Kohler MAGNUM M18

SECTION 10
INSPECTION AND RECONDITIONING
Inspection
Scuffing and scoring of pistons and cylinder walls oc-
curs when intemal temperatures approach the welding
point of the piston. Temperatures high enough to do
this are created by friction, which is usually attributed
to improper lubrication, and/or overheating of the
engine,
Normally, very little wear takes place in the piston
boss-piston pin area. If the original piston and con-
necting rod can be reused after new rings are in-
stalled, the original pin can also be reused but new
piston pin retainers are required. The piston pin is
included as part of the piston assembly--if the pin
boss in piston, or the pin are wom or damaged, a new
piston assembly is required.
Ring failure is usually indicated by excessive oil con-
sumption and blue exhaust smoke. When rings fail,
oil is allowed to enter the combustion chamber where
it is bumed along with the fuel. High oi! consumption
can also occur when the piston ring end gap is incor-
rect 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.
10.10
When cylinder temperatures get too high, lacquer and
vamish collect on pistons causing rings to stick which
results in rapid wear. A wor ring usually takes on a
shiny or bright appearance. Scratches on rings and
pistons are caused by abrasive material such as car-
bon, 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 detona-
tion damage. Preignition is caused by a hot spot in
the combustion chamber from sources such as: glow-
ing carbon deposits, blocked fins, improperly seated
valves, or wrong spark plugs.
See Figure 10-12 for some common types of piston
and ring damage.