Spark Plug; Spark Plug Heat Range - Honda Motorcycle Service Manual

IGNITION SYSTEMS
SPARK PLUG
Due to the high voltage generated at the ignition coil, sparks
jump across the center electrode and side electrode of the
spark plug and ignite the fuel mixture in the combustion
chamber.
Use spark plugs of the proper size and heat range appropriate
for the engine, or the engine will not perform to its full poten-
tial and damage to the engine may occur.
Spark plug heat range
As the spark plug is constantly exposed t o the engine
combustion, heat must be dissipated in order to keep the
spark plug at a certain temperature at which carbon deposits
are burned off.
The capacity to dissipate heat is called "heating value" or
heat range.
It is important to install spark plugs of the proper heating
value because the combustion temperature varies according
to the engine type and driving conditions.
Hot type
.......
Heat is dissipated slowly.
C o l d type
.....
Heat is dissipated quickly.
T h e heating value indicated by a number:
Smaller number
......
Hotter type
Larger number
........
Colder type
If an improper cold type spark plug is installed, the spark
does not jump across the electrodes as easily and the
electrodes may become contaminated with oil/gasoline. If an
improper hot type is installed, it causes overheating or
preignition, and may result i n melted electrodes and/or a
hole i n the piston.
Optional spark plugs are often listed for Honda motor-cycles.
Replace the standard plug with an optional one when-ever
the heating value of the original plug does not comply with
the driving conditions.
There are several types of spark plugs, grouped according to
the heating value, thread diameter and construction, as shown
below.
JGK oluo
V: Narrow cenrei
9 (Cold
type1
K:
si d e
electrode
Number indicates
Thread die.
/
Remark Heating value Thread lengih Remark
the plug
gap.
"9":
0.9 mm
I
Heat dissipation.
&
18 mm
B: 14 mm
C:
l o
mm
I
HOT TYPE-
b
COLD TYPE
4 lHor type1
s f
6
P: Porcelain projected
type
R: Resistor soark d u a
/
Heat range of hot type and cold type
lination) '
'
Cold type heat ran&
E: 1 9 mm
H: 12.7 mm
-
I V )
Driving speed (kmihl-------
A. 2 : Special
type
S:
w t t h copper
wick
NIPPONDENSO plug
27
(cold
r y m i
projected type
dicaies that rhe
Date of Issue : March, 1995
o
HONDA MOTOR CO.,LTD.
23-
9