- Candle wrench, available in the on-board tool kit or commercially available.
- Additionally, it is recommended to purchase special pliers, such as HAZET 1849, which facilitate the removal of candle tips.
The following wear parts must be purchased:
- Spark plugs of the recommended type.
Spark plugs should be replaced every 20,000 km. Platinum spark plugs tend to last longer. They should be replaced when the center electrode is no longer visible in the leg of the insulator.
Withdrawal
May 1990 520i/525i models only. (four-valve engines)
Remove the oil filler cap.
Remove the plugs from the mounting bolts, unscrew the two bolts located under the plugs. Remove the cylinder head trim.
Remove the connectors from all ignition coils, to do this, remove the connector brackets.
Loosen the bolts securing all ignition coils, pull out the ignition coils.
Attention: There are ground jumpers on the ignition coils of the 3rd and 6th cylinders. When installing, they should be screwed to the same places.
Remove all ferrules, while pulling not on the wire, but on the ferrule. Said pliers facilitate removal.
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.
Remove all spark plugs using the special spark plug wrench.
Inspect spark plugs. With some experience, the appearance of the candle can determine how the engine works.
Table 1
Check spark plug insulators for leakage currents. Leakage currents leave thin, uneven traces 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 motors except four-valve: Check electrode spacing with feeler gauges. Set value: 0.7-0.8 mm. On new candles, the interelectrode distance is usually set correctly.
If it is necessary to bend the center electrode at a right angle to compensate for burning.
To adjust the distance between the electrodes, bend the ground electrode. To do this, there is a simple, practical tool, in the absence of which you can lightly strike the electrode from the side. When bending, rest a small screwdriver against the edge of the thread of the candle, but not against 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 as far as they will go.
Attention: Do not skew candles.
Tighten the spark plugs to 25 Nm.
Attention: If a torque wrench is not available, it is necessary to tighten the spark plug with a flat seat A with a spark plug wrench by about 90° (¼ turn. Spark plugs with tapered seat B must be turned back by approx. 15°in the same way as used spark plugs with a flat seat. Spark plugs that are too tight may break off when they are removed or the threads in the cylinder head may be damaged. In this case, the spark plug holes need to be repaired with UTC or Heli-Coli inserts.
Connect spark plugs according to ignition sequence 1-5-3-6-2-4.
Check by shaking the reliability of fastening of candle tips.
Four-valve engines: Install ignition coils and shrouds. Installation is carried out in the reverse order. Check the reliability of the fastening of the connectors and ground jumpers.