4 MS 311, MS 391
Engage the bar mounting studs in 
the outer bores in the mounting 
plate and secure the machine in 
position with the nuts (arrows).
Preparations for servicing
Remove the chain sprocket cover, 
saw chain and guide bar before 
carrying out repairs or mounting the 
machine to the assembly stand.
Always use original STIHL 
replacement parts.
They can be identified by the STIHL 
part number, the {  logo 
and the STIHL parts symbol K
This symbol may appear alone on 
small parts.
Storing and disposing 
of oils and fuels
Collect fuel or lubricating oil in a 
clean container and dispose of it 
properly in accordance with local 
environmental regulations.
216RA000 TG
1.2 Safety Precautions
If the machine is started up in the 
course of repairs or maintenance 
work, observe all local and country-
specific safety regulations as well 
as the safety precautions and 
warnings in the instruction manual.
Gasoline is an extremely flammable 
fuel and can be explosive in certain 
conditions.
Always wear suitable protective 
gloves for operations in which 
components are heated for 
assembly or disassembly.
Improper handling may result in 
burns or other serious injuries.
Do not smoke or bring any fire, 
flame or other source of heat near 
the fuel. All work with fuel must be 
performed outdoors only. Spilled 
fuel must be wiped away 
immediately.
Always perform leakage test after 
working on the fuel system and the 
engine.
Always replace damaged parts. 
Check disassembled parts for wear 
or damage before re-installing – 
replace as necessary.
Run the machine only with the 
shroud mounted in position – there 
is otherwise a risk of injury from the 
fanwheel and a risk of engine 
damage due to overheating.
The chapter on tightening torques 
lists all machine components that 
have to be tightened to a specific 
torque or coated with threadlocking 
adhesive. The specifications must 
be maintained when tightening 
down screws, nuts and other 
fasteners in all the procedures 
described in this service manual. 
Fuel system – hose barb 
connectors
Pull off or push on fuel hoses in line 
with the connector, preferably by 
hand, to ensure the tightness of the 
fuel system.
Avoid damaging the hose barb 
– do not use sharp-edged pliers, 
screwdrivers, etc.
Do not cut open fuel hoses with a 
knife or similar tool.
Do not re-use fuel hoses after 
removal. Always install new hoses 
– fuel hoses can be overstretched 
during removal.
Install new fuel hoses either dry or 
with the aid of STIHL press fluid, 
b 14. 
Other press fluids are not approved 
and may result in damage to the fuel 
hoses.
Coat the ends of the hoses and the 
connectors with STIHL press fluid 
and then push the new hoses on to 
the hose barbs, b 14.