NGK© Spark Plug Codes ( ST1100\ST1300 ) *

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NGK© Spark Plug Codes

Here is the table of values for NGK© spark plug names.

The breakdown is like this: (B) (CPR) (6) (E) (S) - (11)
Six fields.  Some, e.g. the second field, are optional.
Some fields may have multiple letters.

Field one: Thread diameter.
 A = 18mm     B = 14mm      C = 10mm        D = 12mm

Field two: Construction.
 C = hex size 5/8"                  K = hex size 5/8 with projected tip (ISO)
 M = compact type                 P = projected insulator type
 R = resistor                          SD = surface discharge for rotary engines
 U = semi-surface discharge    Z = inductive suppressor

Field three: Heat Range.
 2 = hot, up to 10 = cold.  There's no 1

Field four: Thread reach.
 E = 19mm                 F = tapered seat
 H = 12.7mm (1.5")     L = 11.2mm (7/16")

 If this field is blank, an 18mm diameter plug has 12mm reach,
 and a 14mm plug has a 9.5mm (3/8") reach.

Field Five: Firing end construction.
 A, B = special design (no details given)
 C = special ground electrode
 G = racing use
 GV = racing use V type
 H = half thread
 K = 2 ground electrodes for certain Toyotas
 L = half heat range
 LM = compact lawn mower type
 M = 2 ground electrodes for Mazda rotary engine
 N = special ground electrode
 P = platinum tip (premium)
 Q = 4 ground electrodes
 R = delta ground electrode for BMW
 S = standard 2.6mm centre electrode
 T = 3 ground electrodes
 V = fine-wire centre electrode, gold palladium
 V = platinum tip (high performance)
 W = tungsten electrode
 X = booster gap
 Y = v-groove centre electrode

Field Six: (after the dash) Wide gap.
 8 = .032"              9 = .036"                10 = .040"
11 = .044"             there is no 12          13 = .050"
14 = .055"             15 = .060"               20 = .080"


Other notes:
There's more, such as for metal shell plugs, "V-Power" plugs
for North American made cars, and other stuff.  I'm not typing it in.

Some Motorcycle-related comments:
Some bikes use the DR8ES-L plug.  There's no indication what the 'L'
means; it does not appear in the symbol chart for field six.

ST1100\ST1300: CR8EH-9  CR8EHVX-9 ( Plug gap: 0.035" )

Extended-life platinum tip plugs replacing the CR9EH-9 are
available as CR9EHVX-9.

SPECIAL NOTE:  CR8EHVX-9 superseded to CR8EHIX-9, Also known as NGK 3797 as most retailers now list these as.

Resistor plugs are used for two reasons:
1. They cut down electrostatic interference.

2. They provide a sharper "edge" to the voltage spike, making for
   a stronger, shorter spark. On high RPM motors, this is important.

The projected insulator simply describes the shape of the plug head.
A projected insulator sticks out a little further into the combustion
chamber.

More info at NGK© Spark Plugs USA.