Did the belt tensioner and pulleys today on my 07', 335i. I bought the belt tensioner kit from ECS Tuning for about $140.00. All the part were OEM supplier parts. You can pay an extra $50.00 for the ink it takes to put the BMW logo on the parts if you like, but I choose not too.
1) Jack up the car and take off the liner underneath the engine; you will need a 8mm socket
2) While you are under there you might as well take the one screw out that fastens the oil cooler to the fan.
3) Lower the car back down.
4) Take off the upper intake pipe that goes from the front of the car to the air box. You'll need a torx bit (there are two screws).
5) Unplug the fan and move the cord by undoing a few fasteners; move it over the left and out of the way.
6) There is one torx screw that holds the fan into place and it is located on the passengers side near the radiator.
7) Carefully lift the fan out of the engine bay. You may have to manipulate some items a little to lift it out, but for the most part it literally just slides up and out.
8) There is a lower intake pipe attached via bracket which is held to the engine via two torx screws just south of the vans solenoid(s). Undo both of those screws.
9) Follow the lower intake pipe to the drivers side of the engine and note where it can be taken apart via with a 6mm socket or a flat screw driver. Undo this pipe.
10) There is a charge pipe attached to the lower intake pipe; twist and pull it. Move it out of the way.
11) You should have some wiggle room now by being able to manipulate the lower intake pipe away from the engine.
12) Draw a picture of all the pulleys and then draw a line around the pulleys which represents the belt. You may want to just snap a picture with your smart phone. either or it doesn't matter.
13) Use a 60 Torx socket and an 18" breaker bar and place it in the large torx impression on the belt tensioner. If you have an 18" breaker bar, you don't need to be a muscle head as many DIY's state you need to be. The power of leverage in an amazing thing
14) Pull the breaker bar clockwise and move the belt off the tensioner pulley.
15) Proceed to take the belt off.
16) You will need a 45 torx socket and perhaps a 3" extension. A thin style ratchet helps here.
17) Undo the dust cap with a small flat screw driver on the belt tensioner and undo the one bolt which secures the belt tensioner to the engine. Take the belt tensioner out. Before you do this, make a mental note of how it looks in relationship to the pulleys and how it is north and south.
18) Undo the dust cap with a small flat screw driver of the upper pulley. Note the upper and lower pulley(s) are not the same size, so make a mental note of which one is bigger and smaller. Take out the upper pulley with the 45 torx socket. You probably won't have room for the 3" extension here.
19) Undo the dust cap with a small flat screw driver of the lower pulley. Take out the lower pulley.
20) Install the new lower pulley and torque it down to 30# plus a 90 degree turn. Put the dust cap on the lower pulley
21) Install the new upper pulley and torque it down to 30# plus a 90 degree turn. Put the dust cap on the upper pulley.
22) Install the new Belt Tensioner. DO NOT pull out the pin on the belt tensioner yet. Torque it down to 30# plus a 90 degree turn.
23) Install the belt; I went to the lowest pulley on the drivers side first and threaded it across to the crank. I then worked my way up to the top. Double check, TRIPLE check your picture / diagram of the how the belt loops around each pulley. Make sure the belt is firmly in the grove of each pulley that has a grove.
24) Now take your 18" breaker bar and 60 Torx socket and place it into the large torx impression in the tensioner.
25) Double check that each belt is on each pulley and that each grooved pulley is seated correctly in terms of the groves of the belt are in place.
26) You will need a set of pliers; put them on the pin located on the belt tensioner.
27) Pull on the breaker bar clockwise and pull the pin out. Be careful just to sort of gently wiggle it out. If you pull too hard, your recoil could end up putting a nice hole in your exposed radiator. That would suck because the radiator is all aluminum, which makes it about $450.00 give or take a $100.00. Once the pin is out release the breaker bar back.
28) Triple check the belts to make sure they are all in place. You may have to move the belt tensioner a back and move a part of the belt here or there.
29) Basically your done!!!!
30) Secure the lower intake pipe to the engine with the two torx screws and put the pipe back together on the drivers side with the 6mm socket or flat screw driver. Make sure you put the charge pipe back; push it into place and twist.
31. Make sure nothing is in the way of any engine parts etc. You can start the engine now and see if you did it right. Just because the fan in not in, does not mean you can't start the engine. NO you won't blow any codes either.
32. Let the engine run a little and rev it up over 2000 RPMS etc a few times. Observe and make sure the belt is rotating correctly without issue.
33. The next step is putting the fan back in. This can be a little tricky; it will not go in, often times, as easy as it went out. My best advice would be to jack up the car a little and then feed the fan back in top side as far as you can; it will not just slide back down. Go under the car and manipulate the lower pipes on the drivers side, it is stuck on. Once you do this it should come down a little more. Make sure the oil cooler is out of the way.
34. Go back up top side and wiggle it into place; eventually it will slide down the rest of the way. It will not go down unless you fan is level.
35. Plug it in and fasten the wire back into the little clips that run topside of the radiator. Put the one torx screw on the top passenger side back in. Go underneath the car and secure the oil cooler to the fan. Now you can put the protective cover back on with the 8mm socket. I like to put some de-greaser on the pan, soak it a little, hose it off and let it dry in the sun. I suppose that should be done right after you take it off and undo the oil cooler back in step 2.
36. Put the upper air intake pipe that directs air to the topside of the air box back into place with the two torx screws.