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6
Cylinder and piston
Small score marks and a matt, grey surface
on the piston’s inlet side caused by fine
dust particles.
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.
Action:
Fit a finer grade filter.
Check the filter carefully for holes and
damage after cleaning. Replace the
filter if necessary.
Clean more carefully and use the right
cleaning agent (such as tepid soapy
water).
Change the filter.
Fit the filter correctly.
Fit a new air filter.
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.
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.
Action:
Fit the air filter correctly.
Fit a new air filter.
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.
The piston scored and worn from the piston
ring down on the inlet side.