Originally posted by Kennard:
Originally posted by Rogerm60:
"or leakage which drains energy causing a spark somewhere besides the plug's tip. As most books will tell you, shattered plug insulators are usually caused by detonation. Crossfire between leaky plug wires can cause occasional detonation. Detonation causes drastically increased pressures within the cylinder and can damage plug tips and ceramic insulators.



OK, so my question is, how DOES detonation break an insulator ? The insulator is not inside the combustion chamber. Can detonation be forceful enough to travel way up inside the plug and crack the ceramic from the inside ? Is the ceramic that insulates the tip part of the exterior ceramic ? It would seem to me that if there was sufficient catastrophe to the plug tip inside the combustion chamber that the force would destroy the tip long before it could crack the insulator outside. It seems as if the tip looked untouched that it would be extremely unlikely that the ceramic could be broken on the outside. Please esplain yourself Lucy, and thanks for all the input so far, it has been very interesting and informative.





Detonation does not break the external portion of the insulator.

Detonation can break the inner portion of the insulator, the cone, that is exposed to the combustion chamber.

The external part of the insulator is broken by mechanical damage, usually during installation.

Sometimes (but very rare) a poorly made spark plug may blow apart so that the ceramic portion slips out of the matal shell. In my experience, this was more common with Champion plugs, but I have seen it on others. Although extreme cylinder pressure (including spikes in pressure from detonation) can contribute to this, it is mostly a problem with building the plug.

Jim Johnson 98 SVT 03 Escape Limited