Maintenance Intervals
Unlike most BMW engines, the M20 engine uses a timing belt. The distributor guard plate is actually the upper timing belt cover.
WARNING
Timing belt maintenance is extremely important! M20 engines utilize an interference-type, non-free-wheeling engine. If the timing belt breaks, the valves in the cylinder head may strike the pistons, causing potentially serious (also time-consuming and expensive) engine damage. The normal recommended replacement interval for the timing belt is 50,00 miles (80,000 km), every 4 years.
The timing belt should be replaced on the M20 engine should be replaced as follows:
Every 4 yearsEvery other Service IIThe first service after 50,000 miles (80,000 km)Anytime removal is necessary to complete a repair
Removal & Installation
M20 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.
NOTE
At TDC of No. 1 piston compression stroke, the camshaft sprocket arrow should align directly on 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 on a 2 piece hub, hold the crankshaft hub from rotating and remove the crankshaft hub bolt.
- Install the hub bolt into the crankshaft about 3 turns and using a gear puller, remove the crankshaft hub.
- Remove the bolt from the engine side 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 in to remove the belt. Remove the intermediate shaft sprocket bolt and the sprocket.
- Loosen the oil pan bolts and remove the 3 front pan bolts that go into the timing cover. Use a thin blade to loosen the oil pan gasket from the cover. Remove the 6 bolts holding the cover and remove from the engine.
To install:
- Remove the oil pan and replace the gasket using non-hardening sealant at the joints. Replace the seals in the cover if damaged, worn or brittle. Install the timing cover using new gaskets and tighten the M6 bolts to 71-88.5 inch lbs. (8-10 Nm) and the M8 bolts to 15-17 ft. lbs. (20-24 Nm). Tighten the oil pan M6 bolts to 80-97 inch lbs. (9-11 Nm) and the M8 bolts to 13-15 ft. lbs. (18-22 Nm).
- Install the intermediate shaft sprocket and timing belt. Tension the belt.
- 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 287.6-317 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, then 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 and connect the negative battery cable.
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