Checking and replacing spark plugs (BMW 5 Series E34)

Special tool required:

• A spark plug wrench, included in the on-board tool kit or available commercially.
• Additionally, it is recommended to purchase special pliers, such as HAZET 1849, which make it easier to remove spark plug tips.

The following wearing parts must be purchased:

• Spark plugs of the recommended type.

Spark plugs should be replaced every 20,000 km. Platinum spark plugs generally have a longer service life. They should be replaced when the central electrode is no longer visible in the insulator leg.

Removal

Only 520i/525i models produced since May 1990. (four-valve engines)

Remove the oil filler cap.



Remove the caps from the mounting bolts, unscrew the two bolts located under the caps. Remove the cylinder head cover.



Remove the connectors from all ignition coils by moving the connector brackets away.





Loosen the mounting bolts of all ignition coils and remove the ignition coils.

Note: There are ground jumpers on the ignition coils of the 3rd and 6th cylinders. When installing them, they should be screwed into the same places.

Remove all the sowing tips, pulling not by the wire, but by the tip. The mentioned pliers make removal easier.

Blow out the spark plug recesses in the cylinder head with compressed air to prevent dirt from getting into the threaded holes when the spark plugs are removed.

Using a special spark plug wrench, remove all spark plugs.

Inspect the spark plugs. With some experience, you can tell how the engine is running by looking at the spark plug.

Table 1



Check the spark plug insulators for leakage currents. Leakage currents leave thin, uneven marks on the surface. If traces of leakage currents cannot be completely removed, replace the spark plug.



Clean the spark plugs with a brass brush or sandblast.

Installation

All engines except four-valve: Check the interelectrode distance using feeler gauges. Specified value: 0.7-0.8 mm. On new spark plugs, the interelectrode distance is usually set correctly.

If it is necessary to bend the central electrode at a right angle to compensate for burning.

To adjust the distance between the electrodes, bend the ground electrode. There is a simple, practical tool for this, in the absence of which you can lightly hit the electrode from the side. When bending, rest a small screwdriver on the edge of the spark plug thread, but not on the central electrode, so as not to damage it.

Clean the threads on the spark plugs and in the cylinder head.

Screw the spark plugs into the cylinder head by hand until they stop.

Caution: Do not allow the spark plugs to become tilted.

Tighten the spark plugs to 25 Nm.

Attention: If you do not have a torque wrench available, then you must turn the candle with a flat seat A with the candle wrench approximately 90° (¼ turn. Candles with a conical seat should be rotated approximately 15 degrees, as well as used candles with a flat seat. If the spark plugs are too tight, they may break off when they are turned out, or the threads in the cylinder head may be damaged. In this case, it is necessary to repair the candle holes using UTC or Heli-Coli inserts.

Connect the spark plug caps in accordance with the firing sequence 1-5-3-6-2-4.

Check the reliability of the spark plug caps by rocking them.

Four-valve engines: Install the ignition coils and housings. Installation is performed in the reverse order. Check the reliability of the connectors and ground jumpers.

(Examine the original source using the link on the website «BMWman.ru»)