Husqvarna 129C Workshop Manual page 48

Repair Instructions
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.
Cause:
• Faulty air filter. Small dust particles pass
through the filter.
• The filter is worn out due to too much cleaning,
whereby small holes have appeared in the
material.
• Unsuitable filter maintenance, such as wrong
method or wrong cleaning agent. Flock material
becomes loose and holes appear.
• Air filter incorrectly fitted.
• Air filter damaged or missing.
Larger, softer particles that penetrate into the
engine cause damage to the piston skirt under the
piston ring as the illustration shows.
Cause:
• Air filter incorrectly fitted.
• Air filter damaged or missing.
Larger, harder particles that enter the engine cause
serious damage to the underside of the piston skirt.
Cause:
• Air filter damaged or missing.
• Parts from the carburettor or intake system have
come loose and entered the engine.
48
- English
Small score marks and a matt, grey
surface on the piston's inlet side
caused by fine dust particles.
Inlet side.
Particles of dust and dirt from carbon-like
deposits on the top of the piston and in the
piston ring groove. The piston ring sits firmly
in the groove. Piston material has been worn
away.
The lower part of the piston skirt is thinner
on the inlet side than on the exhaust side.
The piston scored and worn from the
piston ring down on the inlet side.
Extensive damage to the lower part of the
piston's inlet side.