10.10
Section 10
Inspection and Reconditioning
Scratches on rings and pistons are caused by abrasive
material such as carbon, dirt, or pieces of hard metal.
Detonation damage occurs when a portion of the fuel
charge ignites spontaneously from heat and pressure
shortly a er ignition. This creates two fl ame fronts,
which meet and explode to create extreme hammering
pressures on a specifi c area of the piston. Detonation
generally occurs from using low octane fuels.
Pre-ignition, or ignition of the fuel charge before the
timed spark can cause damage similar to detonation.
Pre-ignition damage is o en more severe than
detonation damage. Pre-ignition is caused by a hot
spot in the combustion chamber such as glowing
carbon deposits, blocked cooling fi ns, an improperly
seated valve, or wrong spark plug(s).
See Figure 10-12 for some common types of piston
and ring damage.
Overheated or Deteriorated Oil
Scored Piston and Rings
Abrasive Scratched Rings
Stuck, Broken Rings
Figure 10-12. Common Types of Piston Damage.
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