Pull out all spark plug plugs, pulling only by the plugs, not by the wires. You can use special pliers for pulling out (eg HAZET 1849). In this case, the plug should be held only by the metal sleeve.
If possible, blow out the spark plug niches with compressed air.
Remove the spark plugs with a special spark plug wrench and check the appearance of the spark plugs. Based on experience, you can draw conclusions about the operating conditions of the engine.
The following rules apply. Electrodes and insulator:
- Medium gray - correct carburetor adjustment and correct spark plug operation.
- Black - enriched mixture.
- Light gray - lean mixture.
- Oily - interruptions in the operation of the corresponding spark plug or poor sealing of the piston rings.
Clean the spark plugs with a brass brush or sandblaster.
Check the spark plug insulators for leakage currents. Currents appear as thin, irregular traces on the outer surface. If it is not possible to completely remove traces of leakage currents, replace the corresponding spark plug.
If necessary, file down the middle electrode with a rectangular file and remove the carbon deposits.
Check the distance between the electrodes using a flat feeler gauge. The reference value is 0.8 mm.
To set the distance between the contacts, bend the ground electrode. There is a simple, practical tool for this, otherwise tap the side of the ground electrode. When bending, rest a small screwdriver on the edge of the spark plug thread. Never on the central electrode, otherwise it may be damaged.
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.
Attention: Do not install the spark plugs at an angle.
Tighten the spark plugs to 20 Nm.
Note: If a torque wrench is not available, turn new spark plugs with a flat sealing ring (R) further by 90° (1/4 turn). Spark plugs with a conical sealing ring (B) should be turned at an angle of 15°, in the same way as used spark plugs with a flat sealing ring.
If the spark plugs are tightened too tightly, the threads in the cylinder head can be torn or damaged when unscrewing them. In this case, the threads can be repaired using special repair kits.
Place the tips on the spark plugs.
Check the strength of their fit and the wires by rocking them back and forth.