What many E30 owners with m20 engines (325, 325e, 325es, 325i, 325is, 325ix) might not know is that one of the most important maintenance steps after acquiring an E30 is to replace the timing belt and water pump if you do not know when the last time it was changed, or even slightly unsure (dont take the sellers word). Why? Because the engine is an interference engine, which means if your timing belt snaps the pistons will hit the valves and thats that for your engine. The recommended interval to replace by BMW specifications is every 60,000 miles or 100,000 kilometers.
Note: this is not exclusive to the m20 engine family, most cars nowadays have interference engines, on the off time some cars will have non- interference (or also known as free running) engines and if a belt snaps nothing bad happens you slap a new belt on and call it a day.
With the job costing about ~$1000 if you pay someone else to do it, most e30 owners as-they-should choose to do it themselves. If you dont have a Bentley publications manual already do yourself a favor and pick one up, it has step by step instructions on how to do virtually everything on your specific model (cheapest is to get it off ebay you can use the search function on the right).
1. First I would advise taking the hood off, mark the hinges with a method of your choice because you will need those markings when putting the trunk back on to make it align with the body panels. Also you will need to disconnect the windshield washer fluid hose and ground cable.
2. Drain and remove the radiator, and drain the block of coolant (draining the block is not required). First undo the bolt at the bottom of the radiator and let the fluid drain (bottom drivers side). Then undo the 19mm bolt to drain the coolant from the block:
The proceed to disconnect all hoses connected to the Radiator and undo the two bolts holding it in place, lift up and out of the car.
Radiator out of the e30:
3. Remove the Fan and fan clutch assembly. 32mm and turn in a clockwise direction because the bolt is reverse threaded. Break it free by taping your wrench with a hammer of sorts (rubber or soft is the best). Keep the fan/clutch assembly in an upright position once it is out so the fluid doesnt leak.
4. Remove cap and rotor by following your spark plug wires to the front of your car where they connect to the distributor cap and then the rotor behind it.
5. Remove the fan belts by loosening the star like bolts to put slack on the belts until you can take them off, on the alternator and power steering pump.
6. Remove the spark plugs because this will eliminate any compression in the cylinders so you can rotate the engine by hand.
7. Take off timing belt cover:
8. Rotate engine until it is top dead center:
8. Loosen tensioner bolts (dont remove) the bottom is a 15mm that is also used by the alternator, rotate the tensioner to the passenger side with a screwdriver to loosen tension on the belt (compress spring), and take the timing belt off.
Now depending on what all your replacing this is the perfect time to replace the water pump, and a good time to replace the tensioner too (same effect as the timing belt breaking).
Installation is reverse of removal.