Understanding Spark Plugs
All You Need To Know
What is a Spark Plug and what does it do?
All internal combustion engines require three key ingredients to run: compression, fuel and spark. Your spark plugs are a critical engine component and work to provide spark from the engine’s ignition coil(s) to ignite the air-fuel mixture inside your engine.
One of the key components of a spark plug is the high-alumina ceramic insulator which shields the electrical current from the surrounding metal on the spark plug and cylinder head. The insulation prevents current leakage and ensures electricity flows in the desired direction. From here the current forms a spark across the electrode gap, completing the circuit to the ground electrode.
For a more in-depth breakdown of all of the components of a spark plug, see the guide:
- Corrugations - Extend the insulating surface distance between the terminal and the metal shell to preventing flashover
- Powder Filling - Helps provide a gas tight seal between the insulator and metal shell
- Insulator - Provides insulation, heat resistance and thermal conductivity
- Metal Shell - Plated to provide superior resistance to high-temperature corrosion
- Copper Core - Quickly dissipates a large amount of heat for maximum performance at both high and low speeds
- Centre & Ground Electrodes - Ensures superior heat resistance and durability
- Ceramic Resistor - Prevents electrical noise from interfering with the operation of electrical parts
What Spark Plugs Do I Need?
With many seemingly confusing part numbers on the market when it comes to choosing your spark plugs, you might be wondering what are the right spark plugs for my vehicle? While spark plug part numbers may look the same, each plug has its own characteristics which are not immediately recognizable. These variations are crucial to the operation of the engine and choosing a plug that isn’t recommended for your engine can result in anything from losses in performance all the way up to serious engine damage. To determine which plugs are the best to use in your car, browse the Repco website using the REGO search function.
Once you’ve figured out which are compatible with your car, using the REGO search function on the Repco website, you need to pick which model you want to run in your engine. Whether you’re after the standard replacement, a seriously high performance, long-lasting spark plug or anything in between, NGK have an option to best suit your needs. Also note that some modern vehicles are not compatible with NGK Standard spark plugs and may require Iridium or Platinum spark plugs as standard.
Standard
- Made with nickel centre and ground electrodes
- Copper cored centre electrode to assist with heat dissipation
- Service life and longevity up to 40,000km
Iridium IX
- Iridium centre electrode for better ignition
- Copper cored centre electrode to assist with heat dissipation
- Reliable nickel ground electrode for everyday longevity
- Service life up to 60,000km
Platinum/Laser Platinum
- Performance spark plug
- Centre electrode with a fine platinum tip for increased ignitability
- Platinum-tipped ground electrode increases reliability
- Copper cored centre electrode to assist with heat dissipation
- Up to 100,000km or the vehicle manufacturers recommended service interval of service life
Laser Iridium
- The pinnacle of spark plug technology
- Combines NGK’s most high performance iridium centre electrodes with platinum tipped ground electrodes for incredible ignitability
- Copper cored centre electrode to assist with heat dissipation
- Extreme service life of up to 100,000km or the vehicle manufacturers recommended service interval, while the Iridium centre electrode outstrips the NGK platinum range in terms of spark and performance
Reading NGK Spark Plug Part Numbers
Ever wondered what the part numbers on NGK spark plugs mean? To simplify the complex letter and numbering system, below is a simple guide which you can use to decipher the part numbers used to name most nickel and single platinum or iridium spark plugs. When looking at the part number, it can be broken down into 7 simple criteria:
- Thread size and hex size
- Construction type
- Resistor
- Heat rating
- Thread reach / length
- Firing end construction
- Spark plug gap
Using the chart, and an example part number of BPR5ES-11, the specs of this spark plug have been highlighted to show that it has a thread size of 14.0mm, hex size of 20.8mm, a projected insulator type construction, resistor, heat rating of 5, 19.0mm thread reach, standard type firing end construction and a 1.1mm spark plug gap.
What Is Spark Plug Heat Range?
When it comes to spark plugs, one of the most important specs is heat rating. Heat rating is a measure of the balance of the amount of heat received from the combustion chamber and amount of heat dissipated. You need to choose a heat rating at which the spark plug can be used normally by maintaining this balance; however, this varies between all types of engines.
Hot and Cold Type Spark Plugs
Spark plugs with firing ends that heat up quickly are referred to as ‘hot type’ plugs while those which don’t heat up quickly are called ‘cold type’ plugs. When choosing spark plugs, it is essential to use a plug with a heat rating that matches your engine and the driving conditions you subject it to. If you use spark plugs with the wrong heat rating, there are some issues which can occur within your engine. With the Repco REGO search tool, you can shop a range of spark plugs with heat ranges that are safe to use with your engine.
When To Use A Hotter Spark Plug
If you are experiencing fouling issues with your spark plugs, this indicates the plug is not reaching the minimum operating temperature to burn off carbon deposits. After eliminating all other possible causes, the final step is to choose a hotter heat rating plug to increase the plugs operating temperature and reach the self-cleaning temperature. Our recommendation is to change one heat range at a time as you do not want to run a plug which operates a too high of a temperature and put your motor at risk.
All spark plug application listings made by NGK are for unmodified applications. When making modification to your engine, it is important to consider what impact each modification will have on the cylinder operating temperatures which affects the spark plugs operating temperature.
In general, any modification which increases the cylinder pressures will result in an increase in the cylinder temperatures. This can be by increasing the compression ratio or adding/increasing forced induction with a turbo or supercharger. In each of these cases, the cylinder temperature will increase, which needs to be compensated by using a colder heat range plug.
Alternatively, modifications to the induction system or fuel type which results in more fuel entering the combustion chamber has a cooling affect, reducing the cylinder temperatures.
Even differences in the tune of identical setups can result in different operating temperatures.
Therefore, it is important to understand that every modified application is unique and the individual making the modifications needs to consider the impact of all the modifications and select a suitable heat range. Our recommendation is to be conservative and start with a cold heat rating plug as this does not put your engine at risk. A spark plug which is too cold will eventually build up enough carbon deposits to cause a misfire.
If experiencing fouling issues with your spark plugs this indicates the plug is not reaching the minimum operating temperature to burn off carbon deposits. After eliminating all other possible causes, the final step is to choose a hotter heat rating plug to increase the plugs operating temperature and reach the self-cleaning temperature. Our recommendation is to change one heat range at a time as you do not want to run a plug which operates a too high of a temperature and put your motor at risk.
Why Is Spark Plug Gap Important?
An important step before installing your new spark plugs is checking and setting the electrode gap. The spark plug gap dictates the spark magnitude and when not set correctly may affect engine performance as the spark magnitude may not be strong enough to ignite the air/fuel mixture.
The electrode gap is set when a spark plug is manufactured and the plugs in the NGK range are pre-set to the correct gap for each application. Engines which have been modified to have more compression or forced induction will generally require a smaller spark plug gap to ensure correct ignition in denser air/fuel mixtures.
Due to the fine wire design of Platinum and Iridium spark plugs, the centre electrode can easily be damaged if subjected to forces it was not designed to withstand. Therefore, NGK do not recommend gap adjustment for precious metal spark plugs. However, if the gap must be adjusted, please follow the correct procedure when adjusting the gap.
How To Measure Spark Plug Gap
Gapping your spark plugs can be done with just a simple few steps and some very basic tools. When widening the spark plug gap use a tool that only pulls back on the ground electrode without touching the centre electrode or the porcelain to avoid damage. To close the gap on a plug, gently tap the electrode first on a hard surface. Repeatedly check the spark plug gap using a feeler gauge to confirm that you don’t open or close it too much.
NGK doesn't recommend adjusting the plug gap more than 0.1mm in either direction as this can damage the plug. If you adjust the plug more than this, the ground electrode and centre electrode won't align properly, which can hinder spark plug performance and reduce the longevity of your plugs.
How To Change Spark Plugs?
Now that you’ve chosen your plugs and checked the gap, you’re ready to install them in your engine. You might be left wondering how to replace a spark plug? Luckily, thanks to easy access and the need for only a few basic hand tools, replacing spark plugs is one of the easier DIY tasks for budding car enthusiasts and professional mechanics alike. Just like any time you’re working on your engine, there are a few things to consider when installing your new spark plugs.
Preparation
Before installing your new spark plugs, make sure your engine is cool. Leaving the car overnight is the best practice to make for easy, safe and comfortable plug removal the following morning. We recommend using a brush or compressed air to remove any debris from the cylinder head around the spark plugs ports to prevent dirt and grime from falling inside the engine.
Installation
One must-have tool when installing new spark plugs is a torque wrench. Most spark plug failures can be traced to incorrect torque when tightening the plugs. If left too loose, the plugs can overheat or simply loosen and even break as a result of vibrations from being too loose.
Alternatively, if you try to tighten the plugs too much, you could snap the plug off inside the cylinder head or potentially cause damage to the threads on the plug or the head which can require costly repairs. Over-tightening can also disrupt heat dissipation zones resulting in overheating or melting of the electrodes.
The best practice for installing the spark plug to the correct torque first requires you to lightly tighten the spark plug so it is finger tight – you can do this by using the socket without connecting it to the torque wrench. Once the plug is finger tight, the gasket or taper seat should just tough the cylinder head and you can then use the torque wrench to fully tighten the plug. Not sure how tight to go? See the table below for a basic break-down on spark plug torque specs.
Fig 1. Plug too loose - lacks correct thread engagement
Fig 2. – Over tightened plug, metal shell stretched and separated internal seals
If you don’t have access to a torque wrench, there is an alternative method called the ‘Angle of Rotation’
Alternative: Angle of rotation details
The respective angle of rotation can be found on the spark plug packaging. (Exception: racing plugs – only torque method)
Simply hand tighten the plug until it is seated, and then tighten further using a wrench to the angle of rotation indicated on the spark plugs packaging. In the example below, the plug Is to be tightened an additional ½ turn from being seated
Socket Sets
Spark Plugs
Oxygen Sensors
Ignition Leads
Ignition Coils
Ignition
