Husqvarna 343F, Workshop Manual

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49
6
Cylinder and piston
Cause:
• Air filter damaged or missing.
• Parts from the carburettor or intake
system have come loose and
entered the engine.
Action:
Fit a new air filter.
Regular service and inspection.
Extensive damage to the lower part of the
piston’s inlet side.
Service tips
Defect:
Broken cooling fins, damaged threads or sheared bolts by
the exhaust port.
Seizure marks in the cylinder bore (especially by the
exhaust port).
Surface coating in the cylinder bore worn out (primarily at
the top of the cylinder).
The piston shows signs of seizure score marks.
Piston ring burnt in its groove.
Bolts much too tight in the aluminium material.
Action:
In severe cases – replace the cylinder.
Repair the threads using Heli-Coil.
Polish the damaged area using a fine grade emery cloth
so that the coating of aluminium disappears.
With deep seizure score marks the piston and cylinder
should be replaced.
Replace the cylinder and piston.
Carefully polish the damaged area using a fine file of fine
grade emery cloth. Before the piston is refitted the cylinder
should be polished as above. With deep score marks the
piston and cylinder should be replaced.
Carefully loosen the piston rings and clean the groove well
before refitting. Carbon deposits in the groove impair the
important heat transfer between the piston and cylinder.
NOTE!
Be careful with the lower edge of the piston ring
groove. If this is damaged, or if carbon deposits
remain, the compression pressure can leak through.
Check the wear on the piston ring by placing it in the lower
part of the cylinder.
Position a suitable punch on the bolt head and give a few
sharp knocks with a hammer. If the bolt still does not loosen,
repeat the procedure.
Larger, harder particles that enter the engine cause serious damage to the under-
side of the piston skirt.