|
Spark Plug Condition |
Indications |
|
Normal - correct heat range |
Insulator nose white or very light
tan to rust brown. Little or no cement boil where
the centre electrode protrudes through the insulator
nose. The electrodes are not discoloured or eroded. |
|
Too cold - use hotter plug |
Insulator nose dark grey or black.
Steel plug shell covered with tar-like deposit. |
|
Too hot - use colder plug |
Insulator nose chalky white or may
have satin sheen. Excessive cement boil where centre
electrode protrudes through the insulator nose.
Cement may be white or meringue-like. Centre
electrode may 'blue' and be rounded off at the
edges. Earth electrode may be badly eroded or have a
molten appearance. |
|
Pre-ignition - use a colder plug |
Insulator nose blistered or fused.
Centre plug and remove piston and electrode and side
electrode burned or combustion chamber deposits
melted away. |
|
Detonation - retard timing |
Fractured insulator nose in sustained
and/or richen mixture extreme cases. Insulator nose
covered in tiny beads of aluminium leaving the
piston. Excessive cement boil where centre electrode
protrudes through insulator nose. Specks on plug
shell end. |
