M20 Timing Belt


Cost: less then $60


The older E30 325i and the older ('89-90) 525i have the M20 engine with the timing belt.
This timing belt and its tensioner should be changed every 70,000 km

Oil timing belt or cracked one.
Time to change it

  • BMW coolant + distilled water
  • Torque wrench
  • Timing belt
  • Tensioner
  • All the belts while you are at it
  • Camshaft seal
  • Gasket remover tool and spray

Water pump, hoses, belts, thermostat

1. Following the Bentley manual procedure page 118-1.
2. Loosen the bolts on the waterpump pulley, remove all the belts, best time to change all of them. Remove the fan clutch (32mm wrench and don't forget that the threads on the fan clutch are left hand threads). Remove the radiator shroud.
3. Remove the 10mm bolts on the waterpump pulley and remove the pulley.
4. With the engine cold, remove the plug from the bottom of the radiator and the bolt below cylinder #6 on the engine block to drain the coolant. You can remove the hoses and change them if you want.
Remove the metal hose that you can see on the picture #3. It is attached with two bolts on each side.
5. Remove the distributor cap cover, distributor cap and rotor
Remove the bracket from the alternator to the upper timing belt cover (upper bracket). Remove the bolts from the timing belt cover and remove it.
6. Using a 22mm socket, rotate the crankshaft clockwise until the engine is at Top Dead Center. You have to line up the marks on the cylinder head with the mark on the camshaft pulley. (See picture on the Bentley manual.)
7. Remove the 6 bolts that holds the lower pulley then remove the 22mm bolt and the pulley. You can now remove the last bolts on the lower timing belt cover and remove the cover.
8. Image from the top
9. Remove the bolt in the center of the camshaft pulley. Loosen the upper bolt that holds the tensioner. Loosen the tensioner lower bolt at the base of the long stud.
Using a screwdriver, push the tensioner from the top to release the tension then tighten the upper bolt. Remove the timing belt.
10. Remove the camshaft pulley then the two bolts holding the camshaft seal cover.
10. Remove the cover then remove the old seal without damaging the cover, clean everything.
11. Part# for the different seals
12. You can remove the water pump while you are at it and clean everything in the process.
13. Doesn't that look better??? Change the tensioner, put the new one in place, (noticed that the tensioner is all the way to the left). Install the camshaft pulley then make sure that the camshaft pulley marks match the marks on the cylinder head. Make sure that the mark on the crankshaft hub aligns with the one on the engine. (See Bentley picture).
14. Install the new timing belt beginning with the crankshaft pulley in a counterclockwise direction without slack. All the belt slack should be at the tensioner. When the belt is in place, slowly loosen the upper bolt of the tensioner to tighten the belt.
Using the crankshaft 22mm bolt, turn the engine for two full revolutions until the marks match again. Make sure that the camshaft pulley marks are aligned along with the marks on the crankshaft hub.
If everything is right, torque the upper then lower tensioner bolt (16 ft-lb). Time to reinstall everything with new belts.
Be very careful with the crankshaft position sensor (CPS), if the cable isn't where it is suppose to be, it will be cut by the waterpump pulley... Then you are going to spend a lot of time on diagnostic, why the car doesn't start... if this piece is broken, the car will NEVER start.

Add 50% BMW coolant and 50% distilled water then bleed the cooling system. All done, if you didn't do any mistakes, the car should start right away... else, you might have a major problem on your hand.

Another thing to pay attention to: the hose that is behind the metal bracket, make sure that it is attached with the OEM clamp to the bracket Mine wasn't and it touched the cooling fan, until a leak appears... at 400 miles from my house... (A hose that looked the same was put into place and I was able to go back home).


- Home of the Bmw 518i, 520i, 524td, 525tds, 525i, 535i, 530i, 540i, M5 and other Bmw E34 chassis -