Husqvarna K1270 Workshop Manual page 56

Cylinder/Piston
SCORING, LACK OF OIL
Damage of this type is always the result of over-
heating. The cores are usually on the exhaust side,
which is the hottest. Inlet side can show similar
damage. Check whether the machine has broken
down due to an incorrect oil mixture, or no oil at
all. The oil on the overheated piston has probably
carbonized. Check instead whether the connecting
rod or the crankcase has a film of oil.
If a lack of oil can be excluded, inlet leakage
should be looked at. When the engine has air
leakage on the inlet side, this results in a lean fuel/
air mixture which first and foremost give scoring on
the exhaust side. Look for combination effect as in
the example below.
OVERHEATED PISTON TOP
Clear signs of overheating are aluminium deposits
on the top of the piston, which in extreme cases
can result in melting. Excess air in relation to
the fuel volume increases the temperature in the
combustion chamber. Therefore check whether
the inlet system is blocked. Check that the fuel
supply has not been obstructed due to a defective
fuel hose, tank vent or the pulse hose. Fuel with a
too low octane grade cause ignition at the wrong
point like spark plugs with the wrong thermal
rating, which both increase the temperature in the
combustion chamber.
Check that the flywheel's key on the crankshaft is
intact, as the flywheel position on the crankshaft
controls the ignition time point.
ASSEMBLY
Oil in
New or cleaned bearings and piston rings should
be oiled in with 2-stroke oil before assembly to
initially ensure satisfactory lubrication.
The arrow pointing towards the exhaust port
The piston is not symmetrical.
NOTE! It is important that the arrow is turned
towards the muffler when assembling the piston
on the connecting rod.
Fit the needle bearing in the connecting rod. Fit
a circlip in the piston, hold the piston in position,
press in the gudgeon pin and fit the other circlip.
Check that the circlips are seated correctly in their
grooves.
56
- English
PISTON DAMAGE - SCORING
PISTON DAMAGE - OVERHEATED PISTON TOP
16-1
ARROWS INDICATE THE DIRECTION
16-1