When removing candles, all of the above safety measures should also be observed. First of all, disconnect the battery. Spark plugs must be replaced within the time specified in the service plan.
When removing the candles, make sure that foreign objects do not get into the holes into which the candles are screwed. Failure to comply with this requirement leads to the fact that after installing the candles and starting the engine, the valves, valve seats or even the cylinder head are damaged.
By the appearance of the candle, certain conclusions can be drawn about its functioning, mixture formation and the state of the engine (pistons, piston rings, etc.).
The candle is normal if there is a slight powdery coating from a gray-yellow to a gray-brown hue on the electrodes and insulator. At the same time, this indicates that the engine is also in order. The heat value of the candle is also chosen correctly and corresponds to the operational loads.
If the spark plug body, insulator and electrodes are covered with a thick layer of powdered soot (soot) black-gray, this means that the mixture formation is not adjusted correctly and the air-fuel mixture is oversaturated. The air supply is too low, the air damper is activated too long, the gap between the electrodes is too large, the glow number of the plug is too high and its temperature when the engine is running is below the required operating temperature.
The presence of oily soot on the insulator, electrodes and body of the candle indicates that engine oil enters the combustion chambers. The reason for this may be worn pistons or piston rings.
The presence on the insulator of glassy, sticky deposits of a dark brown or even gray-black color, which sometimes have the form of drops, with simultaneous damage to the electrodes, especially the central one, and the candle body is evidence of a lean mixture, a loose candle, poorly closing valves. The reason for this may be the candle itself, because its glow number does not match the needs of the engine.
If the car is filled with leaded gasoline, then the insulator of a normally working spark plug has a gray tint. Deposits that accumulate between the insulator and the center electrode are recommended to be removed with a jet of sand from the spark plug tester. Before installing candles, be sure to clean their threads.