The main characteristic of a candle is the glow number. The heat number determines the coefficient of heat resistance of a spark plug in an engine under certain operating conditions. The spark plugs are selected in such a way that they can reach the self-cleaning temperature in all operating modes.
The lower the glow number of the plug, the higher its resistance to glow ignition and the lower its resistance to contamination. The higher the glow number of a spark plug, the lower its resistance to glow ignition and the higher its resistance to fouling.
The glow number is included in the spark plug code. The code is decoded like this:
BOSCH spark plug
Example: | W | R | 7 | D | WITH |
1 | 2 | 3 | 4 | 5 |
- 1 W - M14x1.25 thread with flat fit,
- M - M18x1.5 thread with a flat fit,
- H - thread M14x1.25 with a cone fit,
- D - thread M18x1.5 with a cone fit, key 21 mm or H / F - 16 mm.
2 R - with noise suppression resistor. The interference suppression resistor does not affect the function of the ignition system.
3 - Heat number of the spark plug. The school of meanings is divided into divisions from 06 ("cold") up to 13 ("hot"). The number 7 corresponds to the old glow number 175 (older designation), 6 - 200, 5 - 225, etc.
4 A - thread length 12.7 mm, normal suit; B - thread length 12.7 mm, offset spark, C - thread length 19 mm, normal spark, D - thread length 19 mm, offset spark.
5 - The material from which the middle electrode is made: chrome-nickel-alloy, C - nickel-copper, S - silver, P - platinum, O - standard spark plug with hardened middle electrode.
Beru spark plugs
Example: | 14 | R | 7 | IN | U |
1 | 2 | 3 | 4 | 5 |
1 - Thread diameter in mm, here M14
2 - design features, for example, R interference suppression resistor.
3 - heat number (like Bosch).
4 - thread length (like Bosch).
5 - electrode material, for example U - copper core. A spark plug with a silver-plated center electrode has the designation RS, e.g. RS 35.
Thermal resistance is increased by using a copper core (Cu) in the middle electrode and even more due to the silver-plated middle electrode. The advantage of spark plugs with a platinum center electrode is a high ignition readiness, as well as low wear and a larger range of glow numbers.
OPEL spark plugs
801 - thread length 12.7 mm, with interference suppression resistor.
802 - thread length 19 mm, with interference suppression resistor.
It is possible to deviate from the heat numbers recommended by the plant only when the working conditions differ significantly from normal conditions and there are interruptions in work.
If the candles are sooty, then they do not reach the self-cleaning temperature (only but short sections of traffic), it is recommended to replace them with spark plugs with a higher glow number. Finally, if the engine is to be run at full throttle, a lower glow rating can be used.
To make it easier to start the engine at low outside temperatures, you can temporarily reduce the distance between the electrodes from 0.7 mm to 0.5 mm.
Appearance of the screwed part of the candle
If you have some experience in the appearance of the candle, you can draw a conclusion about the condition of the engine.
Electrodes and insulators:
- gray - correctly adjusted carburetor and proper operation of spark plugs
- black - too rich mixture
- light gray - mixture too lean
- oily - interruptions in the operation of the corresponding spark plug, worn or stuck piston rings. Spark plugs can be cleaned with a brush or sandblast.
Platinum spark plugs have reached their wear limit when the middle electrode becomes invisible in the insulator. In this case, replace the spark plugs.
Every 15,000 km, the spark plugs should be unscrewed and the appearance of their screwed-in part, the distance between the electrodes, as well as wear due to burning, should be checked. Replace spark plugs if necessary.
Tighten all spark plugs to 20 Nm.
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