REMOVAL & INSTALLATION M20 Engine
See Figures 1, 2, 3 and 4
The M20 engine is the only engine covered in this guide that is equipped with a timing belt as opposed to a timing chain. A timing belt has the advantage of being a quieter method of driving the camshaft as compared to the timing chain. The disadvantage is that the timing belt must be changed on a regular basis, or risk having the belt break and causing severe engine damage. If the belt breaks, the valve timing will be off compared to the piston timing. This will cause the valves to hang open and contact the pistons on the next engine revolution. Bent valves, damaged pistons and major engine repair is the result of ignoring timing belt changes.
BMW recommends that the timing belt be changed every second Inspection ii, or every 4 years on cars that have low mileage. Most of the rest of the industry has timing belt changing intervals ranging from 40,000 miles to 60,000 miles. It is better to change the belt at a lower mileage than at a higher number.
The timing belt must be replaced every time the belt tensioner is loosened. Do not reinstall a used belt. Reusing a timing belt, even one with low mileage, is not worth the chance of having a belt break and damaging the engine.
- Disconnect the negative battery cable. Remove the distributor cap and rotor. Remove the inner distributor cover and seal.
- Remove the 2 distributor guard plate attaching bolts and one nut. Remove the rubber guard and take out the guard plate (upper timing belt cover).
- Rotate the crankshaft to set No. 1 piston at tdc of its compression stroke.
At tdc of No. 1 piston compression stroke, the camshaft sprocket arrow should align directly with the mark on the cylinder head.
- Remove the radiator.
- Remove the lower splash guard and take off the alternator, power steering and air conditioning belts.
- Remove the crankshaft pulley and vibration damper.
- If equipped with a 2 piece hub, hold the crankshaft hub from rotating with the proper tool. Remove the crankshaft hub bolt.
- Install the hub bolt into the crankshaft about 3 turns and use the proper gear puller, to remove the crankshaft hub.
- Remove the bolt from the engine end of the alternator bracket. Loosen the alternator adjusting bolt and swing the bracket out of the way.
- Lift out the tdc transmitter and set it aside.
- Remove the remaining bolt and lift off the lower timing belt protective cover.
- Loosen the timing belt tensioner roller bolts and push the roller. Tighten the upper bolt with the roller pushed in. Remove the belt.
- Check the alignment of the mark on the camshaft sprocket with the mark on the cylinder head. Check that the crankshaft sprocket mark aligns with the notch in the timing case.
- Install the new timing belt by starting at the crankshaft sprocket and continuing in reverse direction of engine rotation.
- Loosen the upper timing belt tensioner roller bolt. The spring tension should be enough to move the roller. Turn the engine 1 revolution in the direction of rotation using the crankshaft bolt to tension the belt. Check that the timing marks align exactly at the camshaft sprocket and the crankshaft sprocket. Tighten the roller bolts, top bolt first, then the bottom bolt.
- Install the lower timing protective cover and tighten the bolt. Install the tdc sender.
- Replace the alternator bracket. Install the crankshaft hub and torque the nut to 281-309 ft. lbs. (390-430 Nm).
- Install the vibration damper and pulley. Torque the bolts to 17 ft. lbs. (23 Nm).
- Install the upper cover and nut. Install the rubber guard. Check the condition of the O-ring and install the upper cover. Install the rotor and distributor cap.
- Install the accessories and belts. Install the splash shield and fill the cooling system with coolant mixture. Bleed the cooling system.
- Apply a sticker showing the date and mileage of the belt change on the engine.