Spark plug

The spark plug consists of an insulator, a housing, a center electrode and a ground electrode. The central electrode is hermetically fixed in the insulator, and the insulator is firmly connected to the housing. An electric spark jumps between the electrodes, which should ignite the air-fuel mixture. Starting qualities of the engine, idling properties, acceleration and maximum speed of the car depend on the spark plug. Therefore, it is impossible to deviate without reason from the type of candle prescribed by the factory, which is determined by the glow number. The heat number indicates the degree of permissible thermal load of the spark plug under certain operating conditions. Spark plugs for the engines have been chosen to achieve their self-cleaning temperature as far as possible under all road conditions. The lower the glow number of a spark plug, the higher its resistance to glow ignition and the less its resistance to fouling. The higher the glow number of a spark plug, the lower its resistance to glow ignition and the higher its resistance to fouling.

The heat number is contained in the designation of the candle. This designation includes the following:

Example: Bosch spark plugs



1 - thread

• W - thread M14 x 1.25 with flat seal, SW 21; (SW - turnkey size)
• F - thread M14 x 1.25 with flat seal, SW 16;
• M - thread M16 x 1.5 with flat seal, SW 25;
• H - thread M14 x 1.25 with conical seal, SW 16;

2 - Heat number. The thermal scale value is indicated from DB "cold") up to 13 ("warm"). In this case, the number V corresponds to a thermal value of 150 (former designation), 7 - 175.6 - 200, etc.

3 - thread length.

• B - thread length 12.7 mm, elongated trajectory of the spark discharge;
• C - thread length 19 mm, normal trajectory of the spark discharge;
• D - thread length 19 mm, elongated spark discharge trajectory;
• L - thread length 19 mm, far elongated spark discharge trajectory. The thread length data refers to spark plugs with a flat seal. Additional character T (e.g. D.T) indicates the presence of three mass electrodes.

4 - Execution of electrodes.

5 - Material of the central electrode:

• in the absence of a symbol - Cr-Ni - alloy;
• C - Ni-Cu - alloy;
• S - silver;
• R - platinum.

6, R - with resistance to protect against interference. Thanks to this, the operation of the ignition system is not disturbed.