As the source for spark plugs, we pride ourselves in the technical spark plug information contained on our website. We enjoy providing that technical information on the forums, so here are some of the common topics and questions in regards to spark plugs. If you have any additional questions, please feel free to ask!

Subject covered by this post:

Basic Spark Plug Construction
How do I cross reference from one brand to another?
What are resistor plugs?
What are V-cut or U-grooved plugs?
Multi-Ground Plugs
What are Fine Wire Plugs?
What Is Platinum?
What Is Iridium?
How long will my iridium plugs last?



Basic Spark Plug Construction


Let's start out with the basic construction of a spark plug.


Starting at the top, the TERMINAL can come 3 ways:
stud - some wires are made to fit over plugs that don't have a terminal nut on top, the plug is produced with the terminal nut left off.
solid - the terminal nut is permanent and can not be removed. Used particularly in the motorsport and marine industry when there is a lot of movement and vibration and a removable terminal nut could come loose.
removable - the plug comes with a terminal nut, but it can be removed.


HEX - This is the area your socket grabs when removing or installing plug. For automotive applications, plugs usually come with a 5/8 or 13/16 hex. Vehicles prior to about 1980 allow for a 13/16 hex, most after 1980 only allow 5/8.


SEAT - Plugs are available in a tapered seat or with a gasket. The two are not interchangable - in order to use a plug with a tapered seat, your cylinder heads must have been made specifically for the use of a plug with a tapered seat.


REACH - The plug reach is measured from the seat to the end of the threaded are (do not include ground strap in measurement).


THREAD DIAMETER - Accurate Measurement of the cylinder head or removed plug is necessary to determine the plug diameter, which may range form 8mm to 18mm.


GROUND ELECTRODE - Ground electrodes come in a variety of shapes and sizes. They are also called by a variety of names depending on manufacturer, IE: trapezoid cut ground, tapered cut ground, fine wire ground, angled ground, trimmed side electrode, wedge shaped ground, inverted V-tip ground, cut back ground, etc. All have the same purpose, to reduce quenching and shadowing. Ground straps will be discussed in more detail in future technical threads.


CENTER ELECTRODE - A traditional center electrode is 2.5mm. Manufacturers have improved spark plug performance by creating fine-wire, taper cut, necked down and v-power center electrodes. Each of these will be discussed in further detail in future technical threads.


GAP - A spark plugs’ tip temperature and the voltage necessary to fire the plug are directly affected by the gap setting. Most manufacturers set the gap from the factory for that plugs most popular application. Unfortunately, that plug may have hundreds of applications from automobiles to golf carts. Setting the gap for your particular engine is important as insufficient spark plug gap can cause pre-ignition, detonation and even engine damage. Whereas too much gap can result in a higher rate of misfires, loss of power, plug fouling and poor fuel economy. Even if the preset gap is supposed to match your motor, it is always best to physically check that the gap is adjusted properly for your motor prior to installation as the gap may have been changed during shipping.






How do I cross reference from one brand to another?

From the SparkPlugs.com home page, type the part number you wish to cross-reference from into the "PART NUMBER/CROSS-REFERENCE" box located in the center of the page.
DO NOT include the manufacturers name in the part #, In other words if you are crossing over an AC MR43T, you would put in MR43T, NOT ACMR43T.

 

Thanks for the spark plug info. I wondered about the Iridium plugs - guess nex time I need to replace the regular ones on the Sporty I'll elect to go with the NGK Iridiums. Thanks again for a comprehensive review of the different types available.

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How come I can't look up my spark plugs by application (motorcycle) on your website?

 

The first lookup box is vehicle type - choose powersport, then the brand of sparkplugs you're looking for, then it will allow you to specify your motorcycle data.

 

Thank you very much unfortunately it doesn't cover the new 2003-up buells. I'm just looking for an alternative to the dealerships SE brand.

 

Sorry about that - it usally takes the plug manufacturers a couple of years to release new recommendations. We have ways of getting around it though If you want to send me your exact make and model I can check one other source for information we haven't recieved yet. Our second alternative is to use the dealer part number to cross reference over to ngk.

 

Great info! I'm running the NGK iriduims now and I'm having issues with the front cylinder plug. I checked it today and it was oil fouled. There was alsoa bit of oil around the base of the plug. I guess I'm getting too much oil in the front cylinder and its burning oil. The air filter was good though. Any ideas? Maybe a seal in the cylinder? Thanks!

E.

 

What is the best plug fore the 03 fatboy?

 

Hey man, I'm sorry - I replied to your post a couple days ago, but I guess it didn't go through.

Here are a few possible causes of wet-fouled plugs - worn rings/pistons, excessive cylinder wear, and a leak in the oil combustion chamber. Hope this helps with your trouble shooting process.

 

I'm not seeing the fatboy on any of the manufacturers data - is it sometimes called by something else?