Husqvarna K1270 Workshop Manual page 55

PISTON RINGS
Piston ring wear can be measured by inserting
the piston ring into the cylinder and measuring the
piston ring gap using feeler gauges. The piston ring
gap may be max. .04 in./ 1.0 mm.
Use the piston to press in the piston ring exactly
flat, about one inch/a few centimetres from the
base of the cylinder.
PISTON DAMAGE
The cause of engine failure is often difficult to
establish, primarily when the machine's history is
not known. The typical cases below can provide
some guidance. (Pistons from Husqvarna K1260.)
NORMAL WEAR
Typical normal wear is easiest to see on the piston
sections that face the exhaust and inlet sides. From
the detailed image it is evident that the piston has
been "polished" to give a bright surface, yet the
machining lines after manufacture are still visible.
Oiled piston rings indicate correct lubrication. The
piston rings have full moveability in the piston ring
groove.
DUST
Dust entering the engine will dramatically shorten
its life. The effect of dust can be clearly seen if
the piston is studied under a magnifying glass.
Spiral lines in line with the piston's travel are a
clear sign. The machining lines after manufacture
cannot be seen. The surface is matt. Usual cause
is inadequate filter service and/or leakage. Check
the condition of the filters and gaskets. Also check
the rubber guides between the cylinder and the
carburettor as well as the connections. Methodical
searching for dust, from the filter units to the inlet
by the cylinder, should give a result. (The sooty
piston top indicates that the machine works at
short intervals and has not been run completely
warm.)
WEAR TOLERANCES - PISTON RINGS
PISTON DAMAGE - NORMAL WEAR
PISTON DAMAGE - DUST
Cylinder/Piston
.04 in.
1.0 mm
English -
55