DIY: idler pulley replacement

If your car sounds like this its your idler pulley
YELLOW ARROW IDLER PULLEY 16mm bolt to remove the Pulley
RED ARROW TENSIONER 14MM BOLT and push down to remove the tension so you can remove the belt.


STEP 1: remove the intake


STEP 2: remove the radiator fan only one screw on the fan upper left if your facing your engine then slightly pull the fan. Make sure to unplugged the fan and move any thing thats blocking the way the only tough part is to move the radiator hose just slowly pull it out again move anything thats blocking and u dont have to take anything off

STEP 3: take the cover off the pulley tentioner and get a 14mm socket and push down. It will move the tensioner so u can remove the belt... This is not the idler pulley its the one on top of that pulley


STEP 4: 16mm socket to remove the idler tensioner and replace


STEP 5: put everything back and done

Would have taken 30 minutes but i took my time

Thanks for the write up! I used it to start my idler pulley change, but ran into a significant problem.

The pulley you have in your photo, BMW part #11287841228, has an off-center bolt hole and is only compatible with M3's built before 4/29/08. See here for details. For production dates of 4/29/08 and newer you will need a pulley with a centered bolt hole, BMW part #11287841531.

This stationary idler pulley is also referred to as a "deflection pulley."

Production date up to 4/29/08 on the left, 4/29/08 or later production date part on the right:





Another thing to consider is that the hoses that run below the fan shroud are clipped onto the fan shroud to hold them in place. As you pull up on the fan shroud some of them will not want to come loose easily. You can carefully try to reach below the fan shroud with one hand to loosen or remove them. When you are re-installing the fan shroud you can skip the step of clipping the hoses back in place and with a little luck, you will probably never have a problem, but it's not recommended. I couldn't find a way to re-clip those hoses back into place without removing the belly pan cover below the car. The next time I do this job I'll start by taking off the underbelly cover and unclip the hoses from the fan shroud to start with. Here are some of the clean clip marks on the hoses below. I believe there were two additional clips to the right just out of the photo.

Nice to see this. It's getting close to belt change time for me

This DIY really helped.

My M3 was built in Feb 02, so I made sure I had the right idler pulley. (Thanks, Theodore!)

While I was at it, I also replaced:

the accessory belt
the accessory belt tensioner
the accessory belt pulley
the A/C Belt
the A/C belt pulley
and the A/C belt Tensioner

ECS tuning part #2777259

BTW, you can get away with not replacing these, (except the belts) when you start hearing that squealing from under the hood (mine started around 85K miles) it'll be the idler pulley. I've always believed that you should replace parts that'll liable to go bad while you are at it. The pulleys all run on bearings, so they will wear out at some point.

I couldn't get the accessory (alternator) belt off without removing the idler pulley. Perhaps someone knows a better way?

The tensioners and pulleys are 14mm bolts, less the idler pulley.

Those bolts are not on super tight, so make sure you don't wrench them down too tight.

Remember there are rubber bushings that can be crushed.

Be super careful of the radiator overflow hose. The nipple on the upper radiator breaks easily.

The hardest part to removing the fan housing is getting it past the upper radiator hose. Be patient, be careful, and you can get the housing out without breaking anything. (I didn't)

+1 for removing the underbelly cover. Not only does it make it easier to reattach those lower hoses, but also to retrieve those dropped parts/tools.



edit - Just noticed that the picture below is wrong. The A/C / Power Steering Belt goes OVER the Power Steering pulley (#3), not under. It also goes UNDER the Idler pulley (#5), not over. See the pic below.

edit edit - So, ECS sent me the wrong belts. The correct belts for my pre-May 2008 are 6PK1067 and 6PK1460



jfirwin wrote

This DIY really helped.

My M3 was built in Feb 02, so I made sure I had the right idler pulley. (Thanks, Theodore!)

While I was at it, I also replaced:

the accessory belt
the accessory belt tensioner
the accessory belt pulley
the A/C Belt
the A/C belt pulley
and the A/C belt Tensioner

ECS tuning part #2777259

BTW, you can get away with not replacing these, (except the belts) when you start hearing that squealing from under the hood (mine started around 85K miles) it'll be the idler pulley. I've always believed that you should replace parts that'll liable to go bad while you are at it. The pulleys all run on bearings, so they will wear out at some point.



Agreed, you should replace the belts and tensioners at the same time. Belts and tensioners have a finite life, and may be getting stressed if the idler pulley is on its way out.

I don't know what the change interval for those belts is, but 60-90k seems typical for most vehicles.

dparm wrote  

jfirwin wrote

This DIY really helped.

My M3 was built in Feb 02, so I made sure I had the right idler pulley. (Thanks, Theodore!)

While I was at it, I also replaced:

the accessory belt
the accessory belt tensioner
the accessory belt pulley
the A/C Belt
the A/C belt pulley
and the A/C belt Tensioner

ECS tuning part #2777259

BTW, you can get away with not replacing these, (except the belts) when you start hearing that squealing from under the hood (mine started around 85K miles) it'll be the idler pulley. I've always believed that you should replace parts that'll liable to go bad while you are at it. The pulleys all run on bearings, so they will wear out at some point.



Agreed, you should replace the belts and tensioners at the same time. Belts and tensioners have a finite life, and may be getting stressed if the idler pulley is on its way out.

I don't know what the change interval for those belts is, but 60-90k seems typical for most vehicles.

I didnt change my belt when i replace the oulley thats because when i took out the belt it was almost the same condition as the new one i bought just dusty so returned the belt i bought... Also i was at 95k miles at the time of change

Hello guys... I don't understand how the belt should goes?

Under or over Power Steering?

What picture is RIGHT? Picture of engine or scheme picture?

RomanK wrote

Hello guys... I don't understand how the belt should goes?

Under or over Power Steering?

What picture is RIGHT? Picture of engine or scheme picture?

BMW used both belt routings. One is for early cars, through the middle of 2008, and one is for later cars. I think the photograph of the motor is the early car and the diagram of the pulleys and belts is the later car. I think the belt that runs the AC and PS is two sided on the later cars, and one sided on the early cars.

pbonsalb wrote

BMW used both belt routings. One is for early cars, through the middle of 2008, and one is for later cars. I think the photograph of the motor is the early car and the diagram of the pulleys and belts is the later car. I think the belt that runs the AC and PS is two sided on the later cars, and one sided on the early cars.

Correct: For M3's built before 4/29/08 the belt is routed over the (clockwise turning) power steering pump (and under the idler pulley). M3's with build dates after 4/29/08 the belt is routed under the (counter-clockwise turning) power steering pump (and over the idler pulley). This is because they changed the idler pulley design (see above posts for part numbers and pictures).

*Note: There are some E9X M3s out there with a replacement engines that may not meet the criteria above. Probably worth taking a look before you order just to be sure.

I have an early 2008 m3 and that fan shroud is a pain to remove. The clips on the left and right sides of the shroud get hung up on the radiator hose connections. I do have the hoses unclamps. Any tips?

Figured it out. You have to move the right side of the shroud out first before the left. Then it just comes out. Also the idler pulley (not tensioner) can be swapped without removing the fan shroud if you have small hands.

Is there an official maintenance requirement to replace certain belts and tensioners?

I have an squeal after cold starts and I need to replace the idler pulley. Not sure if there's other related maintenance items to do while I'm in the that general area.

Flying Ace wrote

Is there an official maintenance requirement to replace certain belts and tensioners?

I have an squeal after cold starts and I need to replace the idler pulley. Not sure if there's other related maintenance items to do while I'm in the that general area.

Let me know if you find someone to do it, I have the same problem. I already bought the pulley but don't feel like doing it myself. In general, you can replace all the belts, tensioner pulley, tstat, tstat sensor, water pump. But it's kinda pricey...

monterey wrote

Let me know if you find someone to do it, I have the same problem. I already bought the pulley but don't feel like doing it myself. In general, you can replace all the belts, tensioner pulley, tstat, tstat sensor, water pump. But it's kinda pricey...

my go to M3 shops are all in the East Bay...

My X5 had one service done at Holland Car Care in Burlingame. Pricey...

Flying Ace wrote

Is there an official maintenance requirement to replace certain belts and tensioners?

I have an squeal after cold starts and I need to replace the idler pulley. Not sure if there's other related maintenance items to do while I'm in the that general area.

I'm doing these now, not because of symptoms but because this is my 5th BMW and I know better than to wait for them to age out. My car is a March 2008 build with 89,8xx miles on it. THe tensioners and pulleys seem fine as they come off, but the idler bearing on the PS/AC belt is in rough shape, really gravelly sounding compared to the new pulley. And obviously the belts at 90,000 miles while they may look fine are certain to be nearing the end of their realistic service life, and lately everything plastic that gets hot that I touch on my car has been pretty brittle unless warmed up first lately so I'm glad I'm doing it.

Pro tip: If you're dumb like me and don't take off the water pump pulley to do the main accessory belt tensioner TAKE YOUR TIME WITH THE TENSIONER TO BLOCK BOLT. I scared the shit out of myself before I realized I didn't have it threaded in at all and thought I had bought myself a timesert job on a $1$,$$$ engine block. With the water pump pulley off it'd be trivial but it's a fishing expedition to get it back in there and threaded with it on.

Another pro tip: TApe off the upper radiator support so you don't mangle your forearms on the sharp edge of the plastic. Or, you know, wear long sleeves.

And final pro tip: Cut a piece of cardboard and blue tape it in place between the radiator and the engine so you don't bend fins/skin knuckles when you drop tools:tensioner/beers. Glad I did.

Flying Ace wrote

Is there an official maintenance requirement to replace certain belts and tensioners?

I have an squeal after cold starts and I need to replace the idler pulley. Not sure if there's other related maintenance items to do while I'm in the that general area.

I can't find an official change interval for these, which is rather odd. On both of my previous Audis, most of us did it at 60k. You can't really visually inspect the parts to see if they need to be replaced (short of the belt already being shredded).

The ones I just pulled out Both tensioner pulleys had some wear but the bearings on them seemed in ok shape and tensioners themselves seemed ok. The main acc belt tensioner pulley had the most wear with a lip on either side of where the belt ran that would catch your fingernail. This is after 90000 miles nearly. Probably wasn't necessary except the idler but you know, bmw

Guys, i just did Pully and Ac compressor replacement with new belt but i don't know how to put it back the belt(( i wasted over and an hour and gave up, what's the easiest way to do it?

Herofmine wrote

Guys, i just did Pully and Ac compressor replacement with new belt but i don't know how to put it back the belt(( i wasted over and an hour and gave up, what's the easiest way to do it?

Place a 14mm box end wrench (or a socket w/ratchet as a second best choice) on the bolt in the center of the tensioner pulley (for reference, its the pulley where the red arrow in the picture in the very first post of this thread points to). Push the tensioner pulley downwards and and hold it there with one hand while you slip the belt into place. Then slowly let the tensioner pulley back up to put pressure back on the belt. Skip ahead to 15:28 in this video and you can see the guy do this:

It was easier for me to slip the belt over the idler after I got it pre positioned on all the other pulleys, including tensioner, first. Spent about 10 minutes banging my head against the wall trying to slip it over the tensioner pulley before I figured it out

Theodore wrote

Herofmine wrote

Guys, i just did Pully and Ac compressor replacement with new belt but i don't know how to put it back the belt(( i wasted over and an hour and gave up, what's the easiest way to do it?

Place a 14mm box end wrench (or a socket w/ratchet as a second best choice) on the bolt in the center of the tensioner pulley (for reference, its the pulley where the red arrow in the picture in the very first post of this thread points to). Push the tensioner pulley downwards and and hold it there with one hand while you slip the belt into place. Then slowly let the tensioner pulley back up to put pressure back on the belt. Skip ahead to 15:28 in this video and you can see the guy do this:

Thanks a lot! It was easy! Lol

Nice Write-up, adding to my list of shit to do.