BMW (Bavarian Motor Works) began as an aircraft manufacturing company in Munich, Germany in 1910. The company started manufacturing vehicles in 1928. Known for luxury and reliability, BMW continues to impress drivers with its line of cars and SUV's. In the 1970s, BMW introduced a three-tier sports sedan line -- the 3-series, 5-series and 7-series -- that featured performance engines starting with the letter "M." M40 engines can be found in both the 3-series and 5-series vehicles.
Purchase a timing belt specifically for BMW M40 engines from an auto parts store or online. Lift up the bonnet and disconnect the negative battery cable. Remove the following to reach the upper timing belt cover: distributor cap and rotor, inner distributor cover and seal, distributor guard plate attaching bolts and nut, rubber guard and guard plate. Refer to the vehicle owner's manual or service guide to correctly identify these parts.
Locate the crankshaft and turn it to set the No. 1 piston to Top Dead Center (TDC) of the compression stroke.
Locate and remove the radiator, lower splash guard, alternator, power steering and air conditioning belts, crankshaft pulley and vibration damper. Use a wrench to keep the crankshaft hub in place to remove the crankshaft hub bolt. Remove the wrench and the crankshaft hub.
Locate the alternator bracket and loosen the adjusting bolt that holds it in place. Move the bracket to the side. Remove the TDC transmitter and the lower timing belt cover. Loosen the tensioner pulley bolts and push the tensioner pulley bracket to the side. Use a piece of chalk and draw an arrow to mark the running direction of the timing belt before removing it from your vehicle.
Align the timing mark on the crankshaft sprocket so it points at the notch on the front engine cover. Locate the camshaft sprocket mark and make sure it points to the mark on the cylinder head. Install the new timing belt. Tighten the belt by turning the crankshaft bolt located on the engine using a wrench. Move the tensioner pulley bracket back to its original position and tighten the tensioner pulley bolts.
Reattach the lower timing belt cover and TDC transmitter. Move the alternator bracket back to its original position and tighten the alternator adjusting bolt. Reattach the crankshaft hub and the crankshaft hub bolt. Reattach the crankshaft pulley and vibration damper, power steering and air conditioning belts, alternator, lower splash guard and radiator.
Reattach the upper timing belt cover. Reattach the rubber guard and guard plate, distributor guard plate and nut, inner distributor cover and seal, distributor cap and rotor. Reconnect the negative battery cable. Start the engine to make sure the timing belt is installed properly.
Keep all parts separate after removal for easier reattachment after changing the timing belt.
Wait until your vehicle's engine is completely cool before changing the timing belt. Failure to wait until the engine is cool may result in bodily injury.