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Spark Plug Guide

Spark Plug Guide - from Cyclepedia



contents:

Threads

There are currently three spark plug thread diameter and pitch sizes used on motorcycles and ATVs: 10 mm x 1.0, 12 mm x 1.25 and 14 mm x 1.25. There are currently two thread reaches (lengths) used: 1/2 inch  and 3/4 inch.

doc20040726235413

Never use a spark plug of the wrong reach. If the reach is too short, carbon deposits can build up on the threads of the spark plug hole, plus the spark will not properly ignite the air/fuel mixture. If the reach is too long, the piston could contact the spark plug, plus carbon deposits can build up on the spark plug threads.

Wrenches

There are currently three spark plug wrench sizes used on motorcycles and ATVs, 5/8 “, 18 mm and 13/16″.

Spark Plug Parts

sparkplugparts

Spark Plug Codes

Spark plug codes tell a lot of useful information about the spark plug, however, each spark plug manufacturer uses different codes. Here are the most common spark plug codes by brand.

NGK

NGK is the largest manufacturer of spark plugs for motorcycles and ATVs in the world, and come as original equipment on many vehicles. Here is an example of their basic spark plug code.

DPR8EA-9

The first letter of the NGK spark plug code (in this case a “D”) indicates the thread size of the spark plug. There are three spark plug thread sizes currently being used in motorcycles and ATVs. “B” indicates a 14 mm x 1.25 pitch size, “D” indicates a 12 mm x 1.25 size and “C” indicates a 10 mm x 1.0 size. The letter “J” indicates a 12 mm x 1.25 size with two ground electrodes.

The “P” indicates a projected tip spark plug design that moves the spark deeper into the combustion chamber. The letter “K” in this location would indicate a 3/8″ hex (wrench) size.

Note; Do not use a projected tip spark plug where it is not called for as it could contact the piston and cause catastrophic engine damage.

The “R” indicates a resistor type spark plug. Resistor type spark plugs reduce the amount of radio frequency interference (rfi) that can cause ignition misfires and static on the radio, if so equipped. The letter “U” in this location would indicate a surface discharge gap (no ground electrode).

The first number (8 in this example) indicates the heat range of the spark plug, the higher the number the colder the heat range. Generally speaking, a colder heat range is used under high temperature conditions such as racing, while a hotter heat range is used under colder climate conditions. It is best to use the heat range specified by the manufacturer.

The letter “E” indicates the reach of the spark plug, that is, the length of the threads. There are two size reaches currently being used in motorcycles and ATVs. “H” indicates a 1/2″ reach, while “E” indicates a 3/4″ reach.

The letter “A” indicates some type of special feature. The letter “B” or “C” in this location indicates a spark plug designed for racing applications. The letter “G” indicates a fine wire nickel alloy center electrode. The letters “GV” indicate a gold palladium center electrode. The letters “IX” indicate an iridium center electrode. The letter “P” indicates a platinum center electrode. The letter “S” indicates a copper center core. The letter “V” indicates a fine wire gold palladium center electrode. The letter “Y” indicates a V-grooved center electrode.

The number after the – indicates the recommended spark plug gap in tenths of a millimeter. A -8 should be gapped to .8 mm or .032″, -9 should be gapped to .9 mm or .035″, -10 should be gapped to 1.0 mm or .040″ and -11 should be gapped to 1.1 mm or .044″. If there is no number at the end of the spark plug code, it should be gapped to .7 mm or .028″ unless specified differently by the vehicle manufacturer.

Nippon Denso (ND)

Here is an example of the Nippon Denso basic spark plug code.

X24EPR-U10

The first letter of the ND spark plug code (in this case an “X”) indicates the thread size of the spark plug. There are three size spark plug threads currently being used in motorcycles and ATVs. “W” indicates a 14 mm x 1.25 pitch size, “X” indicates a 12 mm x 1.25 size and “U” indicates a 10 mm x 1.0 size.

The number (24 in this example) indicates the heat range of the spark plug, the higher the number the colder the heat range. Generally speaking, a colder heat range is used under high temperature conditions such as racing, while a hotter heat range is used under colder climate conditions. It is best to use the heat range specified by the manufacturer.

The letter “E” indicates the reach of the spark plug, that is, the length of the threads. There are two size reaches currently being used in motorcycles and ATVs. “F” indicates a 1/2″ reach, while “E” indicates a 3/4″ reach.

The “P” indicates a projected tip spark plug design (1.5 mm projection) that moves the spark deeper into the combustion chamber. The letter “S” in this location indicates it is a standard (non-projected tip) type, while the letter “X” indicates a 2.5 mm projected tip.

Note; Do not use a projected tip spark plug where it is not called for as it could contact the piston and cause catastrophic engine damage

The “R” indicates a resistor type spark plug. Resistor type spark plugs reduce the amount of radio frequency interference (rfi) that can cause ignition misfires and static on the radio, if so equipped.

The “-U” indicates that the ground electrode has a U groove made into it to provide a better initial flame kernel. The letters “P” or “V” would indicate a platinum electrode.

The number at the end indicates the recommended spark plug gap in tenths of a millimeter. An 8 should be gapped to .8 mm or .032″, 9 should be gapped to .9 mm or .035″, 10 should be gapped to 1.0 mm or .040″ and 11 should be gapped to 1.1 mm or .044″. If there is no number at the end of the spark plug code, it should be gapped to .7 mm or .028″ unless specified differently by the vehicle manufacturer.

Champion

Here is an example of the Champion basic spark plug code.

RL82YC

The “R” indicates a resistor type spark plug. Resistor type spark plugs reduce the amount of radio frequency interference (rfi) that can cause ignition misfires and static on the radio, if so equipped.

The second letter of the Champion spark plug code (in this case an “L”) indicates the thread size and reach of the spark plug. There are three size spark plug threads and two reaches currently being used in motorcycles and ATVs. “L” indicates a 14 mm x 1.25 pitch size with a 1/2″reach. “N” indicates a 14 mm x 1.25 with a 3/4″ reach. “P” indicates a 12 mm x 1.25 with a 1/2″ reach. “A” indicates a 12 mm x 1.25 with a 3/4″ reach. “Z” indicates a 10 mm x 1.0 with a 1/2″ reach. “G” indicates a 10 mm x 1.0 with a 3/4″ reach.

The number (82 in this case) indicates the heat range of the spark plug, the higher the number the hotter the heat range (opposite of NGK and ND spark plugs). Generally speaking, a colder heat range is used under high temperature conditions such as racing, while a hotter heat range is used under colder climate conditions. It is best to use the heat range specified by the manufacturer.

The letters after the heat range can indicate a number of things. The letter “B” indicates two ground electrodes. The letter “C” indicates a copper core. The letter “G” indicates a precious metal center electrode. The letters “H” or “Y” indicate a projected tip. The letter “P” indicates a platinum center electrode.

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