Husqvarna 243RJ Workshop Manual page 47

Exhaust side damaged by a broken piston
ring. The piston ring parts damage the top
section and cause score marks.
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.
Cylinder and piston
Piston damage caused by a too high engine speed.
Typical damage from too high engine speed is ruptured piston ring/piston rings, broken
circlip on the gudgeon pin, faulty bearings or that the guide pin for the piston ring has
become loose.
Piston ring breakage
A too "lean" carburettor setting results in a too high speed and a high piston tempera-
ture. If the piston temperature rises above the normal working temperature the piston
ring can seize in its groove, consequently it will not sit deep enough in its groove. The
edges of the piston ring can then hit the top edge of the exhaust port and be smashed
and also cause piston damage.
A too high engine speed can also cause rapid wear to the piston ring and play in the pis-
ton ring groove primarily in front of the exhaust port. The ring is weakened by the wear
and can be caught in the port causing serious piston damage.
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.
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 overheating. 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
between 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.
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