Taking Care Of The Guide Bar - Stihl MS 271 Instruction Manual

20 Taking Care of the Guide Bar

19.2 During work
NOTICE
Do not make the mixture leaner to achieve an
apparent increase in power – this could damage
the engine – see "Adjusting the Carburetor".
NOTICE
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).
19.2.1 Check chain tension frequently
A new saw chain must be retensioned more fre‐
quently than one that has been in use already for
an extended period.
19.2.2 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 neces‐
sary – see "Tensioning the Saw Chain".
19.2.3 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 "Ten‐
sioning the Saw Chain".
NOTICE
The chain contracts as it cools down. If it is not
slackened off, it can damage the crankshaft and
bearings.
19.2.4 After a long period of full-throttle oper‐
ation
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 com‐
ponents (ignition, carburetor) from thermal over‐
load.
19.3 After finishing work
► Slacken off the chain if you have retensioned it
at operating temperature during work.
0458-574-0121-D
NOTICE
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.
19.3.1 Short-term storage
Wait for engine to cool down. Keep the machine
with a full tank of fuel in a dry place, well away
from sources of ignition, until you need it again.
19.3.2 Long-term storage
See "Storing the machine"
20 Taking Care of the Guide
Bar
2
► Turn the guide bar over – every time you
sharpen the chain and every time you replace
the chain – this helps avoid one-sided wear,
especially at the nose and underside of the
bar.
► Regularly clean the oil inlet hole (1), the oil‐
way (2) and the bar groove (3)
► Measure the groove depth – with the scale on
the filing gauge (special accessory) – in the
area used most for cutting
Chain type Chain pitch
Picco 1/4" P
Rapid 1/4"
Picco 3/8" P
Rapid 3/8"; 0.325"
Rapid 0.404"
If groove depth is less than specified:
► Replace the guide bar
The drive link tangs will otherwise scrape along
the bottom of the groove – the cutters and tie
straps will not ride on the bar rails.
English
1
3
Minimum
groove
depth
4.0 mm
4.0 mm
5.0 mm
6.0 mm
7.0 mm
29