The gap between the electrodes is different for each candle (see specifications). Spark plugs must be cleaned at least every 10,000 km. At the same time, adjust the gap between the electrodes in accordance with the specification data. When setting the gap, do not bend the center electrode, as this may crack the porcelain insulator. The gap measurement point is shown in illustration 4.1.
4.1 The spark plug gap is measured between the arrows
Before turning out the spark plugs, make sure that no foreign bodies can get into the holes. Washers, bolts, stones, etc. caught in the spark plug hole. may damage the valves, valve seats or cylinder head when the engine is first started. By the appearance of the spark plug, one can judge the suitability and flawless operation of the spark plugs, combustion, the state of the working mixture and the general condition of the engine (wear of pistons, piston rings, cylinders, oil inflow into combustion chambers, etc.).
Normal candle
The thermal cone of the insulator of the central electrode is covered with a dusty coating from a weak, gray-yellow to brown color. The electrodes are visible despite the plaque. The inner surface of the body is light brown, or from yellow / gray-yellow to black-brown. With this kind of candles, the engine is in order. The heat value of the candle is chosen correctly.
The candle is covered with dry soot
The thermal cone of the insulator, the electrodes and the body are covered with a thick layer of powdery dark gray soot. The reason for this is too rich a working mixture, a large gap between the electrodes, a high glow number of the candle. To eliminate the problem, install a candle with a suitable glow number.
The candle is covered with oily soot
The thermal cone of the insulator, the electrodes and the body of the candle are covered with black oily soot. The reason for this may be the penetration of engine oil into the combustion chamber or worn cylinders and pistons.
The candle is overheating
The thermal cone of the insulator is covered with a vitrified or rough coating from dark brown to dark gray, and may even be melted. The electrodes were burned, especially the central one. The cause may be a lean mixture, poorly closing valves, or a low glow plug that overheats due to an incorrectly set ignition. Deposits between the porcelain insulator of the center electrode and the body of the candle must be cleaned with a sandblaster. Thoroughly clean the threads of the spark plug before installing.
Since the spark plugs are usually changed every 15,000 km, cleaning is necessary every 10,000 km. Do not overtighten the spark plug during installation as the sealing washer may be damaged. The tightening torque must not exceed 15-20 Nm.