Spark plug

The spark plug consists of a middle electrode, an insulator and a ground electrode. An ignition spark jumps between the middle and side electrodes, which ignites the fuel-air mixture. Starting reliability, idling parameters, engine acceleration and maximum vehicle speed depend on spark plugs. Therefore, it is not recommended to unnecessarily change the type of candles prescribed by the manufacturer, which is determined by the glow number and other characteristics.

The glow number shows the degree of maximum allowable thermal load of the spark plug in the engine under certain operating conditions. Spark plugs for each specific engine are selected so that they reach the self-cleaning temperature as far as possible in any mode of engine operation. The lower the glow number of a spark plug, the higher its resistance to glow ignition and the less resistance to fouling. The higher the glow number of a spark plug, the lower its resistance to glow ignition and the greater its resistance to contamination.

The glow number is indicated in the marking of the spark plugs. The marking is deciphered as follows:

Candles from Bosch:

Example	W	R	7	D	WITH
	1	2	3	4	5

1. W - M14x1.25 thread with a flat turnkey fit of 21 mm; F - M14x1.25 thread with a flat turnkey fit of 16 mm; M - thread M18x1.5 turnkey 25 mm; H - M14x1.25 thread with a conical turnkey fit of 16 mm; D - M18x1.5 thread with a 21 mm conical fit.

2. R - with additional resistance.

3. Heat number. The values of the glow number range from 06 ("cold") up to 13 ("hot"). In this case, the heat number 7 corresponds to the heat number 175 (old designation), 6 - 200, 5 - 225, etc.


4. A - thread length 12.7 mm, spark of normal length; B - thread length 12.7 mm, elongated spark; C - thread length 19.0 mm, spark of normal length; D - thread length 19.0 mm, elongated spark.

5. Material of the middle electrode. Cr-Ni - chromium-nickel alloy, C - copper-nickel alloy, S - silver, P - platinum, O - standard spark plug with reinforced center electrode.

In the presence of copper (Cu), and even more so of the silver rod of the central electrode, the thermal conductivity of the candle, and hence the maximum thermal load, increase.

Beru candles:

Example	18	TO	7	IN	U
	1	2	3	4	5

1. Thread diameter in mm (here - M18).

2. Design feature. K - tapered fit, R - with resistance to protect against interference.

3. Heat number (like candles from Bosch).

4. Thread length (like candles from Bosch).

5. Middle electrode material (U - cupro-nickel alloy). Spark plugs with a silver center electrode are designated "RS" (e.g. RS35).

It is possible to install candles with a glow number different from that recommended by the manufacturer if the operating conditions are significantly different from normal and because of this, engine malfunctions occur. If the candles are constantly covered with soot, then they do not reach the self-cleaning temperature, and they need to be replaced with candles with the next highest value of the glow number. If the engine is not producing full power, lower glow rating plugs may be required.