How to Change the Accessory Belt Tensioner Pulley on a BMW 323I

1. Park the BMW 323I and turn the engine off. Set the parking brake and open the hood. Wait for the engine to cool down before working inside the engine compartment.
2. Inspect the top of the fan shroud and locate the accessory belt routing diagram. The diagram shows the proper routing instructions for the accessory belt. If the routing diagram is not stamped to the fan shroud, it will be stamped to the underside of the hood.
3. Stand in front of the engine and locate the accessory belt tensioner. The tensioner and pulley are located on the front-center of the engine. Locate the black plastic cover in the center of the tensioner pulley. Pry the plastic cover off the center of the tensioner pulley with the tip of a flat-head screwdriver. This will give you access to the hex head hole located inside the tensioner pulley. Place the cap in a safe area.
4. Slide an 8 mm hex-head socket onto the end of a 3/8-inch drive breaker bar. Insert the 8 mm hex head socket into the hex head hole located inside the tensioner pulley. Turn the breaker bar clockwise with one hand to loosen the tension from the belt. Slide the belt off the tensioner pulley with the other hand. Slowly release the tensioner and remove the breaker bar.
5. Hang the belt from one of the top engine accessories with a bungee cord to prevent the belt from slipping out of the accessory pulleys while the tensioner is being replaced.
6. Locate the mounting bolts that secure the tensioner to the front of the engine. Loosen and remove the mounting bolts from the tensioner with a ratchet and a socket. Place the bolts in a safe place. Pull the tensioner off the front of the engine with your hands.
7. Pry the plastic center cap off the new tensioner pulley, if needed to expose the hex-head hole. Position the new tensioner onto the same area of the engine. Match up the tensioner's mounting holes with the holes on the front of the engine. Screw the mounting bolts into the tensioner until the bolts are tight. Finish tightening the bolts with the ratchet and socket. Torque the tensioner mounting bolts between 25 and 30 foot-pounds with a torque wrench and a socket.
8. Place the hex-head socket and the breaker bar onto the new tensioner pulley. Turn the breaker bar clockwise with one hand. Remove the bungee cord with the other hand and slide the belt under the new tensioner pulley. Slowly release the tensioner and remove the breaker bar. As the new tensioner is retracting, it will bring the belt to the proper tension. Snap the plastic cap back over the front of the tensioner pulley.
9. Inspect the belt to ensure that it has remained seated on the inside of all of the accessory pulleys. Use the belt routing diagram to re-route the belt around the pulleys, if needed.
10. Crank the engine and inspect the belt to ensure that it remains seated inside the pulleys. Inspect the new tensioner to ensure that the tensioner pulley is moving up and down freely, with no restrictions, while the belt is traveling under it. Let the engine run for about 30 seconds and then turn the engine off. Close the hood.