Spark plugs are some of the more robust parts in the engine ignition system. As their name suggests, their job is to start the spark that ignites the fuel and air mix. In cars, spark plugs can last 30000 miles, and in bikes up to 10000 miles without showing signs of visible wear. But when the time comes, the engine will begin to misfire, and you’ll hear (and feel) knocking sounds in the cylinders. Though most sparks plugs are aided by the electronic fuel injection and timing systems to work flawlessly (and prolong lifespan), eventually they’ll need to be replaced.
Choosing a new set of spark plugs can be a bit confusing, considering that there are OEM and aftermarket options. Some plugs on the market are also dubbed as ’high performance’, offering a longer lifespan due to better materials. Some bikers may also experience the need to get new spark plug wires which connect the spark plugs to the distributor. These feed the spark plugs with the required current to create the electrical arc between the electrodes and are essentially what ignites the air and fuel mixture.
Spark Plug Basics
Spark plugs provide the missing link in the combustion process – the spark that ignites the air and fuel mix to bring pistons and connecting rods down and turn the crankshaft. They do this hundreds of times each minute.
They get their charge from the vehicle battery and ignition system. This is transmitted through wires to the terminal nut and onto the centre electrode. This part is housed in a non-conductive ceramic insulator to ensure the correct flow of electricity and prevent current leakage. Past the corrugation that prevents flashover, plugs widen into a zinc plated metal shell. At the top tip of this shell is the ground electrode, and the gap between the two is where the spark or electrical arc is created. This is what ignites the air and fuel combo.
The choice of metal conductors in the electrodes is what determines the performance, lifespan and price of spark plugs. The centre electrode is commonly made of copper, while the tip electrode is either nickel in regular plugs or more exotic metals like platinum or iridium in more performance-oriented spark plugs. What needs to be consistent is the gap between the two (usually at 1mm) to ensure correct firing and timing.
When to Change Your Spark Plugs
For motorcycles, spark plugs need to be changed every 8 to 10 thousand miles, depending on the make and manufacturer recommendations. They need to be inspected at every regular service interval, roughly at 5000 miles. If there is visible discolouration (from the normal light to medium brown) in the ceramic insulation around the centre electrode, the spark plug needs replacing.
In addition, any black carbon deposits on the electrodes mean a buildup of fuel and a sure sign of misfiring. The same happens when the electrodes are eroded, with the distance between the two enlarged, hampering the creation of an electric arc.
Damaged spark plugs will negatively affect how your bike rides and the way it reacts to your right wrist. In addition, plugs past their prime will cause issues on startup, and idling. This is also dependent on the nominal heat range of the plug. A spark plug with a high degree of heat dispersal are called cold type plugs, whereas those with a low degree of heat dispersal are known as hot type spark plugs. Cold type spark plugs better handle the high temperatures, so are preferred in high output engines primed for outright speed. The two types have differently shaped and sized insulation sections, with cold type plugs having a shorter and thinner internal insulator core.
If the spark plugs are in perfect condition, and you’re still experiencing the issues above, then the problem might be with the ignition or battery, the fuel injection or timing (cams and valves), or even the fuel itself.
The Importance of Spark Plug Wires
Just as important as the spark plugs are the wires that deliver the electrical charge from the ignition coil. These will literally need to take the heat from surrounding engine parts, as well as the higher voltage ratings in newer ignition types. Wires have to be well insulated and not create electrical interference (EMI), that can interfere with the work of other electrical systems on the bike.
A good pair of wires (for twin-cylinder bikes) will have low resistance, for better current flow that also affects spark plug efficiency, and therefore performance and fuel consumption. Better built wires also emit lower levels of electromagnetic interference.