Kohler COMMAND CH18-745 User Manual download pdf (Page 180)

10.9

Section 10

Inspection and Reconditioning

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 10-8 for some common types of piston and

ring damage.

Overheated or Deteriorated Oil

Scored Piston and Rings

Abrasive Scratched RingsStuck, Broken Rings

Figure 10-8. Common Types of Piston Damage.

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Kohler COMMAND CH18-745 User Manual Page 180