its edges at roughly 56,000 miles and 8 years old.  The belt is just one component in the system know as the Front End Auxiliary Drive (FEAD), the other components should be replaced at the same time as they all wear at the same time.  On the N55 without dynamic drive this includes the tensioner and an idler pulley.  There is no Over Running Coupling on the alternator on my N55 so no need to do anything with the alternator drive pulley.

To get to the FEAD, you first need to remove the upper cross brace and then the engine cooling fan so you have sufficient room to get your arms and tools into the gap between the front of the engine and the radiator.

See these posts on how to remove the upper cross brace and fan.

Tools needed – just for this job

Torx T50 bit
Torx T60 bit
E12 Socket
10mm socket
4.5mm dia drill bit
Flat small screwdriver
Ratchet
Breaker bar
Torque wrench 38Nm – 60Nm

 

Parts needed

Drive belt 8PK1390  - 11287628661
Tensioner - 11288604266
Idler pulley - 11288673720

 

The edges of my auxiliary belt are just starting to wear at just over 8 years old and 56.167 miles on the clock.  If the belt is starting to wear, chances are so to are the rest of the components, the tensioner and the idler pulley.

These are the new aftermarket parts I chose to fit along with a new bolt (from BMW) that fixes the tensioner to the block

Once you have removed the upper cross brace and the fan, this is the view you are met with.

There is a long bolt (10mm hex) that needs to be undone that supports the air con hoses to the block.  There is a spacer between the bracket and block that needs to be recovered also.

This bolt traps the belt on to the engine so must be removed.

This is the spacer, I’ve placed it back over the bolt.

Using a T60 bit turn the tensioner clockwise to release the tension off the old belt

Have a 4.5mm drill bit ready to insert to lock the tensioner.  If you look closely you can see a small hole on the tensioner arm just diagonally below and to the left of the end of my drill bit.  This is the hole in the tensioner that the drill bit goes thru and locks into a hole on the tensioner body nearer the top of the tensioner.

Turn the tensioner clockwise until you can get the drill bit engaged, you can see why you need the fan out the way!

Drill bit in place locking the tensioner so you can get the belt off.  A third hand is useful here!

The alternator has the smallest pulley and its easy to slide the belt off over the end of its pulley.

Feed the old belt off the crank pulley and the air con compressor.  It should just fall away.

Lift the belt from the engine bay.

Using an E12 (External Torx) socket undo and remove the tensioners retaining bolt.  This is tightened to 38Nm on re-assembly.  I used a new bolt sourced from BMW but it isn’t a stretch bolt so in theory should be good to re-use.

With a bit of careful wiggling pull the tensioner out of the block and between the hoses.  Note position of drill bit holding it locked.

Now for the idler pulley, it’s partially hidden behind that air con pipe bracket just to make life that bit more challenging.

Prise off the centre cap with a small flat screwdriver to expose its central fixing bolt.

I needed a long T50 bit to reach past the air con hose bracket

I used a foam matt inserted on the back of the radiator to protect the fins of the radiator while undoing it. 

Unscrew it from the block and lift it out.

Now the re-assembly can commence with the new tensioner being screwed back into the block…

…and tighten to 60Nm on re-assembly.

Insert the new tensioner.  It will only fit one way, note the locking pin holding the tensioner up so that there is room to install the new belt.

Tighten the tensioner to 38Nm.

Loop the new belt over the crank pulley and the air con compressor pulley.

Refit the air con hose bracket bolt and spacer, this ‘traps’ the belt on to the engine.

Clip on the idler pulley centre cap and feed the belt over the alternator

Get the T60 bit back out and turn the tensioner clockwise to allow you to take the factory supplied locking pin out and then gently turn it anti clockwise to tension up the belt.

Double check that the belt is correctly routed before re-fitting the fan and the upper cross brace, see links above for those jobs.

Mount your old tensioner in a vice so you can recover your drill bit.  On inspecting the old parts I removed, there was a bit of play and a grumble from the idler pulley bearings when spun up.  There was slightly less play in the tensioner pulley and its bearings were quieter.  It is important to replace all these parts at the same time as they wear at the same rate.