Show Your Spark Plugs Some Love

Show Your Spark Plugs Some Love

For many riders, spark plugs are just those things that you screw into the cylinder head and forget about.  While I’m sure that we’re all guilty of this, there are a few easy things that we can do to not only make our machine run better, but also keep it running longer.  It’s the little things that can add up over time and create the big problems, so follow these tips and give your spark plugs the love and attention they deserve.

 Spark Plug

Installing the Spark Plug

So let’s start with the basics here.  We have all been in a time pinch and simply done the hand tighten and give it a quick crank with spark plug wrench.  While a lot of the time this won’t have major consequences, there are times that this could lead to some serious damage if you’re not careful.  When a spark plug is properly torqued in, it helps to remove heat from the combustion chamber.

A loose or under-torqued spark plug will slow the heat being removed from the combustion chamber.  This happens because the spark plug is not in direct contact with the seat in the cylinder head.  The heat then has to travel farther and there is less transfer of heat through conduction.  This can cause the combustion chamber’s temperature to rise to dangerous levels.  When this happens, pre-ignition and detonation can occur.  Pre-ignition is when the temperature of the combustion chamber is so high that the air-fuel mixture will ignite before the spark plug sparks.  This can lead to the engine still firing in carbureted machines even if it is switched off.  Pre-ignition and detonating can eventually lead to engine failure because the timing will be off in the other cylinders.

If you’re thinking that all you have to do to prevent that is to tighten the crap out of the spark plug, you should think again.  If you torque the spark plug too hard, it can stress the shell of the plug, which can cause two things.  The first is that it can change shape of the inner gas seals and the second is that over-torqueing can cause a fracture in the plug’s insulator.  When either of those two things happen, the heat transfer of the plug can be slowed, which is what you were trying to avoid in the first place.

So what is the right way to install a spark plug?  You need to treat it with some love and care.  If you have a torque wrench, you can follow the specific specs for that brands plug in your machine and remember that specs for an NGK plug might be different from an Autolite.  If you do not have a torque wrench or do not carry one with you while riding, you can follow these steps to ensure that you get the proper torque.  You will want to finger-tighten the plug until the gasket reaches the cylinder head.  Once you have reached that point, use your spark plug wrench and tighten the plug about ½ to 2/3 of a turn more.  If the seat is tapered, only give it about  1/16 of a turn.


  1. Clean all of the dirt and debris from the threads before installing.  Dirt and Debris can cause the plug to be under-torqued.
  2. Do not install the plug when the engine is hot.  The metal expands and getting the proper torque can be difficult.  If you absolutely have to change the plug right away on a ride, be sure to re-check the torque when you are done riding.


Spark Plug Gapping

Gapping toolHaving the right gap in your plug can determine how efficient your machine is going to run.  Most of the time, a new plug will be gapped fairly close for its specific fitment, but it is always a good idea to double check it.  The size of the spark plug gap affects the tip temperature of the plug and the voltage that it produces.  Without the proper temp and voltage, the air/fuel mixture will not ignite as well as it should.  To properly gap the plug, a flat feeler gauge or a wire gauge gapping tool like the one that Motion Pro produces will work best.  Follow these steps to get the correct spark plug gap.

  1. Find the correct gap size for your machine.  This is usually listed on the emissions tag on your machine or the owner’s manual.
  2. Place the correct size wire from the gapping tool into the spark plug gap.
  3. If you need to adjust the gap, use the back of the tool to open or close the gap to the desired size.  Using the older coin style gapping tool or a different tool altogether can damage the spark plug tip, so be careful.

If you have a modified engine, your gap size will most likely need to change.  So if your engine has higher than normal compression or you have added a turbo or supercharger, the gap will need to change.  When your engine makes more power than stock, the spark plug gap can be smaller.  If you want to a larger gap for better fuel burning efficiency, you can open up the gap, but if you do that, you will need to upgrade to a high power ignition system to keep the correct voltage.


Spark Plug Cleaning

Not all under-performing spark plugs are junk.  Some of them can be cleaned up to perform for you once again.  Carbon can build up on the bottom of the plug, which does not allow it to spark as well as it should or not at all.  The easiest way to get rid of this is to take a wire brush and scrape away the carbon.  If it is being persistent, you can spray some carb cleaner on it to help loosen the carbon deposits and then use the wire brush.  Some people recommend burning the carbon off or using a light sand blast to remove it.  These two tactics are not ideal because if it is not done carefully, it could end up damaging the plug.  Also, if the plugs are cheap enough, you have to consider if these tactics are worth your effort.

After you are done cleaning the plug, you should check the gap size to make sure it was not altered.  Cleaning the plug is not always the cure, though.  All spark plugs will eventually wear out and need to be replaced at some point in time.


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