The value of the glow number shows the degree of heat load on the candle, which the candle is able to withstand. The lower the glow number of a candle, the higher its ability to withstand thermal loads. Such a candle removes heat better, preventing detonation combustion. A candle with a high degree of heat resistance has the disadvantage that it needs a high self-cleaning temperature. Therefore, such candles are covered with soot faster, especially in conditions when the engine does not reach its operating temperature during movement (traffic in the city, for short distances in winter).
The car manufacturer determines the required glow value of the candle and, accordingly, its type. There are candles with one or more electrodes, different lengths and different thread diameters. When replacing spark plugs, the vehicle manufacturer's instructions regarding spark plugs must be observed.
The average life of spark plugs varies and is due to many factors. An important role is played by the material from which the central electrode is made. Chrome-nickel alloy has high heat resistance and anti-corrosion properties. Silver conducts heat better than all metals, platinum electrodes have the highest resistance to corrosion and soot. The duration of the spark plugs, depending on the material of the electrodes and their number, can be from 30,000 km to 100,000 km.
You can independently check the gap between the electrodes of the candle.
1. Unscrew the candles and lay them in accordance with the order of operation of the cylinders. A subsequent inspection of the spark plugs will allow you to draw certain conclusions regarding the corresponding cylinder.
2. Do not apply much force if the candles cannot be unscrewed. The threads of the spark plug hole may be damaged. In this case, warm up the engine and remove the spark plugs.
Attention! Do not install cold spark plugs on a hot engine. Later they cannot be unscrewed, as in this case they will be planted as if on rivets.
3. If it is not possible to use a torque wrench when installing candles, then be guided by the following rule in order to correctly install candles.
4. Screw in the spark plug until its sealing ring rests against the surface of the cylinder head. Further tightening of the candle is impossible without the application of a certain effort. In this position, tighten the new spark plug about a quarter of a turn, and the used spark plug by turning the wrench about 15°.
Attention! In order for the candles to unscrew easily, apply a little graphite to their threads by crushing the pencil stem, or lubricate it with a thin layer of copper grease. Lubricating the threads of the candles with ordinary grease or oil only worsens the situation. Candles in this case stick to the thread of the hole.
If the thread in the hole for the candle is broken, then the workshops in this case use the corresponding threaded sleeve, which is inserted into the candle socket.
The condition and appearance of the spark plugs can tell a lot about the performance of the engine. If the candles are removed for this purpose, then the engine should first be warmed up. Inspect the spark plug, paying special attention to the center electrode insulator and ground electrodes:
- A) gray or brown central electrode insulator. The fuel injection system is well adjusted and the engine runs economically;
- b) sediment layer. The reason for this may be additives to engine oil or fuel, as well as increased oil consumption. You can change the type of oil or fuel;
- V) black sooty deposits. Due to the use of the vehicle in short-distance driving mode, the spark plugs do not warm up to the self-cleaning temperature. Incorrect glow plug number;
- G) white coating on the insulator. Too early ignition timing. Electronic ignition control or knock sensor does not work;
- d) melting of the central and side electrodes. Overheating of injectors, faulty electronic ignition control, defective knock sensor or engine overheating due to insufficient cooling;
- e) breakage of the insulator. At the initial stage, it manifests itself in the form of microscopic cracks. The result of knocking due to refueling with low-quality fuel, incorrect ignition control, defective knock sensor, insufficient cooling or lean mixture due to «suction» air;
- and) oil film on the electrodes and spark plug. Worn piston rings, valve stems or valve stem seals.
If the candle is outwardly normal, but the engine starts with difficulty, jerkily, then the reason for this may still be candles. Cracks in the ceramic insulator that are invisible during inspection of the spark plugs can be filled with fuel condensate when starting a cold engine and the spark discharge can be discharged in a different direction. The candle may not fire as a result of the pressure generated, although it produces a spark when removed.
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