Tuesday, March 3, 2009

Changing Belts on the BMW E34-M50 Motor (525i)

The M50 motors use two drive belts to power all of the accessory stuff on the motor. The larger belt, which has to be installed first is driven by the crank pulley and drives the Fan/Water pump, the alternator and the Power steering pump. There are two other pulley's that are in this system also, one is the actual tensioning pulley and the other is an idler pulley. To change this side's belt, the only thing you really need to know is which one is the tensioning pulley.

Here is a picture of the routing of the belt on this side:

The arrow I've drawn is the location of the tensioning pulley. Depending on your tensioner, you will either use an allen wrench or a regular wrench or socket to take the tension off the belt.

Once you've determined what you need, you turn the wrench clockwise (oriented with you facing the front of the car) or to put it another way, turning the wrench towards the drivers side of the car. Once you've done this, the tension should be loosened and you can slip the belt off of the pulley. I've done this so many times now, I can do it in my sleep. Installation is reverse of removal.

One other thing for this side, it can be done with the Fan and Shroud installed, but to save yourself some time and frustration, it is much easier just to remove the Fan and Shroud.

The other side is also driven by the crank pulley, however, it only drives the A/C Compressor. There is only one other pulley there and it is the tensioning pulley. On both of my 525i's, you use an allen wrench to un-tension the belt. This side is the same, clockwise takes the tension off the belt. This belt goes on last due to the way the crankshaft pulley is set up. If you just have to replace this belt, you don't have to remove both belts.

Good Luck!


Anonymous said...

Thanks for the writeup. Saved me alot of time since I never worked on a BMW till I got overseas.

Almost Gone said...

You are very welcome, I'm glad to be of service.

Anonymous said...

Thanks, as I had fogotten the belt routing due to the delay in chasing the water pump and thermostat parts.
My 1995 E34-M50 uses a T-50 Torx in the 2 tensioners rather than an allen wrench. The job is much easier if you take off the shroud and fan blade assembly.

Fullerton, CA

Almost Gone said...

Pete, it appears that you made this comment a while back. I just received it today.

Sometimes blogspot is a bit clunky.

Thanks for your comment. I didn't know that the Torx was used in those applications.


robert said...

Hi having a problem taking off the alt belt tensioner pulley disintegrated any tips cant get to lower bolt thanks rob

Almost Gone said...

@ Robert... Did the pulley disintegrate or the mount? If it's just the pulley, you should be able to still pull it off. If it's the mount, I'm not sure exactly what you'd need to do. If you want to email me a bit more detail, perhaps I can help. Here is my email: station75@gmail.com