Kohler COMMAND CV11-16 Service Manual page 121

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. 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 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.
Stuck, Broken Rings
Overheated or Deteriorated Oil
Figure 10-7. Common Types of Piston and Ring Damage.
Inspection and Reconditioning
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 fi ns, improperly
seated valve, or wrong spark plug. See Figure 10-7 for
some common types of piston and ring damage.
Replacement pistons are available in STD bore size,
and in 0.08 mm (0.003 in.), 0.25 mm (0.010 in.), and
0.50 mm (0.020 in.) oversizes. Replacement pistons
include new piston ring sets and new piston pins.
Service replacement piston ring sets are also available
separately for STD, 0.25 mm (0.010 in.), and 0.50
mm (0.020 in.) oversized pistons. The 0.08 mm
(0.003 in.) oversize piston uses a STD ring set.
Always use new piston rings when installing pistons.
Never reuse old rings.
The cylinder bore must be deglazed before service
ring sets are used.
Abrasive Scratched Rings
Scored Piston and Rings
Section 10
10
10.9