Piston Wear - Husqvarna K770 Workshop Manual

6.8.7 Piston wear tolerances
6.8.7.1 Piston ring play
If the piston ring play is more than .006 in/0.15 mm, the
piston ring groove must be measured as set out below.
6.8.7.2 Piston ring groove
If the piston ring groove is larger than .06 in/1.6 mm, the
piston must be replaced. Install a complete piston kit
with piston rings, needle bearing and wrist pin.
6.8.7.3 Piston ring wear
Put the piston ring in the cylinder with the aid of the
piston. Put it around 1 in/2.5 cm from the bottom of the
cylinder. The piston ring distance (1) must be max. .04
in/1.0 mm.
44 - Repair and servicing
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1
1

6.9 Piston wear

The cause of engine failure can be hard to find if the
previous operation and service of the product is not
available. Use the following examples for help.
6.9.1 Usual wear
Usual wear is easiest to see on the piston sections that
point at the exhaust and inlet sides. The picture shows
that the piston has been polished to give a bright
surface. The lines from the production can also be seen.
Oil on the piston rings shows correct lubrication. The
piston rings can move freely in the piston ring groove.
6.9.2 Dust
If dust enters the engine, the engine life decreases. The
effect of dust can be seen with a magnifying glass.
Rounded lines in line with the travel of the piston are
clear signs. The lines after production cannot be seen.
The surface is matt.
The usual cause is a bad filter and/or leakage. Examine
the condition of the filters and gaskets. Also examine the
rubber guides between the cylinder, the carburetor and
the connections. Look for dust from the filter units to the
inlet by the cylinder. Carbon particles on the top of the
piston show that the product is used at short intervals.
The engine has not become fully warm.
651 - 001 - 27.06.2018