Section 9
Inspection and Reconditioning
9
9.9
Ring failure is usually indicated by excessive oil
consumption and blue exhaust smoke. When rings
fail, oil is allowed to enter the combustion chamber
where it is burned along with the fuel. High oil
consumption can also occur when the piston ring end
gap is incorrect because the ring cannot properly
conform to the cylinder wall under this condition. Oil
control is also lost when ring gaps are not staggered
during installation.
When cylinder temperatures get too high, lacquer
and varnish collect on pistons causing rings to stick,
which results in rapid wear. A worn ring usually
takes on a shiny or bright appearance.
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 after ignition. This creates two flame fronts
which meet and explode to create extreme
hammering pressures on a specific area of the piston.
Detonation generally occurs from using low octane
fuels.
Preignition or ignition of the fuel charge before the
timed spark can cause damage similar to detonation.
Preignition damage is often more severe than
detonation damage. Preignition is caused by a hot
spot in the combustion chamber from sources such as
glowing carbon deposits, blocked cooling fins, an
improperly seated valve, or wrong spark plug(s).
See Figure 9-8 for some common types of piston and
ring damage.
Overheated or Deteriorated Oil
Scored Piston and Rings
Abrasive Scratched Rings
Stuck, Broken Rings
Figure 9-8. Common Types of Piston and Ring Damage.
