Stihl MS 391 Safety Manual

MS 311, MS 391
English
25
N Press the button on the
decompression valve
N Restart the engine
During the break-in period
A factory new machine should not be run
at high revs (full throttle off load) for the
first three tank fillings. This avoids
unnecessarily high loads during the
break-in period. As all moving parts
have to bed in during the break-in
period, the frictional resistances in the
shortblock are greater during this period.
The engine develops its maximum
power after about 5 to 15 tank fillings.
During work
Check chain tension frequently
A new saw chain must be retensioned
more frequently than one that has been
in use already for an extended period.
Chain cold
Tension is correct when the chain fits
snugly against the underside of the bar
but can still be pulled along the bar by
hand. Retension if necessary – see
"Tensioning the Saw Chain".
Chain at operating temperature
The chain stretches and begins to sag.
The drive links must not come out of the
bar groove on the underside of the bar –
the chain may otherwise jump off the
bar. Retension the chain – see
"Tensioning the Saw Chain".
After a long period of full-throttle
operation
After a long period of full-throttle
operation, allow engine to run for a while
at idle speed so that the heat in the
engine can be dissipated by flow of
cooling air. This protects engine-
mounted components (ignition,
carburetor) from thermal overload.
After finishing work
N Slacken off the chain if you have
retensioned it at operating
temperature during work.
Operating Instructions
Do not make the mixture leaner to
achieve an apparent increase in
power – this could damage the
engine – see "Adjusting the
Carburetor".
Open the throttle only when the
chain brake is off. Running the
engine at high revs with the chain
brake engaged (chain locked) will
quickly damage the shortblock
and chain drive (clutch, chain
brake).
The chain contracts as it cools
down. If it is not slackened off, it
can damage the crankshaft and
bearings.
Always slacken off the chain again
after finishing work. The chain
contracts as it cools down. If it is
not slackened off, it can damage
the crankshaft and bearings.

Stihl MS 391 Specifications

General

Motor type	2-stroke motor
Chain gauge	1.6 mm
Chain pitch	3/8 \
Automatic oiling	Yes
Oil tank capacity	0.35 L
Fuel tank capacity	0.6 L
Engine displacement	64.1 cm³
Engine power	4.4 hp
Power source	Gasoline

Weight and Dimensions

Weight	6200 g