Contents: Normal candle 🠛 The spark plug is covered with dry…🠛 The spark plug is covered with oily…🠛 The candle is overheating 🠛
Spark plugs have a screw thread diameter of 14 mm. Use the manufacturer's recommended and specified types of spark plugs with the appropriate heat range.
The gap between the electrodes is different for each spark plug (see specifications). Spark plugs should be cleaned at least every 10,000 km. At the same time, adjust the gap between the electrodes according to the specification. When setting the gap, do not bend the central electrode, as this may crack the porcelain insulator. The location for measuring the gap is shown in Figure 4.1.
4.1 The spark plug gap is measured between the arrows
Before removing the spark plugs, make sure that no foreign bodies can get into the holes. Washers, bolts, stones, etc. that get into the spark plug hole can damage the valves, valve seats or cylinder head when the engine is first started. The appearance of the spark plug can be used to judge the suitability and flawless operation of the spark plugs, combustion, condition of the working mixture and the general condition of the engine (wear of pistons, piston rings, cylinders, oil leakage into combustion chambers, etc.).
Normal candle
The thermal cone of the central electrode insulator is covered with a dust-like coating from a weak, gray-yellow to brown color. The electrodes are visible despite the coating. The inner surface of the housing is light brown, or from yellow/gray-yellow to black-brown. With this type of spark plugs, the engine is in order. The glow number of the spark plug is selected correctly.
The spark plug is covered with dry carbon deposits
The thermal cone of the insulator, electrodes and housing are covered with a thick layer of powdery dark gray carbon. The reason for this is too rich a working mixture, a large gap between the electrodes, a high glow number of the spark plug. To eliminate the malfunction, install a spark plug with a suitable glow number.
The spark plug is covered with oily carbon deposits
The thermal cone of the insulator, electrodes and body of the spark plug are covered with black oily carbon. This may be caused by engine oil penetrating into the combustion chamber or worn cylinders and pistons.
The candle is overheating
The thermal cone of the insulator is covered with a glassy or rough coating from dark brown to dark gray, and may even be melted. The electrodes are burnt, especially the central one. The cause may be a lean mixture, poorly closing valves or a spark plug with a low heat rating, which overheats due to improperly set ignition. The deposits between the porcelain insulator of the central electrode and the spark plug body must be cleaned using a sandblasting machine. Before installing the spark plug, thoroughly clean its threads.
Since spark plugs are usually changed every 15,000 km, cleaning should be done every 10,000 km. Do not overtighten the spark plug during installation, as this may damage the sealing washer. The tightening torque should not exceed 15-20 Nm.