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Many riders know that the gap between the two electrodes of a spark plug is the most crucial element of the plugs. This gap determines the amount of work required by the ignition components to create a spark and ignite the system. Therefore, the larger the gap, the more work must be done to accomplish the ignition. Also, while the original gap is necessary to get right, it is also essential to understand that the gap increases over time due to regular use, meaning that the longer a spark plug is in, the more work your ignition system has to do to achieve startup, and the more wear and tear the electrodes go through. Thus, in answer to that age-old question, why gap matters, the gap matters because it determines the effort required to initiate the spark that ignites the engine.

Now, as to how to properly gap a plug, you should use a tool, like a coin gap tool, to ensure that you get a precise gap. However, those $2.00 finds are not always the best or most appropriate choice for every type of spark plug. While copper-core spark plugs take to this type of tool just fine, some of the more modern motorcycles have started using precious metals for spark plug construction, and the traditional coin-style tool can damage these metals or scrap it off the electrodes, damaging the plug. Additionally, some of these newer spark plugs use more delicate wires which can also be damaged with the old coin-style tools. Therefore, to save yourself a lot of frustration and money, it is crucial to understand how to gap both styles of spark plugs and what tools to use in either situation.

The Pre-Gapped Myth

Before moving on to the how-to guide, it is necessary to address the myth of the pre-gapped spark plug. While it is true that many plugs will stipulate that they are pre-gapped, you should take that printed statement with a grain of salt. Spark plugs are used in a wide array of engines from stationary motors, medium-duty trucks to snowmobiles and motorcycles, meaning that the gap required in all those engines is bound to be at least slightly different. Therefore, to ensure the optimum performance of your engine and the least amount of wear on your ignition, you should, at a bare minimum, check the gap with a spark plug gap adjustment tool to be on the safe side.

Gapping a Copper Core Spark Plug with a Gap Tool

The first lesson in how to gap a spark plug is to understand the proper way to use a coin-style gap tool, or the SG-2 from Ullman Devices. While it is tempting to use this tool regardless of your type of plugs, it is best used only on copper-core plugs and not on the newer devices that use precious metals, like platinum and iridium.

Now, the first thing you want to do is make sure that you know the appropriate gap for your bike. If you don’t, you can look in your manual or check your emissions sticker. The sticker should be located on the swingarm, frame or under the seat. Once you have this information, you can use the tool to find and adjust the gap, but do it in the right way.

Insert tool between electrodes and rotate

On the outer edge of the gap tool, you will notice a ramp with measurements. Insert the ramp between the electrodes and slowly rotate the device until you feel resistance. Now, you can look at where the gauge is stopped to read the measurement of the gap before moving on to the next step.

If too wide, tap on surface to close gap

If the gap gauge is giving a measurement that is wider than the recommended gap for your bike, then you need to reduce the gap. Thankfully, reducing the gap is easy. Take your plug and tap it against a surface to close the gap to the desired measurement. However, do it gently so that you do not damage the alumina insulator or porcelain.

If too narrow, don’t use the ramp

While tempting, and many people do incorrectly use the gap gauge in this way, you should never use the ramp to open or widen a gap that is too narrow. It seems counterintuitive, but the ramp is only meant for measurement. Using the ramp in this way can damage the tool as well as the spark plug, so whatever you do, do not use the ramp. Use the gapper.

Use the hole and the gapper

When looking at the gap tool, that convenient little hole that most people use to secure the tool to their keychain actually serves another designated purpose. That hole contains the gapper device. Therefore, if the gap is too narrow, put the ground electrode through the hole, and use the inside ridge, the gapper, to pry the gap open to the desired width. However, do this gently because a little pressure goes a long way.

Using a Better Tool

For newer spark plugs, those using precious metals, you should try and find a wire-type gap gauge or a feeler gauge because these tools are better for handling more delicate materials in a more precise way. While coin-style tools are handy and likely fine for copper-core adjustments, these tools are abrasive and potentially inaccurate when used with modern spark plugs. Therefore, it is vital to use a device that is made for your type of plugs. Wire tools and feeler tools also help you determine the width, but they provide a more linear surface, which allows you to check both the thickness and squareness of the gap. Also, when adjusting, these tools often have an electrode bender which works similarly to the gapper on the coin-style tool.

While it may be tempting to learn how to gap spark plugs without tool, the sensitive and precise nature of these devices means that you should always use a tool, and honestly, you should probably have multiple tools for making finer adjustments to an array of plugs. Therefore, find a proper spark plug gauge and spark plug gap adjustment tool before modifying your plugs.



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