Spark Plugs
Chapter 2
Study Tips
The spark plugs are critical parts that dominate
the engine combustion and bear a major
responsibility for higher engine performance.
Spark Plugs
Chapter 2 Spark Plugs
33
[Appearance] The insulator nose section
is scorched extremely white with small
black deposits. Rapid electrode wear.
[Result] 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.
Overheating
1
[Appearance] The center electrode or ground
electrode is melted or scorched. There are
spots on the insulator nose section and
deposits of aluminum or other metal powder.
[Result] 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.
Pre-ignition
2
[Appearance] The insulator nose section
is cracked or broken.
[Results] Misfiring
[Cause] Severely abnormal combustion,
lack of attention to gap adjustment.
Insulator breakage
3
[Appearance] Thread screw section melting.
[Result] Power loss due to engine damage.
[Cause] Incorrect spark plug tightening.
Housing installation screw
section melting
4
[Appearance] The electrode is bent and
the insulator nose 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.
Physical damage to ignition
tip section
5
[Cause] Overheating of the ground
electrode and severe engine vibration.
Ground electrode breakage
6
1
2
3
4
5
6
Содержание CAFITESSE 300
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