Chain Brake; Checking Operation; Brake Band - Stihl MS 661 Manual

5.

Chain Brake

5.1

Checking Operation

The chain brake is one of the most
important safety devices on the
chain saw. Its efficiency is
measured in terms of the chain
braking time, i.e. the time that
elapses between activating the
brake and the saw chain coming to
a complete standstill.
Contamination (with chain oil,
chips, fine particles of abrasion,
etc.) and smoothing of the friction
surfaces of the brake band and
clutch drum impair the coefficient of
friction, which prolongs the braking
time. A fatigued or stretched brake
spring has the same negative effect.
– Start the engine.
– With the chain brake
activated (locked), open the
throttle wide for a brief
period (max. 3 seconds) – the
chain must not rotate.
– With the chain brake released,
open the throttle wide and
activate the brake manually – the
chain must come to an abrupt
stop.
The braking time is in order if
deceleration of the saw chain is
imperceptible to the eye (a fraction
of a second).
If the chain brake does not operate
properly, refer to troubleshooting,
b 3.2.
MS 661, MS 661 C-M
5.2

Brake Band

– Troubleshooting, b 3.2
– Remove the clutch drum,
– Remove the clutch, b 4.2
– Take out the screw and remove
the side plate.
1
1
: Take out the screws (1) and
remove the cover (2).
1
– Engage the chain brake
– Brake band no longer
tensioned in its seat.
: Take out the screw (1) and pry
the brake band (2) out if its seat
(arrow).
Do not overstretch the brake band.
– Disengage the chain brake.
1
: Turn the brake band (1) to one
side and disconnect it from the
brake lever (2).
1
Install a new brake band if there are
noticeable signs of wear (large
2
areas on inside diameter and/or
parts of outside diameter – arrows)
and its remaining thickness is less
than 0.6 mm.
Installing
1
2
The chain brake must be
disengaged.
: Hold the brake band (1)
sideways, attach it to the brake
lever (2) and then swing it in the
direction of its seat.
2
2
19