Honda CB160 Shop Manual page 93

5. 3 IGNITION CIRCUIT
by combustion. If lead oxide adheres to the igni-
tion section,
it
becomes a conductor, and consumes
a part of the voltage. The phenomenon described
in the previous section is generated. The spark
plug should be constracted in such a manner that
it will reduce such phenomenon as much as possible,
and the insulation and electrodes should not be
subjected to the effects of chemicals.
2. Spark plug construction
The general construction of spark plugs employed
in automotive vehicles is shown in Fig. 5. 29. The
center electrode (Fig.
5. 30)
is wrapped by an insu-
lator
(Fig. 5. 31) and the exterior surface is wrapped
by
metallic tube.
(Refer to Fig. 5. 28 thru 5. 31)
3. Heat characteristics of spark plugs
The heat characteristics of a spark plug and quality
will determine the performance of the plugs .as well
as the performance of the engine.
(a) Spark plug performance
The ignition section of the plug fitted to the
cylinder head is hindered by residue generated
from combustion gas or oil.entering the combustion
chamber during operation of the engine. This ad-
hesion acts as conduction on the insulation and
provides a shorting passage for high voltage current,
resulting in a weakened spark and lowered output
of the engine or complete stoppage of the engine.
To prevent such occurrences, the surface of the
ignition section should be heated to an extent that
the temperature burns the residue {approximately
450 to 600°C).
However, temperature differs in accordance to
the engine condition. Such temperature is termed
"·Selfcleaning temperature "
However, if the ignition section of the plug is
overheated, the ignition section becomes an ignition
point, resulting in pre-ignition and inducing knocks
which lower engine output. Hence, it is necessary
to keep the temperature of the ignition section
below the pre-ignition temperature which is appro-
ximately 800°C. However, this varies according
to engine conditions.
" The ignition section of a plug should not be
over heated or overcooled."
CORRUGATION
ONTI-FLASHOVER POINT
Fig. 5. 31 Insulator construction
Fig. 5. 32 Favorable status of plug
Fig. 5. 33
Overheated plug
Fig.
5.
34 Smoke plug !Wet, left) !Dry, right)
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