Guide to Motorcycle Spark Plugs – All the Basics

A motorcycle cannot run if there are no igniting sparks from the plugs. They are small but play a critical role in running a motorbike smoothly. But plugs lose their work capacity over time due to use, so you’ll be required to replace these at regular intervals. Replacing worn spark plugs with newer ones can improve your bike engine’s performance impressively. They are inexpensive, and you can replace yourself at home with some basic tools.

Working Science of Spark Plug

A motorcycle engine (read all automotive engines) is an incredible machine designed to convert energy (octane or petrol) into movement. What’s the science behind it? “Internal Combustion” – credit goes to this scientific principle. To convert a potential source of energy (fuel) of your motorcycle into a source of kinetic energy, which gives an object a motion, the engine requires a path to release. The path of such release is known as the combustion process.

The process is caused by the engine cycle. The engine’s valves fill the cylinder with an air-fuel mixture in the cycle, a highly explosive compound for combustion. When the piston moves upward inside the engine when cycling, the mixture gets compressed in a very tiny space, generating more energy. The spark plugs come into functioning at the point when the compression reaches its peak. They create tiny sparks that ignite the mixture, which immediately creates an explosion that pushes the piston to move downward. The engine crankshaft gets turned and produces kinetic power that makes your motorcycle run forward.

We practically see an arc of current across two leads of spark-plugs, set with a gap in between and are not connected physically. But they are close enough so that the produced electricity can jump the gap timely and accurately. Generally, we call spark plugs the ignitor, and they are the most critical component of the whole ignition system (plug wires, power source, etc.) despite being so small and inexpensive.

Structure of Spark Plug

Motorcycle spark plugs are made from very durable material. Although small, it is robust and enduring. We already know that its function is to cause explosions, so it is casual for a spark plug to hold out against the resulting current and heat. As a result, it’s structurally capable of withstanding millions of explosions till the lifespan. However, the efficiency will decrease at some point after use, so the engine’s performance also decreases. After a certain period, misfire or complete failure to fire occurs, and that’s the point before which you should replace spark plugs.

Signs of a Bad Spark Plug

Although a spark plug has a potential lifetime, as we said in the next paragraph, it often fails to accurately determine when to replace it due to variations in motorcycle use and mileage. However, there are some signs from which you can assume that the functionality of the plug is almost over. Foremost among those are as follows:

  • Rough and jittery sound when the engine runs at idle.
  • Trouble at sparkling and eventually starting.
  • Engine misfires occurring due to incorrect firing from cylinders.
  • The engine begins surging by sucking more air required for combustion.
  • Finally, the motorcycle becomes unresponsive, and the accelerator loses sensitivity.

Motorcycle Spark Plug Replacement – Time and Compatibility

Replacing spark plugs at the right time assures you of peak performance by your motorcycle. The question is, when to replace them or how often they should be replaced?

Motorcycles have reached their current position after a long journey. Modern motorcycles are much more cost-effective in terms of structure, technology, and transcendence, and spark plug replacement is no exception.

However, nearly for all motorcycles (including the 4-cylinder engine Harley), spark plugs should be replaced once every 24,000 to 26,000 kilometers. But for certain or uncertain reasons, the bike may run rough, sputter, or lose power earlier. If you see things happening like these, you should check if it’s time to replace the spark plugs.

If it’s a second-hand motorcycle, the buyer should ask the previous owner when he last changed the spark plugs and how many kilometers (approximate) they have run since then. If the seller fails to give any information, you may run for a while and try to observe if it shows any sign of a bad spark plug, as we explained above. But if you feel insecure, it’s better to replace immediately after a second-hand purchase without waiting for a sign.

However, compatibility is a critical factor when replacing spark plugs. Therefore, you should check and make sure that you’re buying the most compatible plugs for your motorbike, in terms of both – the bike model and the engine type.

How to Replace a Motorcycle Spark Plugs

When you find the right one, just follow the simple steps and make a perfect DIY replacement:

1. Cool the engine

2. Remove the spark plug wires

3. Clean the spark plugs

4. Remove the spark plugs

5. Check and clean the cylinder heads

6. Place the new spark plugs and check the fitting

7. Use hand for primary screw, then screw and tighten with spark plug wrench

Concluding Remarks

Improving the engine performance of a motorcycle must need efficient spark plugs. The small part of a motorbike has a remarkable working role. They come with an approximate lifespan – they give signals when worn or incapacitated – and you can easily replace these without professional assistance.


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