Spark Plugs: Have you been inspecting and replacing them?

The sparks plugs mounted in the engine's

combustion chamber play a critical role by igniting
the fuel-air mix.
Gasoline engines obtain power by compressing a fuel-air mixture of
air and gasoline, then exploding this mixture by ignition. Spark plugs
serve to ignite this fuel-air mixture. With the battery as the power
source, the spark plug converts the electrical energy that comes
through the ignition coil and distributor into a spark which ignites the
fuel air mixture. In other words, without the spark plug, the engine
doesn't run; the spark plug is a important part because its
performance influences the overall performance of the engine.

INTRODUCTION

Problems like these can occur!

· Starting is not so good.
· Fewer horsepower.
· Idling becomes rough.
· Mileage becomes worse.

When to Replace Spark Plugs

If the center electrode tip becomes worn out into a Cars: 15,000 to 20,000km
round shape, it is possible that the sparks produced
Small Car(6600cc)s: 7,000 to 10,000km
are not as effective, resulting in the fuel-air mixture
being ignited less steadily. If this happens, engine Motorcycles: 3,000 to 5,000km
horsepower decreases fuel consumption becomes * Service lifetime is an approximate guideline. Depending on
the ignition system of the vehicle, the service lifetime may
worse, and engine lifetime may be negatively affected; become shorter.
we recommend regular replacement of spark plugs. Results of Spark Plug Replacement
· Improved Mileage
· Better Starting
· Better Acceleration
Spark plug heat dispersal
The heat that the electrode section of the spark plug
receives due to combustion is dispersed through the
path in the figure.

The degree to which a spark plug disperses the heat it

receives is called its "heat range". Spark plugs with a
high degree of heat dispersal are called high heat range
(cold type) and those with a low degree of heat dispersal
are called low heat range (hot type).
This is largely determined by the temperature of the gas
inside the combustion chamber and the spark plug
design.
Low heat range and high heat range
Low heat range plugs have long insulator leg sections
and the surface area affected by the flame and the gas
pocket capacity are large.
Also, since the heat release path from the insulator leg
section to the housing is long, heat dispersal is low and
the temperature of the center electrode rises easily.
On the other hand, high heat range plugs have short
insulator legs and the surface area affected by the flame
and the gas pocket capacity are small.
Also since the heat release path from the insulator leg
section to the housing is short, heat dispersal is high and
the temperature of the center electrode does not rise
easily.

Spark plug temperature and vehicle speed (1)

The relationship between the spark plug temperature
and vehicle speed and heat range is expressed with a
graph like that in the figure. There are restrictions on the
temperatures at which spark plugs can be used: the
lower limit is the self-cleaning temperature and the upper
limit is the pre-ignition temperature.A spark plug only
functions completely when its center electrode
temperature is between these temperatures of about
500°C and 950°C.
Spark plug temperature and vehicle speed (2) - self-cleaning temperature
When the center electrode temperature is 500°C or
lower, free carbon generated when the fuel does not
combust completely is deposited on the surface of the
insulator. Therefore, the insulation between the insulator
and the housing falls, electricity leaks occurs, the spark
across the gap is incomplete, causes ignition failures.
This temperature of 500°C is called the self-cleaning
temperature because above this temperature the carbon
is naturally burnt away completely by combustion.

Spark plug temperature and vehicle speed (3) - pre-ignition temperature

When the center electrode reaches 950°C or higher, pre-
ignition (early ignition) occurs, meaning that the
electrode serves as a heat source and ignition occurs
without a spark. Therefore, output falls and this can
reach the level of electrode wear and insulator damage.
Spark plug temperature and vehicle speed (4)
Low heat range spark plugs have center electrode
temperatures that rise easily and even at low-speed,
they easily reach the self-cleaning temperature, so
carbon is not deposited easily on the insulator section.
On the other hand, high heat range spark plugs have
center electrode temperatures that do not rise easily, so
they are unlikely to reach the pre-ignition temperature
even at high speed.
Therefore, this type of spark plug is generally used for
high speed, high output engines.
That is why it is necessary to select spark plugs with the
appropriate heat range for the engine characteristics,
running conditions, etc.

Recommended Torque and Tightening Angle for DENSO plugs.

Use the correct wrench for the hex on the plug, and be careful not to damage the insulator.
When changing, make sure that the oil, etc. on the outside of the plug does not enter the engine
interior.
When putting the plugs in, clean the engine side of the flange, and put in the plugs after making
sure the gasket is in the flange.
Make sure the plugs are vertical, and tighten them by hand until they cannot be tightened any
further.
Then, use a plug wrench to tighten them accurately to the torque or rotation angle showed in the
chart below.
 If a thread lubricant such as grease is coated on the thread, tightening to the recommended
torque is tightening too much;
this has been linked to seal leakage.
Do not use a thread lubricant.
Tightening more than the tightening angles and torques shown on the right could result in
damage to the engine and furthermore could result in the plug coming off at the thread.

Recommended Recommended Tightening Angle

Thread Size Applicable Models
Torque New Plug Previously Used
M8 All Types 8-10N ・m About 1 turn About 1/12 turn
Types other than the ones shown
M10 10-15N ・m About 1/3 turn About 1/12 turn
below
M10 UFE, IUH, VUH, VNH Types 10-15N ・m About 2/3 turn About 1/12 turn
M10 Stainless Gasket Type（*1） 10-15N ・m About 3/4 turn About 1/12 turn
M12 All Types 15-20N ・m About 1/3 turn About 1/12 turn
Types other than the ones shown
M14 20-30N ・m About 1/2 turn About 1/12 turn
below
M14 Stainless Gasket Type（*2） 20-30N ・m About 2/3 turn About 1/12 turn
M18 All Types 30-40N ・m About 1/4 turn About 1/12 turn

M14 Taper
All Types 20-30N ・m About 1/16 turn About 1/16 turn
seat
(*1)IUH27ES, U24FER9S
(*2)PK22PR-L11S, SK22PR-M11S, IK16G, IK20G, IK22G, VK16G, VK20G, VK22G, K20PR-SU9, SK20PR-L9S,
SKJ20DR-M11S, KJ20DR-M11S, K20PR-L11S

Spark
When the high voltage produced by the ignition system
is applied between the center electrode and ground
electrode of the spark plug, the insulation between the
electrodes breaks down, current flows in the discharge
phenomenon, and an electrical spark is generated.

This spark energy trigger ignition and combustion in the

compressed air-fuel mixture. Watching the motion picture (QuickTime About 1.4MB)
*The motion picture will be displayed on another window.
This discharge is of extremely brief duration (about
1/1000 of a second) and is extraordinarily complex.
The role of the spark plug is to reliably generate a strong
spark between the electrodes accurately at the specified
time to create the trigger for combustion of the gas
mixture.

Ignition
Ignition by electrical spark occurs because the fuel
particles between the electrodes are activated by the
spark to discharge, a chemical reaction (oxidation) is
triggered, the heat of reaction is generated, and the
flame core is formed. This heat activates the surrounding
air-fuel mixture, eventually a flame core is formed that
spreads the combustion to the surroundings itself.

However, if the quenching effect between the electrodes

(the work of the electrodes absorbing the heat and
extinguishing the flame) is greater than the flame core
heat generation action, the flame core is extinguished
and the combustion stops.

If the plug gap is wide, the flame core is larger and the
quenching effect is smaller, so reliable ignition can be
expected, but if the gap is too wide, a large discharge
voltage becomes necessary, the limits of the coil
performance are exceeded, and discharge becomes
impossible.

Change in the discharge voltage

The ignition system normally generates 10-30 kV secondary voltage.

Click the number of the text.

 1. When the primary current is cut off at the 'a' point, the secondary voltage rises.
2. At the 'b' point, partway through the rise in voltage, the spark plug reaches the discharge voltage
and a spark is generated between the electrodes.
3. Between 'b' and 'c' is called the capacitance spark. At the start of the discharge, the spark is
generated by the electrical energy stored in the secondary circuit. The current is large but the
duration is short.
4. Between 'c' and 'd' is called the inductance spark. The spark is generated by the electromagnetic
energy of the coil. The current is small but the duration is long. From the 'c' point, the discharge is
continued for about 1 millisecond and at the 'd' point, the discharge ends.

The discharge voltage changes drastically with various conditions.

The three factors with particularly large impact are the spark plug gap, the compression pressure, and the air-
fuel mixture temperature.

Spark plug gap

The discharge voltage rises in proportion to the spark
plug gap.
The spark plug gap widens bit by bit as the electrode
wears, so high discharge voltage becomes necessary
and misfire occurs more easily.

Electrode shape
Even for the same spark plug gap, if there are edges on
the electrode, discharge occurs more easily.
Older spark plugs have electrodes that have rounded, so
discharge becomes more difficult and misfire more likely.

Compression pressure
The discharge voltage rises in proportion to the
compression pressure.
The compression pressure is higher for low speed and
high load. Sudden acceleration for starting out fits these
conditions, so higher voltage is required then and misfire
occurs more easily.

Air-Fuel mixture temperature

The discharge voltage drops as the air-fuel mixture
temperature rises.
The lower the engine temperature, the higher the
required voltage, so misfire occurs more easily at low
temperature.

Electrode temperature
The discharge voltage drops as the electrode
temperature rises.
The electrode temperature rises in proportion to the
engine speed, so misfire occurs more easily at low
speed.

Air-Fuel ratio
There is a tendency for the discharge voltage to be
higher the leaner the air-fuel mixture (the larger the air-
fuel ratio).
If the air-fuel mixture becomes leaner due to fuel system
trouble misfire occurs more easily.

Humidity
As the humidity rises, the electrode temperature
decreases, so the discharge voltage becomes slightly
higher.

<< back to Spark and Ignition

The effect on the spark plugs of ignition and combustion of the running engine is severe and various aspects of
performance for withstanding this are required.

Heat-proof
Can withstand sudden heat and sudden cold
The temperature received by the inside surface of the spark plug reaches as high as 2000°C during
combustion of the air-fuel mixture and during the intake stroke, the spark plug is subject to sudden cooling by
low-temperature gas. In 4-cycle engines, this sudden heating and sudden cooling is repeated every other
rotation as long as the engine is running.
As the same time that it must provide such capacity to withstand heat, the spark plug must also give off enough
heat to avoid becoming a starting point for surface ignition.

Mechanical strength
Can withstand severe pressure changes.
In the intake stroke, the pressure is less than 0.1MPa, but in the combustion stroke it reaches 4.5MPa or
higher. The mechanical strength to withstand this severe pressure change is required.

Insulation
Has insulation at high voltage
In an environment in which the temperature and pressure are constantly changing drastically, spark plugs must
have adequate insulation to withstand high voltages that reach about 10-30kV.
Air-tightness
Maintains an airtight seal in a harsh environment
Spark plugs must maintain an airtight seal between the housing and the insulator under conditions of drastic
temperature and pressure change and high voltage.
Denso's heat staking process provides stable air tightness.

Wear-proof
Minimizes electrode wear
Spark plugs must have the wear-proof resistance to minimize electrode wear in a severe usage environment.
Denso's patented iridium alloy is effective against wear.

Soot-proof
Minimizes soiling from combustion
It is required that under severe usage conditions, spark plugs minimize soiling of electrodes by the combustion
of the air-fuel mixture and have self-cleaning that burns away carbon deposits with heat.
Therefore, it is desirable that the spark plug temperature rise quickly even when the vehicle is moving at low
speed and that the insulator section reach the self-cleaning temperature (about 500°C).

Various circumstances such as engine conditions and driving conditions are rough measures for
choosing a plug. For example, if strenuous driving is continued for a long time using normal plugs,
the plug will overheat.
This is why the idea of a regular plug for a regular car doesn't work.
What's important is to inspect the condition of your current plugs, and then choose a plug
accordingly.

The heat range will change with the seasons.

When the air temperature is high, as in the summer, the inlet air temperature becomes higher,
increasing the load on the engine. In times like this, it's better to choose a plug with a higher heat
range.
The more horsepower is increased, the higher the required heat range.
If the horsepower has been increased through tuning, the increase in explosive power leads to an
increase in combustion chamber temperature, making pre-ignition more likely; in such cases it is
necessary to choose a plug with a higher heat range and a higher level of heat resistance.
The Parts of the Spark Plug

(Example)Resistor Platinum Plug

Insulator
Insulates the terminal, center shaft and center electrode from the housing,
preventing escape of high voltage from the electrodes.
Since the bottom of the insulator projects into the combustion chamber, high
purity alumina with superior heat-proof characteristic, mechanical strength,
excellent insulation and thermal conductivity at high temperature, etc. is used.

Terminal
 The terminal is connected to a high-tension cord through which high-voltage
current from the ignition system flows.
A terminal nut is installed so this type can support almost any high-tension cord
in the world. For vehicles not requiring a terminal nut, the terminal can be
removed.

Ring, packing washer

Makes the insulator and the housing fit tightly to each other and maintains the
airtightness.

Center shaft (stem)

Center shaft connecting the terminal and the center electrode.
This shaft is made of steel and has the role of allowing high-voltage current to
flow from the terminal to the center electrode without loss.

Housing
The housing forms an outer shell that surrounds the insulator, supports the
insulator, and installs the spark plug in the engine.
At the bottom the ground electrode is located, so current can flow through the
engine itself to the center electrode over the gap.

Glass Seal
Mounted between the center shaft and insulator to maintain the airtightness.
Denso uses the glass seal method.
A special mixture of glass powder and copper powder is charged in the
installation section for the insulator and center shaft and center electrode and
melted at high temperature. This bonds the center shaft and the center electrode
and fuses the insulator and the metal.
The sealing for both is good and the thermal ratio of expansion is appropriate, so
even under harsh conditions gaps do not occur and good airtightness can be
secured.

Gasket
 Makes the housing and the engine fit tightly to each other and maintains the
airtightness of the combustion chamber.
There is a procedure for tightening and the appropriate tightening margin must
be secured.

Electrode with copper

Special nickel alloy is used for the center electrode to reduce electrode wear.
Copper is sealed into the center section to improve thermal conductivity.

Ring, packing washer

Makes the insulator and the housing fit tightly to each other and maintains the
airtightness.

Center Electrode
A new iridium alloy tip with a diameter of 0.4 mm is laser welded to the tip of the
center electrode to make the center electrode.
This lowers the spark voltage, secure reliable spark, reduces the quenching
effect, and improves ignition performance.
Iridium, like platinum, is a precious metal and has extraordinarily superior
properties for a spark plug electrode, for example high-temperature withstand,
high strength, and low resistance. In order to further improve oxidation
resistance at high temperatures, Denso developed a unique new iridium alloy
containing rhodium.

U-groove ground electrode

Nickel chrome material is used for the ground electrode and various measures
are taken with the shape to improve ignition performance.
One of these measures is the U-groove.

1. The surface contacted by the air-fuel mixture is large,

2. There is much edge section, and sparks occur easily.
3. The flame core (flame size) widens easily.

There are many other features as well and large ignition energy can be
obtained.
Denso obtained patents for spark plug U-grooves from 1975 to 1992.

Tapered cut ground electrode

 The ground electrode has a shape in which the electrode tip is cut to a finely
tapered shape.
This reduces the quenching effect, so it improves ignition performance

Electrode wear
The electrode wears from the locations that discharge
easily with spark discharge.
In particular, since the center electrode reaches high
temperatures, it oxidizes and wears.
The amount of electrode wear varies with the electrode
material melting point, strength, hardness, etc. In order
to reduce the amount of this wear, nickel alloys,
platinum, iridium, and other such materials are used for
the electrodes and service lives are also extended with
fine electrodes.
Also, the wear varies with the engine type and usage
conditions, but for normal plugs, it is approximately in the
range of 0.10-0.15mm for each 10,000km driven.

Rise in required voltage

The required voltage (the voltage required to discharge
across the gap) rises in proportion to the distance driven.
This rise in the required voltage is large until the sharp
section at the end of the center electrode is worn round
to some degree (about 4,000km). After that, the main
factor is the enlargement of the gap due to electrode
wear and the rise in the required voltage is smaller.

Misfiring and its cause

Failure : Air-Fuel mixture does not burn.
Failure due to sparks not discharging between the electrodes of the spark plug.
Spark failure : This occurs when the voltage generated by the ignition coil is lower than the
voltage required by the spark plug.
Ignition Sparks discharge between the electrodes of the spark plug but the air-fuel
:
failure mixture does not ignite and burn.
Economic service life

The physical service life for a spark plug can be thought of as the number of kilometers driven until the spark
plug begins to misfire. Misfiring causes not only wastage of fuel, but also irregular engine vibration and output
drop. In particular, for vehicles with emissions controls, misfiring can damage the catalytic converter, so using a
spark plug all the way to the end of its physical service life is inexpedient economically.
Therefore, as the economical replacement interval, replacement after the number of kilometers in the figure
above is recommended. (However, 100,000km for platinum spark plugs.)

Diagnosing the state of the spark plugs is an effective method for elucidating the cause of engine troubles.

Normal
The insulator leg section has light gray or tan
deposits and slight electrode erosion.

Trouble
The flowing trouble can be caused by engine defects.
Engine trouble

Case 1 Case 2
· Starting defect · Misfiring only when running at
· Misfiring when idling high speed or when accelerating
· Misfiring during normal running suddenly
Diagnosis >> Diagnosis >>
Case 3 Case 4
· Loss of power when running at
· Trouble other than with the
high speed or under high load
engine
Piston breakdown
Diagnosis >>
Diagnosis >>
Spark plug state

Case 1
· Starting defect
· Misfiring when idling
· Misfiring during normal running

[Appearance]
The insulator foot section and electrode section
are covered with dried, soft black carbon.
[Results]
Poor starting, misfiring, acceleration defect.
[Cause]
Repeated short-distance driving (driving with the
engine cool), incorrect choking (overly rich air-
fuel mixture), injection timing delay, plug heat
range too high.

[Appearance]
The insulator section and electrode section is
black and lustrous with wet oily deposits.
[Results]
Poor starting and misfiring.
[Cause]
Oil leaking due to piston ring, cylinder, or valve
guide wear (occurs easily to new engines and
engines that have just been overhauled), high
oil content in air-fuel mixture.(2-stroke engines)

[Appearance]
The spark plug is wet with gasoline immediately
after it is removed, but it soon dries off.
[Results]
Poor starting and misfiring.
[Cause]
The air-fuel ratio is too rich and is not igniting.
(Among the ways this can happen is if the driver
presses the accelerator over and over while
starting the vehicle.)
 [Handling]
Remove all the spark plugs, crank the starter
motor to bring fresh air into the cylinder and
make the air-fuel ratio leaner.

[Appearance]
The center and ground electrodes are rounded
and the gap has become too wide.
[Results]
Poor starting and acceleration.
[Cause]
Inadequate maintenance. (spark plug has
exceeded its service life.)

[Appearance]
The gap is wider than appropriate.
[Results]
Poor starting and acceleration.
[Cause]
The gap is inappropriate; the wrong spark plug
was selected. [Handling]
Remove all the spark plugs, crank the starter
motor to bring fresh air into the cylinder and
make the air-fuel ratio leaner.

[Appearance]
Insulator cracked
[Results]
Shorts due to insulation defect, causes poor
idling and misfiring during acceleration.
[Cause]
Spark plug removed/installed incorrectly. (spark
plug turned too far with spark plug wrench,
excess tightening torque, or other inappropriate
work.)
[Handling]
Remove all the spark plugs, crank the starter
motor to bring fresh air into the cylinder and
make the air-fuel ratio leaner.
<< back to Page Top

Case 2
· Misfiring only when running at high speed or when accelerating suddenly

[Appearance]
The insulator leg section has yellow or
yellowish-brown burnt on deposits or is covered
with a glossy surface.
[Results]
Misfiring during rapid acceleration or under high
load, but no problem in normal running.
[Cause]
Use of gasoline with much lead.
<< back to Page Top
Case 3
· Loss of power when running at high speed or under high load
· Piston breakdown

[Appearance]
The insulator leg section is scorched extremely
white with small black deposits. Rapid electrode
wear.
[Results]
Loss of power when running at high speed or
under high load.
[Cause]
Spark plug incorrectly tightened, engine cooling
problem, ignition timing too early, spark plug
heat range too low, severely abnormal
combustion.

[Appearance]
The center electrode or ground electrode is
melted or scorched. There are spots on the
insulator leg section and deposits of aluminum
or other metal powder.
[Results]
Power loss due to engine damage.
[Cause]
Often this is due to overheating; pre-ignition is a
phenomenon in which combustion occurs before
ignition.
The plug heat range is too low, the injection
timing is too advanced, etc.

[Appearance]
The insulator leg section is cracked or broken.
[Results]
Misfiring
[Cause]
Severely abnormal combustion, lack of attention
to gap adjustment.

[Appearance]
Housing installation screw section melting.
[Results]
Power loss due to engine damage.
[Cause]
Incorrect spark plug tightening.

[Appearance]
The electrode is bent and the insulator leg
section is broken. Indentations are sometimes
seen on the electrode.
[Results]
Misfiring.
[Cause]
The spark plug thread reach is too long for the
 engine head or there is some kind of foreign
matter (a small bolt, nut, or the like) in the
combustion chamber.

[Cause]
Overheating of the ground electrode and severe
engine vibration.

<< back to Page Top

Case 4
· Trouble other than with the engine

[Appearance]
Brown deposits on the insulator directly above
the housing
[Results]
No impact on the spark plug performance
[Cause]
This occurs due to electrical stress in the air
near the insulator. (This is not a spark plug gas
leak, for which it is sometimes mistaken.)

Thread Diameter and Hex Size

< Thread Diameter x Hex Size > (mm)

M --- 18 x 25.4 (Reach: 12mm) SK+ --- 14 x 16 (0.7mm diameter miniature iridium
L --- 18 x 22.2 (Reach: 12mm) plug)

MW --- 18 x 20.6 (Reach: 12mm) SKJ*+ --- 14 x 16 (Projected 0.7mm diameter

miniature iridium plug)
MA --- 18 x 20.6 (Tapered seat, Reach: 12mm)
SV --- 0.4mm diameter iridium with platinum
FK+ --- High Ignitability Plug (0.55mm Ir center
ground electrode
electrode, Pt ground electrode)
T --- 14 x 16.0 (Tapered seat)
J* --- 14 x 20.6 (Projected plug)
K+ --- 14 x 16.0 (Miniature plug) TR@ --- 14 x 20.6 (For marine applications)
KJ*+ --- 14 x 16.0 (Projected miniature plug) W --- 14 x 20.6
LP* --- 14 x 20.6 (Plug for LPG applications) --- 14 x 19.0 (Compact type)
P* --- 14 x 20.6 (Platinum plug) X --- 12 x 18.0
PK* --- 14 x 16 (Miniature platinum plug) XE --- 12 x 14.0
PKJ* --- 14 x 16 (Projected miniature platinum plug) XU --- 12 x 16.0
PQ* --- 14 x 16 (Miniature platinum plug) U --- 10 x 16.0
Q* --- 14 x 16 (Miniature plug) U --- 10 x 14.0 (U20M-U Only)
QJ* --- 14 x 16.0 (Miniature projected plug) N --- 10 x 16.0
QL* --- 14 x 20.6 (Miniature long cylinder housing Y --- 8 x 13.0
plug) Z --- 1/2PF x 23.8
S* --- 14 x 20.6 (0.7mm diameter iridium) Z --- 0.55 mm diameter iridium
S --- 14 x 20.6 (Surface gap plug (for RE * --- Reach: 19.0
engines)) + --- ISO compatible
@ ---Reach: 12.7

BACK TO TOP

Heat Range
DENSO NGK CHAMPION BOSCH

9 2 18 10

14 4 16,14 9

16 5 12,11 8

20 6 10,9 7,6

22 7 8,7 5

24 8 6,63,61 4

27 9 4,59 3

29 9.5 57

31 10 55 2

32 10.5 53

34 11

35 11.5

BACK TO TOP

Reach
A --- 19mm H --- 19.0mm
(Electrode position: 7mm) (Electrode position:
--- 21.5mm 8.5mm)

B --- 19.0mm --- 26.5mm

(Electrode position: 9.5mm) L --- 11.2mm
C --- 19.0mm M --- 8.6mm
(Electrode position: 5.0mm) N --- 17.5mm
D --- 19.0mm (Shroud: 2mm) (Taper seat,
E (With gasket) --- 19.0mm HALF THREAD)
20.0mm V --- 25.0mm
E (Taper seat) --- 17.5mm (Tapered seat)

F --- 12.7mm None --- 9.5mm

11.2mm
FE --- 19.0mm (Half thread)
19.0mm
G --- 19.0mm (Shroud: 2.8mm) 21.5mm
--- 19.0mm (Shroud: 3.0mm) None (Tapered seat) --- 8.3mm
11.2mm
11.2mm

BACK TO TOP

Shape (Type)

A --- Double ground electrodes N --- Racing type (Nickel electrode)

A --- Oblique ground electrode (For racing) Pt --- Racing type (Platinum electrodes)
Double ground electrodes with bent shape P --- Projected (1.5mm projection)
AY ---
(special) S --- Non-projected (0mm projection)
B --- Triple ground electrodes --- Iridium on a single side
BG --- Triple ground electrodes (shrouded) T --- Double ground electrodes
D --- Quadruple ground electrodes TM --- Double ground electrodes
K --- 1mm Insulator projection TN --- Double ground electrodes
LM --- Compact type (Hex size: 20.6mm) V --- Slant ground electrode
M --- Shortened insulator head length X --- Fully projected (2.5mm projection)
M --- Compact type (Hex Size: 19.0mm)

BACK TO TOP

Internal Construction

R --- With Resistor

None --- Without Resistor
< Exception >
S29A, S29 both have Resistors

BACK TO TOP

Shape (Type)

-A --- Special specification -N --- For Yamaha and Kawasaki

-B --- Special specification -P --- Ground electrode has a double layer of
-C --- Cut-back ground electrode platinum

-E --- Special specification --- Center or ground electrode has platinum

-F --- Special specification -S --- Semi-surface gap discharge type

-G --- Grease applied on to threads, for CNG -S --- Stainless gasket

applications -TP --- Platinum on center electrode, with taper cut
-GL --- Platinum center electrode ground electrode

-L --- For CVCC, with a withdrawn insulator -U --- U-cut ground electrode

--- 3.5mm projected insulator for motorcycles -US --- Star-shaped center electrode is used

--- Withdrawn insulator for motorcycles -V --- 1.3mm diameter nickel center electrode

--- Thin center electrode for motorcycles -Z --- Taper cut

--- Heat resistant ground electrode -ZU --- ZU Plug

-M --- Larger ground electrode

BACK TO TOP

Gap

5 --- 0.5mm (.020'')

8 --- 0.8mm (.032'')
9 --- 0.9mm (.035'')
10 --- 1.0mm (.040'')
11 --- 1.1mm (.044'')
13 --- 1.3mm (.050'')
14 --- 1.4mm (.055'')
15 --- 1.5mm (.060'')
20 --- 2.0mm (.080'')

< None > Cars: 0.8mm M.C: 0.7mm

< Exceptions > P16R, PQ16R, PQ20R are 1.1mm
 With Iridium Alloy Center Electrode Employing a high melting point
iridium alloy tip for the center electrode tip, a fine dia. of 0.4mm has
been realized. This fine electrode has led to a lower spark voltage and
a large increase in ignitability, which draws out even more output and
accelerator response from the engine.
(Melting Point: Iridium 2454°C, Platinum 1769°C).

Iridium plug | Platinum plug | Cars & trucks plugs | Motorcycle plugs

Iridium plug

Super ignition, 12 mm dia., long-reach shroud iridium plug

(Example) FXE20HE11
･ Super Ignition Plug
･ The needle-shaped ground electrode of this revolutionary iridium plug features
DENSO's own exclusive technology, resulting in an unparalleled reduction of quenching
effect.
･ Equipped as original parts on Nissan's TIIDA and NOTE
･ D12 L26.5 14
･ NISSAN

Super ignition, long-reach iridium plug

(Example) FK20HR11
･ Super Ignition Plug
･ With 0.55 mm diameter iridium center electrode and platinum ground electrode, this
iridium plug has a very long lifetime.
･ Equipped on TOYOTA's SIENTA and CROWN since 2003.
･ D14 L26.5 16
･ TOYOTA

Super ignition, iridium plug

(Example) FK16R11
･ Super Ignition Plug
･ D14 L19 16
･ TOYOTA

Long-reach iridium plug

(Example) SK16HR11, SK20HPR-L11
･ D14 L26.5 16
･ Honda / Toyota
New triple-electrode iridium plug
(Example) SK20BR11, SK20BGR11
･ Under normal operating conditions the main electrode sparks, but if it becomes fouled,
side electrodes generate the spark to burn off any carbon - this plug is the optimum
design for direct fuel-injection engines. Equipped as original parts for 3000 cc direct
injection engines (D-4) on TOYOTA's CROWN and other models.
･ D14 L19 16
･ TOYOTA

Iridium plug
(Example) SK20R11, SK16R-P11, SK20PR-A11, SK20PR-B11, SK16PR-E11,
SK20PR-F8, SKJ16CR-L11, SKJ16CR-A8
･ We developed a 0.7 mm diameter iridium alloy electrode, the first in the world.
Ignitability and lifetime have dramatically improved. The SK16R-P11 is equipped as
original parts on TOYOTA's CENTURY.
･ D14 L19 16
･ TOYOTA / HONDA / MAZDA / MITSUBISHI / HYUNDAI / SUZUKI

Iridium plug with stainless steel gasket

(Example) SK22PR-M11S, SK20PR-L9S
･ D14 L19 16
･ HONDA

Extended shroud iridium plug

(Example) SKJ20DR-M11S, SKJ20DR-M11
･ D14 L19 16
･ HONDA
* SKJ20DR-M11S with stainless steel gasket

12 mm long-reach iridium plug

(Example) SXU22HR9, SXU22HDR8, SXU16HPR9
･ D12 L26.5 16
･ DAIHATSU / ISUZU / MITSUBISHI

12 mm long-reach iridium plug

(Example) ZXE20HR13
･ With 0.55 mm diameter iridium center electrode and platinum ground electrode, this
iridium plug has a very long lifetime.
･ D12 L26.5 14
･ NISSAN

0.4 mm dia. iridium plug with platinum tip ground electrode

(Example) SVK20RZ11, SVK20RZ8, VK16PR-Z11, VK20PR-Z11, VK22PR-Z11,
VK24PR-Z11, VK27PR-Z11
･ D14 L19 16
･ DAIHATSU / MITSUBISHI / HONDA
0.4 mm dia. iridium plug with platinum tip ground electrode
(Example) VNH27Z, VNH24Z
･ D10 L(6.3 + 12.7) 16
･ Honda Motorcycles

0.4 mm dia. iridium plug with platinum tip ground electrode

(Example) VUH27D, VUH27ES, VUH24D
･ D10 L(6.3 + 12.7) 16
･ Honda Motorcycles
* VUH27ES with stainless steel gasket

0.4 mm dia. iridium plug

(Example) IXU22C
･ D12 L19 16
･ SUZUKI

0.4 mm dia. iridium plug

(Example) IUH27D, IUH24D
･ Supplied 0.4 mm diameter iridium plugs to Honda Motorcycles for the first time in the
world.
･ D12 L (6.3 + 12.7) 14
･ HONDA Motorcycles CBR900RR

0.4 mm dia. iridium plug

(Example) IU27D
･ D10 L19 16
･ YAMAHA Motorcycles YZFR-1
 With Iridium Alloy Center Electrode Employing a high melting point
iridium alloy tip for the center electrode tip, a fine dia. of 0.4mm has
been realized. This fine electrode has led to a lower spark voltage and
a large increase in ignitability, which draws out even more output and
accelerator response from the engine.
(Melting Point: Iridium 2454°C, Platinum 1769°C).

Iridium plug | Platinum plug | Cars & trucks plugs | Motorcycle plugs

Platinum plug

Platinum plug
(Example) PK20R11
･ Platinum is used for both the center and ground electrodes.
･ Mileage, drivability, and durability are improved by using a finer center electrode with a
platinum tip.
･ D14 L19 16
･ TOYOTA / DAIHATSU

Double-electrode platinum plug

(Example) PK20TR11, PK20PTR-S9
･ Platinum tip is mounted on both the center and ground electrodes.
･ The double-electrode structure reduces the voltage required for positive discharges.
･ D14 L19 16
･ TOYOTA / DAIHATSU

With Iridium Alloy Center Electrode Employing a high melting point

iridium alloy tip for the center electrode tip, a fine dia. of 0.4mm has
been realized. This fine electrode has led to a lower spark voltage and
a large increase in ignitability, which draws out even more output and
accelerator response from the engine.
(Melting Point: Iridium 2454°C, Platinum 1769°C).

Iridium plug | Platinum plug | Cars & trucks plugs | Motorcycle plugs
Cars & trucks plugs

Long-reach plug
(Example) K20HR-U11, K16HPR-U11
･ D14 L26.5 16
･ TOYOTA

ISO-compatible small hex plug

(Example) K16R-U11, K16PR-U11
･ Compatible with ISO standards
* SKJ20DR-M11S with stainless steel gasket
･ φ14 L19 16
･ TOYOTA, and others

Small hex plug

(Example) Q16R-U11, Q16PR-U11
･ By reducing the hex size (16 mm), this plug is lighter in weight.
･ D14 L19 16
･ TOYOTA, and others

Extended shroud plug

(Example) KJ20DR-M11, KJ20DR-M11S
･ D14 L19 16
･ HONDA

Extended plug
(Example) KJ20CR11, KJ16CR-U11
･ KJ20CR11: no U-Groove
KJ20CR-U: with U-Groove
･ D14 L19 16
･ MAZDA, MITSUBISHI

Extended plug
(Example) KJ20CR-L11
･ The tip of the ground electrode has a taper-cut, and the center electrode is made finer
for improved ignitability.
･ D14 L19 16
･ HONDA

Double-electrode semi-surface plug

(Example) W20ETR-S11
･ With this new supplementary gap, resistance to fouling is improved.
･ D14 L19 20.6
･ TOYOTA, DAIHATSU
Triple-electrode plug
(Example) K22PB, W20EPB
･ Durability is improved with three ground electrodes.
･ D14 L19 16 (K22PB)
･ AUDI / VW / CITROEN / FIAT / MERCEDES-BENZ / RENAULT

12 mm long-reach plug
(Example) XU22HR9
･ D12 L26.5 16
･ DAIHATSU

12 mm dia. plug
(Example) XU22EPR-U
･ By reducing the hex size (16 mm), this plug may be used in light vehicles. Thread
diameter is 12 mm.
･ D12 L19 16
･ SUZUKI / MITSUBISHI

12 mm diameter long-reach plug with 14 mm hex size

(Example) XE20HR-U9
･ D12 L26.5 14
･ RENAULT

Taper seat plug

(Example) T16EPR-U
･ This plug may be installed only in non-Japanese cars and has no gasket.
･ D14 L17.5 16
･ GM, Ford
 With Iridium Alloy Center Electrode Employing a high melting point
iridium alloy tip for the center electrode tip, a fine dia. of 0.4mm has
been realized. This fine electrode has led to a lower spark voltage and
a large increase in ignitability, which draws out even more output and
accelerator response from the engine.
(Melting Point: Iridium 2454°C, Platinum 1769°C).

Iridium plug | Platinum plug | Cars & trucks plugs | Motorcycle plugs

Motorcycle plugs

Compact head plug

(Example) W27EMR-C
･ Plug with compact insulator head
･ D14 L19 20.6
･ HONDA / SUZUKI

12 mm dia. shroud plug

(Example) X24GP-U
･ D12 L (19 + 3) 18
･ HONDA

12 mm dia. 19 mm plug
(Example) X24EPR-U
･ D12 L19 18
･ HONDA / SUZUKI / YAMAHA

10 mm dia. plug with half-sized threads and stainless steel gasket

(Example) U24FER9S
･ D10 L (6.3 + 12.7) 16
･ HONDA

10 mm dia. plug with half-sized threads

(Example) U27FER9
･ With its wider spark gap of 0.9 mm compared to conventional plugs (0.6 to 0.7 mm), this
plug has improved ignitability.
･ D10 L (6.3 + 12.7 16
･ HONDA
10 mm dia. double-electrode plug
(Example) U31ETR
･ With two ground electrodes, heat resistance is improved.
･ D10 L19 16
･ KAWASAKI / SUZUKI

10 mm dia. 19 mm plug
(Example) U27ESR-N
･ Increasing the projection length by 0.5 mm improves resistance to fouling.
･ D10 L19 16
･ YAMAHA / KAWASAKI / SUZUKI

10 mm dia. 12.7 mm plug

(Example) U20FSR-U
･ D10 L12.7 16
･ HONDA / YAMAHA / SUZUKI

8 mm dia. plug
(Example) Y27FER-C
･ D8 L (6.3 + 12.7) 13
･ HONDA