Kohler K9J Service Manual page 112

takes on a shiny or bright appearance. Scratches
on rings and piston are caused by abrasive mate-
rial 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 fuels with too low of an octane rating.
Pre-ignition or ignition of the fuel charge before
the timed spark can cause damage similar to
detonation. Pre-ignition damage is often more se-
vere than detonation damage - often, a hole is
quickly burned right through the piston dome. Pre-
ignition is caused by a hot spot in the combustion
chamber from sources such as: glowing carbon
Stuck, Broken Rings
Abrasive Scratched Rings
deposits, blocked fins, improperly seated valves or
wrong spark park plug.
See Figure 11-1 0 for some common types of pis-
ton and ring damage.
Service
K-Series service replacement pistons are available
in STD bore size, and in .003", .010", .020", and
.030" oversizes. Replacement pistons include new
piston ring sets and new piston pins.
Service replacement piston ring sets are also
available separately for STD/.003" (same ring set
for both sizes), .010", .020" and .030" oversized
pistons. Always use new piston rings when install-
ing pistons. Never reuse old rings.
The cylinder bore must be deglazed before service
ring sets are used.
Abrasive Worn Rings
Scored Piston and Rings
Figure 11-10. Common Types Of Piston And Ring Damage.
11.9
m