Kohler Command Pro CV980 - Manual (Page 101)

Section 9
Inspection and Reconditioning
9
9.9
Overheated or Deteriorated Oil Scored Piston and Rings
Abrasive Scratched Rings Stuck, Broken Rings
Ring failure is usually indicated by excessive oil
consumption and blue exhaust smoke. When rings
fail, oil is allowed to enter the combustion chamber
‘Ž›Žȱ’ȱ’œȱ‹ž›—ŽȱŠ•˜—ȱ ’‘ȱ‘ŽȱžŽ•ǯȱ’‘ȱ˜’•ȱ
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
œ‘˜›•¢ȱŠĞŽ›ȱ’—’’˜—ǯȱ‘’œȱŒ›ŽŠŽœȱ ˜ȱ̊–Žȱ›˜—œȱ
which meet and explode to create extreme hammering
™›Žœœž›Žœȱ˜—ȱŠȱœ™ŽŒ’ęŒȱŠ›ŽŠȱ˜ȱ‘Žȱ™’œ˜—ǯȱŽ˜—Š’˜—ȱ
generally occurs from using low octane fuels.
Preignition or ignition of the fuel charge before the
timed spark can cause damage similar to detonation.
›Ž’—’’˜—ȱŠ–ŠŽȱ’œȱ˜ĞŽ—ȱ–˜›ŽȱœŽŸŽ›Žȱ‘Š—ȱ
detonation damage. Preignition is caused by a hot
spot in the combustion chamber from sources such
Šœȱ•˜ ’—ȱŒŠ›‹˜—ȱŽ™˜œ’œǰȱ‹•˜Œ”ŽȱŒ˜˜•’—ȱꗜǰȱŠ—ȱ
improperly seated valve, or wrong spark plug(s).
ŽŽȱ’ž›ŽȱşȬŞȱ˜›ȱœ˜–ŽȱŒ˜––˜—ȱ¢™Žœȱ˜ȱ™’œ˜—ȱŠ—ȱ
ring damage.
Figure 9-8. Common Types of Piston Damage.