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Notes From The Road

The Lightning Bolt Inside Your Engine
By Wayne Scraba/autoMedia.com

Spark Plug Construction
So far so good, but in terms of construction, spark plugs may not be quite as simple as you think. In fact, they are precision pieces of equipment. Thanks to the folks at Champion Spark Plug, we can provide you with a complete breakdown of the various plug features. Keep in mind that the vast majority of spark plugs offer similar (although not necessarily identical) construction.
 
In the accompanying photos, you can see what many of the above spark plug features actually look like. Check them out:
 
Ribs: Insulator ribs provide added protection against secondary voltage or spark flashover and also help to improve the grip of the rubber spark plug boot against the plug body.
 
Insulator: The insulator body is molded from aluminum oxide ceramic. In order to manufacture this part of the spark plug, a high pressure, dry molding system is utilized. After the insulator is molded, it is kiln-fired to a temperature that exceeds the melting point of steel. This process results in a component featuring exceptional dielectric strength, high thermal conductivity and excellent resistance to shock.
Spark Plug Insulator
The pointer shows the spark plug insulator. As mentioned above, it is formed from aluminum oxide ceramic. The outer surface is ribbed to provide grip for the spark plug boot and to simultaneously add protection from spark flashover (crossfire).
Hex: The hexagon provides the contact point for a socket wrench. The hex size is basically uniform in the industry and is generally related to the spark plug thread size.
 
Shell: The steel shell is fabricated to exact tolerances using a special cold extrusion process. Certain types of spark plugs make use of a steel billet (bar stock) for shell construction.
 
Plating: The shell is almost always plated. This enhances durability and provides for rust and corrosion resistance.
Spark Plug Steel Shell
The steel shell is fabricated to exact tolerances using a special cold extrusion process or in other specialized cases, machined from steel billet. The hexagon machined onto the shell allows you to use a socket wrench to install or remove the plug.
Gasket: Certain spark plugs use gaskets while other examples are “gasketless.” The gasket used on spark plugs is a folded steel design that provides a smooth surface for sealing purposes. Gasketless spark plugs use a tapered seat shell that seals via a close tolerance incorporated into the spark plug.
 
Threads: Spark plug threads are normally rolled, not cut. This meets the specifications set forward by the SAE along with the International Standards Association.
 
Ground Electrode: There are a number of different ground electrode shapes and configurations, but for the most part, they are manufactured from nickel alloy steel. The ground electrode must be resistant to both spark erosion as well as chemical erosion, both under massive temperature extremes.
Spark Plug Ground Electrode
There are a number of different ground electrode shapes and configurations, but for the most part, they are manufactured from nickel alloy steel.
Center Electrode: Center electrodes must be manufactured from a special alloy that is resistant to both spark erosion and chemical corrosion. Keep in mind that combustion chamber temperatures vary (and sometimes radically). The center electrode must live under these parameters.
Spark Park Electrode Gap
The area between the ground electrode and the center electrode is called the gap. Center electrodes must be manufactured from a special alloy that is resistant to both spark erosion and chemical corrosion.
Spark Plug Insulator Nose
Insulator Nose: There are a large number of insulator nose shapes and sizes available, but in essence, the insulator nose must be capable of shedding carbon, oil and fuel deposits at low speeds. At higher engine speeds, the insulator nose is generally cooled so that temperatures and electrode corrosion are reduced.

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