Husqvarna 345FR, Workshop Manual

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49
Cylinder and piston
Service tips
Wear tolerances
When the surface coating is worn
and aluminium appears. Max. 1.0 mm with the piston ring
inserted in the lower part of the
cylinder. Max. 1.6 mm. Clean the groove be-
fore checking the measurement. Max. 0.15 mm. Clean the groove
before checking the measure-
ment.
Piston ring play Piston ring groove Piston ring gap
Cylinder bore
Defect:
Broken cooling
fi
ns, damaged threads or sheared bolts by
the exhaust port.
Seizure marks in the cylinder bore (especially by the ex-
haust 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
fi
ne 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
fi
ne
fi
le of
fi
ne
grade emery cloth. Before the piston is re
fi
tted 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 re
fi
tting. 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.