Learning how to replace a 1993 BMW 525i's head gaskets is a procedure for a competent DIY mechanic. Make sure you have the correct tools and the correct head gasket for your BMW 525i before you begin.
- Service jack
- Axle stands
- Socket set and wrench
- Assorted screwdrivers
- Zip ties
- Start the engine and remove the fuel pump fuse. Allow the engine to cool and remove the hood completely, disconnect the negative battery terminal and drain the cooling system by removing the lower radiator hose.
- Jack up the BMW and rest the front on axle stands. Remove the two exhaust bolts holding the exhaust manifold onto the exhaust system. Lower the car to the ground.
- Remove the air filter and piping, the upper radiator hose and disconnect the oil dipstick tube from the thermostat. Disconnect the coolant temperature sensor.
- Label the HT leads and remove them from the spark plugs. Remove the distributor water shield and distributor cap.
- Loosen and remove the two 15mm bolts from the air conditioning unit (if fitted), the alternator bracket and the temperature sender unit from the wiring harness.
- Remove the plastic timing belt cover and the valve cover which has ten screws.
- Disconnect the throttle body wiring harness, the throttle cables, the throttle body and the vacuum lines.
- Disconnect the fuel lines which should now be unpressurized.
- Disconnect the throttle position sensor and zip tie them out of the way of the cylinder head.
- Remove the earth cable which is attached to the firewall with a 15mm bolt.
- Remove the heater hose and the brake booster vacuum hose.
- Zip tie the timing belt to the crankshaft pulley and remove the pulley bolt. Raise the pulley and secure it with rope to keep the timing belt from skipping a tooth.
- Remove the head bolts from the center outwards in a crisscross fashion. Having an extra pair of hands to lift the cylinder head off is recommended as it will be heavy. Use a straight edge to check the head for any warping. If there is warping or you aren't sure, it is best to have the head skimmed so that it will create a good seal. Clean the head face and block with brake cleaner and make sure nothing falls into the cylinders.
- With the surfaces ultra clean, carefully lower the head onto the block. Some find it easier to fit a thin, firm object (i.e. a pencil) into the water jackets so that they line up perfectly.
- Install the head bolts slowly and from the center outwards. Only tighten them as per the manufacturer's guidelines. For example, tighten a ¼ turn per bolt until all are the same, then go over the procedure until it is time to torque them up to the correct setting use a torque wrench.
- Fit gasket sealant to the valve cover surface after you have made it oil free. Refit all of the remaining parts as per the removal sequence.
- Reset the timing back base settings and use a timing light to set it correctly.