A spark plug with a high heat rating (a "hot" plug) will become very hot, causing pre-ignition. A spark plug with a low heat rating (a "cold" plug) may not reach the required self-cleaning temperature, causing the insulator's thermal cone to become dirty.
The gap between the electrodes and the length of the threaded part. In addition to the required heat range for the respective engine, the spark plugs must also have a certain gap between the two electrodes.
When replacing spark plugs, observe the following precautions:
- when removing spark plug tips, pull not by the cable, but by the tip itself;
- when unscrewing the spark plugs, stack them in the order of the cylinders. The appearance of the spark plugs can be used to determine the failed cylinder;
- cold spark plugs often sit very tightly. In this case, remove the spark plugs on a hot engine;
- screw in new spark plugs on a cold engine;
- tighten the spark plugs to 15 Nm. If you do not have a torque wrench, loosely screw in the spark plugs with a spark plug wrench until the sealing ring is seated. If you are installing new spark plugs, tighten them with a spark plug wrench by a quarter of a turn. If you are installing old spark plugs, tighten them by 15°.
The appearance of the spark plugs can be used to judge the condition of the engine.
Normal candle. The insulator is covered with a slight gray-yellow (to brown) coating. On the electrodes there are gray-yellow (to brown) deposits. The inner part of the housing has a light-brown or yellowish (to black-brown) coating.
Smoked candle. The thermal cone of the insulator, the electrodes and the inside of the housing are covered in most cases with a thick black-gray velvety coating.
Reasons:
- very rich working mixture;
- lack of air;
- too big gap between electrodes;
- very high heat rating (the spark plug is too "cold").
The candle is oiled. The thermal cone of the insulator, the electrodes and the body of the spark plug are covered with greasy, oily-shine soot. Formation of oil carbon deposits.
The reason is engine oil getting into the combustion chamber (wear of the cylinder-piston group, failure of the oil scraper caps).
Overheating of the spark plug. The thermal cone of the insulator is covered with a dark brown (to gray-black) glaze. In most cases, deposits are observed at the end of the thermal cone of the insulator. Causes:
- lean mixture;
- a loosely wrapped candle;
- valves that do not close well;
- spark plug with too low heat rating (spark plug is too "hot").
When using fuel with lead additive, the thermal cone of the insulator will have a gray burn under normal conditions.
The deposits between the porcelain insulator of the central electrode and the spark plug body are cleaned with a sand jet from a spark plug tester. When screwing in the spark plugs, clean the threads.
This publication was borrowed from the website (FORDBOOK.ru)