Chain Brake; Checking Operation; Brake Band; Handlebar - Stihl MS 311 Service Manual

5.

Chain Brake

5.1

Checking Operation

The chain brake is one of the most
important safety devices on the
machine. 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.
– Starting 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 (less
than a second) is imperceptible to
the eye.
If the chain brake does not operate
properly, refer to troubleshooting,
b 3.2.
20
5.2

Brake Band

– Remove the clutch drum, b 4.1
– Troubleshooting, b 3.2
1
: Pull off the bumper strip (1).
1
: Take out the screws (arrows).
– Remove the cover (1).
1
– Engage the chain brake.
The brake band is now tensioned.
: Remove the screw (1) from the
underside of the machine.
: Pry the brake band (1) out of its
seat (arrow).
– Remove the brake band (1).
Do not overstretch the brake band.
– Pull the hand guard towards the
handlebar to simplify assembly of
the brake band.
MS 311, MS 391
1