How to Replace the Belts on a BMW 325i

1. Disconnect the negative cable from the battery. The negative cable is black.
2. Remove the bolts holding the black plastic splash shield underneath the car. Remove the shield. Open the lid for the coolant tank. Drain coolant from the block into a container by removing the drain bolt under the exhaust manifold. The exhaust manifold is located on the passenger side, behind the oil filter.
3. Grab a 32-mm side open-end wrench. Use this to remove the cooling fan from the water pump by turning the nut clockwise to remove it. Once removed, keep it stored in an upright position and remove the fan shroud by unclipping the two clips that hold it on. Remove the coolant hoses from the radiator and water pump. Remember which hose goes where for when you put them back on.
4. Remove the two mounting bolts that are holding the radiator in place. Remove the radiator. Remove the three bolts that are holding the distributor cap in place and then remove the cap. Loosen the three screws that are holding the rotos in place and remove the rotor. There will also be a dust shield underneath the rotor that you need to remove as well.
5. Find the four 10mm bolts that are holding the water pump in place and loosen them. Find the six 13mm bolts holding the crank pulley in place and loosen those as well. Loosen and remove the belts for power steering, air conditioner and alternator and water pump.
6. Remove the water pump bolts and the pump itself. Finish removing the crank pulley bolts and the crank pulley itself. There is something called a harmonic damper located behind the pulley that you need to leave in place.
7. Remove the three bolts holding the upper camshaft cover in place. Use a 22mm socket and ratchet on the crankshaft nut and turn clockwise until the mark on the sprocket lines up with the notch on the head. The mark sometimes looks like an arrow or an indent. Also, make sure that the 'O/T' mark on the harmonic damper lines up with the notch on the lower timing belt cover. If these timing marks are not aligned, the process will not work successfully.
8. Continue to remove the crankshaft damper. Remove the bolts holding the lower camshaft cover into place and loosen the top bolt for the timing belt tensioner pulley. Loosen the lower bolt as well and rotate the tensioner towards passenger side of the car. Then, tighten the upper bolt back.
9. Slide the timing belt off of its pulleys and turn the sprockets clockwise, starting at the camshaft sprocket. Remove the top tensioner bolt, guide pin and spring. Remove the lower bolt as well and the tensioner. Install the new timing belt tensioner pulley. Hand tighten the lower bolt and install the guide pin and spring. Rotate the pulley towards the passenger side and loosely put in the bolt. Push the pulley all the way towards the passenger side and tighten the bolt.
10. Adjust the timing marks if you need to to make them line up. Install the new timing belt. Work in a clockwise direction and make sure to keep it tight between each sprocket. Loosen the upper tensioner bolt until the tensioner rotates to the driver's side. This will engage the timing belt.
11. Install the lower timing cover and harmonic damper. Make sure that the timing belt marks line up by rotating the crankshaft with the socket two full turns. If they do not align, you need to remove the belt and install it again until the lines match up.
12. Tighten the upper and lower tensioner pulleys and bolts. Reinstall camshaft cover, water pump, belts, radiator and fan belt. Reinstall the distributor cap and rotor and radiator hoses. Plug the drain in the block and top engine off with coolant. Reinstall splash shield.