Chevrolet Light Duty Truck 1973, Service Manual

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E N G IN E ELECTRICAL 6 Y -4 9
DETONATION
Overadvanced ignition timing, or the use of low octane fuel will result in detona­
tion commonly referred to as engine knock.
This causes severe shock inside the combustion chamber resulting in damage to
the adjacent parts which include spark plugs. A common result of detonation is to
have the sidewire of a spark plug torn off.
INSTALL A NEW PLUG OF THE RECOMMENDED HEAT RANGE AFTER
PROBLEM HAS BEEN CORRECTED.
Detonation
INSUFFICIENT INSTALLATION TORQUE
Failure to install a spark plug with sufficient torque results in poor contact
between the spark plug and the engine seat. The lack of proper heat transfer,
resulting from poor seat contact, causes excessive overheating of the spark plug and,
in many cases, severe damage as shown.
A NEW SPARK PLUG OF THE RECOMMENDED HEAT RANGE SHOULD BE
INSTALLED IN ACCORDANCE WITH AC INSTALLATION INSTRUCTIONS.
In su fficie n t
Installation Torque
P R E -IG N ITIO N
Pre-ignition, causing burned or blistered insulator tip and badly eroded elec­
trodes, indicates excessive overheating. Cooling system stoppages or sticking valves
can also result in pre-ignition. Lean fuel-air mixtures are an additional cause.
INSTALL A NEW PLUG OF THE RECOMMENDED HEAT RANGE AFTER
PROBLEM HAS BEEN CORRECTED.
Sustained high speed, heavy load service can produce high temperatures which
will cause pre-ignition and, in this instance a colder spark plug should be used.
Pre-ignition
IMPROPER INSTALLATION
Dirty threads in an engine head will result in the plug seizing before it is actually
seated. This results in poor heat transfer and causes the spark plug to overheat.
To insure proper seating of a new spark plug in the head, dirty cylinder head
threads should be cleaned with a greased thread chaser of the proper size.
ELIMINATE THE CAUSE AND INSTALL A NEW PLUG OF THE RECOM­
MENDED HEAT RANGE.
Improper Installation
LIGHT DUTY TRUCK SERVICE MANUAL