Husqvarna 324HDA, Workshop Manual

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34
6
Cylinder block and valve mechanism
502 50 18-01
A B
The cylinder and the piston are two of the components exposed to most strain in the engine. They must withstand,
for example, high speeds, large temperature swings and high pressure. Moreover, they must be resistant to wear.
Despite these tough working conditions, major piston and cylinder failure is relatively uncommon. The reasons for
this include new coatings in the cylinder bore, new types of oil and grease and refined manufacturing techniques.
When servicing these components, cleanliness is of the utmost importance.
Before dismantling or other actions are performed on the cylinder block and valve mechanism it is recommended
that a compression test is made to easily determine whether any faults exist, for example, leaking valves, leaking
valve guides, damaged piston rings or a damaged piston.
Compression test
Empty the fuel tank and fit a
compression gauge.
Ensure that the choke valve is open
and that the throttle is fully open.
Turn over the engine with the starter.
Compression test
Empty the fuel tank and fit a
compression gauge in the spark plug
hole.
Set the choke in the open position and
the throttle at full throttle.
Turn over the engine powerfully with
the starter (approximately 2000 rpm).
Read the compression gauge.
Repeat the test procedure a number of
times and calculate an average value
for the readings.
On a fully functional engine the compression pressure should be 0.9 – 1.1
kPa (131 –159 psi)
Check the valve play
Dismantle the spark plug, air filter
cowling, cylinder cover and valve cover.
Check the valve play
The valve clearance should be checked
when the engine is cold.
1. Dismantle the spark plug, the air
filter cowling and cylinder cover.
2. Remove the ventilation hose (A)
from the valve cover.
3. Remove the screws (B) holding the
valve cover and lift off the cover.
Turn over the engine until the marking
(A) on the timing gear points straight
up. 4. Turn over the engine until the
marking (A) on the timing gear
points straight up. That’s to say, the
valves are closed and the rate of
expansion starts.