What does a spark plug do?
It serves as a lighter to ignite the air/fuel mixture under extreme conditions. A spark plug must dissipate the heat produced by the combustion gases.
It withstands high voltages between 20 000 V – 30 000 V.
It withstands repeated cycles between normal operating temperatures 400ºC to 800ºC and 2500ºC
It withstands chemical corrosion caused by fuel and combustion gases
It withstands pressure of 50kg/cm squared.
What do the numbers on the spark plug mean?
The numbers indicate the heat rating system. The heat rating is a measure of the amount of heat dissipation. Selecting a spark plug with the proper heat range will ensure that the tip will maintain a temperature high enough to prevent fouling yet be cool enough to prevent pre-ignition.
Hot types for low speeds
- It has a large surface exposed to the combustion gases.
- It dissipates heat slowly.
- The firing end heats up quickly.
Cold types for high speeds
- It has a smaller surface exposed to the combustion gases.
- It dissipates heat quickly
- The firing end does not heat up quickly.
Heat rating and heat flow of spark plugs
It is essential to use a spark plug that fits a specific engine and its conditions of use.
When the wrong heat rating is selected
- When the heat rating is too high:
The spark plug temperature remains too low and causes deposits to build up on the firing end; the deposits provide an electrical leakage path that gives rise to loss of sparks.
- When the heat rating is too low:
The spark plug temperature rises too high and induces abnormal combustion (pre-ignition); this leads to melting of the spark plug electrodes as well as piston seizure and erosion.
Click here to view the video on heat ratings
What does the ‘R’ stand for?
Resistor. The spark plug incorporates a ceramic resistor of 5K ohms to suppress ignition noise generated during sparking.
- It removes noises which may interfere with car radios, mobile communications and cellular phones.
- It also prevents the incorrect operation of electronic fuel injection control systems.
As the resistor spark plug has an incorporated resistor, some people think that it has adverse effects on the start-up, acceleration, fuel economy and emissions. However, this is wrong. It does not effect engine performance so don’t hesitate to use it.
Why does my spark plug leak?
It does not leak. The stain on the ceramic is caused by the oil particles suspended in the air that adhere to the surface of the insulator due to the high voltage. It does not effect the spark plug’s performance in any way.
What makes up a spark plug?
How does one fit a spark plug?
Use the specified tightening torque applicable to the spark plug.
Flat seat spark plugs with thread diameter of 18, 14, 12 and 10mm
• New plugs 1/2 – 3/4 turn (180° – 270°)
• Re-used 1/12 – 1/8 turn (30° – 45°)
Spark plugs with thread diameter of 8mm
• New plugs 1/3 turn (120°)
• Re-used 1/12 turn (30°)
3.5 – 4.0 kgm
2.5 – 3.0 kgm
1.5 – 2.0 kgm
1.0 – 1.2 kgm
0.8 – 1.0 kgm
How do you read a used spark plug?
Different manufacturers have specified service intervals for their vehicle’s spark plugs.
Examples of problems caused by excessively long periods of use: • Worn out electrodes will have difficulty in sparking.
• Deposits accumulated on the firing end may induce abnormal combustion (pre-ignition), causing problems that include melting of the electrodes
For more information about NGK, visit their website www.ngksparkplugs.co.za