Piston Scoring Caused By Heavy Carbon Deposits; Piston Damage Caused By A Too High Engine Speed; Piston Ring Breakage - Husqvarna 525L Workshop Manual

Piston scoring caused by heavy carbon
deposits
Too heavy carbon depositing can cause damage
similar to that caused by insufficient lubrication.
However, the piston skirt has a darker colour
caused by the hot combustion gases that are
blown past the piston.
This type of piston damage starts at the exhaust
port where carbon deposits can become loose and
get trapped between the piston and the cylinder
wall.
Typical for this type of piston damage is brown or
black discoloration of the piston skirt.
Cause:
Wrong type of two-
stroke oil or petrol.
Incorrect oil mixture in
the petrol.
Incorrect carburettor
setting.
Piston damage caused by a too high
engine speed.
Typical damage associated with a too high engine
speed includes broken piston rings, broken circlip
on the piston 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 temperature. 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 piston 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.
Action:
Change the fuel.
Change to a fuel with
the correct oil mixture.
Correct the carburettor
setting
Repair instructions
49
English -