Husqvarna 125C Workshop Manual page 43

6
Cylinder, piston, crankshaft, crankcase
The guide pin for the piston ring has been
pushed up through the top of piston.
Piston ring guide pin
vibrated loose
A too high engine speed can cause the
ends of the piston ring to hammer against
the guide pin when the piston ring moves
in its groove. The intensive hammering
can drive out the pin through the top of
the piston causing serious damage also
to the cylinder.
Small score marks and a matt, grey surface
on the piston's inlet side caused by fine
dust particles.
42
Deep, irregular grooves caused by a loose
circlip. Shown here on the piston's inlet
side.
Damage caused by
gudgeon pin circlips
A too high engine speed can cause the
gudgeon pin circlips to vibrate. The
circlips are drawn out of their grooves due
to the vibrations, which in turn reduces
the circlips' tensioning power. The rings
can then become loose and damage the
piston.
Foreign objects
Everything other than clean air and pure fuel that enters the engine's inlet port
causes some type of abnormal wear or damage to the cylinder and piston.
This type of increased wear shows on the piston's inlet side starting at the lower
edge of the piston skirt.
The damage is caused by badly filtered air that passes through the carburettor and
into the engine.
Irregular grooves on the piston's inlet side
caused by a broken roller retainer.
Bearing failure
Failure of the crankshaft bearing or on the
connecting rod bearing is usually caused
by a too high engine speed, resulting in
the bearing being overloaded or overheat-
ing. This in turn can cause the bearing
rollers or ball to glide instead of rotate,
which can cause the roller or ball retainer
to break.
The broken debris can be trapped be-
tween the piston and cylinder wall,
damaging the piston skirt.
Debris can also pass up through the
cylinder's transfer channels and cause
damage to the top and sides of the piston
as well as to the cylinder's combustion
chamber.