8
2,,1,,2
Chain Brake
The chain brake is a
spring-loaded
band brake without linings" Its main
components are the brake band,
tension spring, handguard and re-
lease plate - which operates the
isolating clutch"
The chain brake is actuated by
means of the handguard which can
be used to release and engage the
brake"
2.2
Troubleshooting Chart
Fault
Saw chain turns at idle speed
The chain brake is
released (reset)
by pulling the handguard back
against the handlebar"
This
move-
ment is transmitted
via
a lever
system which preloads the tension
spring and
disengages
the brake
band. At the same time the release
plate moves back and
allows the
driving plate to engage in the teeth
of the hub"
The
brake lever, which is
connected to the tension spring,
brake band and release plate, is
locked in the idle position by the
relay lever.
Cause
Engine idle speed too high
Clutch spring stretched or fatigued,
spring hooks broken
Excessive chain
sprocket
wear
Incorrect chain tension
Chain stops in
mid-cut
even with Isolating clutch worn
engine at maximum speed -
Isolating clutch
disengages
Flat spring broken
during cutting
Isolating clutch does not re-engage Engine idle speed too high
after releasing chain brake
Flat spring broken
Saw chain does not stop
imme-
Tension spring broken
diately when chain brake is engaged
The chain brake is actuated by
mo-
ving the handguard
towards
the
bar
nose" This movement unlatches
the
brake lever and causes
the
brake
band to be clamped around
the
clutch drum by the force
of
the
pre-
loaded brake spring" The release
plate simultaneously
disengages
the driving plate from the hub and
interrupts the flow of power between
the crankshaft and the centrifugal
clutch"
Clutch drum and
saw
chain
are brought to a
standstill within a
fraction of a second even if the
en-
gine continues running at high
speed"
Remedy
Readjust at idle speed
adjustment
screw
Renew clutch spring
Tension saw chain properly
Renew hub and driving plate
Renew flat spring
Readjust at idle speed adjustment
screw
Renew flat spring
Renew tension spring
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