Stihl MS 311, MS 391, MS 191 Service Manual
STIH)
STIHL MS 311, 391
2009-06
Contents
1. Introduction and
Safety Precautions 3
1.1 Introduction 3
1.2 Safety Precautions 4
2. Specifications 5
2.1 Engine 5
2.2 Fuel System 5
2.3 Ignition System 5
2.4 Chain Lubrication 5
2.5 Tightening Torques 6
3. Troubleshooting 8
3.1 Clutch 8
3.2 Chain Drive,
Chain Brake,
Chain Tensioner 9
3.3 Chain Lubrication 10
3.4 Rewind Starter 11
3.5 Ignition System 12
3.6 Carburetor 13
3.7 Engine 16
4. Clutch 17
4.1 Clutch Drum 19
5. Chain Brake 20
6. Engine 27
6.1 Muffler 27
6.2 Leakage Test 28
6.2.1 Preparations 28
6.2.2 Vacuum Test 29
6.2.3 Pressure Test 29
6.3 Oil Seals 30
6.4 Shroud 31
6.5 Cylinder / Crankshaft 32
6.6 Bearings / Crankshaft 35
6.7 Piston 36
6.8 Piston Rings 38
6.9 Decompression Valve 38
7. Ignition System 39
7.1 Ignition Timing 39
7.2 Preseparator 39
7.3 Ignition Module 39
7.4 Testing the
Ignition Module 41
7.5 Spark Plug Boot /
Ignition Lead 42
7.6 Flywheel 43
7.7 Short Circuit Wire 44
7.7.1 Testing 44
7.7.2 Removing and
Installing 44
7.7.3 Ground Wire 46
7.7.4 Contact Spring 46
7.8 Ignition System
Troubleshooting 48
9. Servicing the
AV System 57
9.1 Buffer on Oil Tank 57
9.2 AV Spring on Oil Tank 57
9.3 AV Spring on
Fuel Tank 57
9.4 AV Spring on
Front Handle 58
9.5 Stop Buffer at
Clutch Side 59
9.6 Annular Buffer at
Ignition Side 59
9.7 Handlebar 59
10. Control Levers 61
10.1 Master Control Lever 61
10.2 Throttle Trigger/Interlock
Lever 61
10.2.1 Choke Rod 63
10.2.2 Throttle Rod 64
11. Chain Lubrication 65
11.1 Pickup Body 65
11.2 Oil Suction Hose 65
11.3 Oil Pump 66
11.4 Valve 67
RA_542_00_01_01
5.1 Checking Operation 20
5.2 Brake Band 20
5.3 Brake Lever 22
5.4 Cam Lever 24
5.5 Pins 25
5.6 Chain Tensioner 25
5.7 Bar Mounting Studs 26
8. Rewind Starter 51
8.1 General 51
8.2 Fan housing 51
8.2.1 Segment 51
8.3 Pawls 51
8.4 Rope Rotor 52
8.5 Starter Rope / Grip 53
8.6 Tensioning the
Rewind Spring 54
8.7 Replacing the
Rewind Spring 55
q
© ANDREAS STIHL AG & Co. KG, 2009
1MS 311, MS 391
Contents
12. Fuel System 68
12.1 Air Filter 68
12.2 Baffle 68
12.3 Filter Base 68
12.4 Air Guide Shroud 69
12.5 Carburetor 71
12.5.1 Leakage Test 71
12.6 Servicing the
Carburetor 72
12.6.1 Metering Diaphragm 72
12.6.2 Inlet Needle 73
12.6.3 Pump Diaphragm 74
12.6.4 Air Valve 76
12.6.5 Levers on
Throttle Shaft 76
12.6.6 Adjusting Screws 77
12.7 Carburetor
Adjustment 79
12.7.1 Basic Setting 79
12.7.2 Standard Setting 80
12.8 Carburetor Carrier 81
12.9 Intake Manifold 82
12.10 Tank Vent 83
12.10.1 Testing 83
12.10.2 Removing and
Installing 84
12.11 Fuel Intake 84
12.11.1 Pickup Body 84
12.11.2 Fuel Hose 85
12.11.3 Fuel Suction Hose 86
12.11.4 Tank Housing 87
13. Special Servicing
Tools 88
14. Servicing Aids 90
2 MS 311, MS 391
1. Introduction and Safety Precautions
1.1 Introduction
This service manual contains
detailed descriptions of all the repair
and servicing procedures specific to
this power tool.
You should make use of the
illustrated parts lists while carrying
out repair work. They show the
installed positions of the individual
components and assemblies.
Refer to the latest edition of the
relevant parts list to check the part
numbers of any replacement parts.
A fault on the machine may have
several causes. To help locate the
fault, consult the chapter on
"Troubleshooting" and the
"STIHL Service Training System"
for all assemblies.
Refer to the “Technical Information”
bulletins for engineering changes
which have been introduced since
publication of this service manual.
Technical information bulletins also
supplement the parts list until a
revised edition is issued.
The special tools mentioned in the
descriptions are listed in the chapter
on "Special Servicing Tools" in this
manual. Use the part numbers to
identify the tools in the
"STIHL Special Tools" manual. The
manual lists all special servicing
tools currently available from
STIHL.
Symbols are included in the text and
pictures for greater clarity.
The meanings are as follows:
In the descriptions:
N Action to be taken as shown in
the illustration above the text
– Action to be taken that is not
shown in the illustration above
the text
In the illustrations:
A Pointer
a Direction of movement
@ 4.2 =Reference to another
chapter, i.e. chapter 4.2
in this example.
1
3
2
219RA000 TG
Servicing and repairs are made
considerably easier if the machine
is mounted to assembly stand (3)
5910 890 3100. To do this, secure
the mounting plate (2)
5910 850 1650 to the assembly
stand with two screws (1) and
washers.
The screws must not project since
they, depending on the machine,
may damage housings when the
machine is clamped in position.
The above operation is not
necessary with the new assembly
stand 5910 890 3101 since the
mounting plate is already fitted.
Service manuals and all technical
information bulletins are intended
exclusively for the use of properly
equipped repair shops. They must
not be passed to third parties.
3MS 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.
1.2 Safety Precautions
If the machine is started up in the
course of repairs or maintenance
work, observe all local and countryspecific safety regulations as well
as the safety precautions and
warnings in the instruction manual.
Gasoline is an extremely flammable
216RA000 TG
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.
4 MS 311, MS 391
2. Specifications
2.1 Engine
MS 311 MS 391
Displacement: 59 cm
3
64.1 cm
3
Bore: 47 mm 49 mm
Stroke: 34 mm 34 mm
Engine power to ISO 7293: 3 kW (4 bhp)
at 9,500 rpm
3.2 kW (4.4 bhp)
at 9,500 rpm
Maximum permissible engine speed
with guide bar and chain: 13,000 rpm 13,000 rpm
Idle speed: 2,800 rpm 2,800 rpm
Clutch: Centrifugal clutch without
linings
Centrifugal clutch without
linings
Clutch engages at: 3,500 rpm 3,500 rpm
Engine housing leakage test
at gauge pressure: 0.5 bar
under vacuum: 0.5 bar
2.2 Fuel System
Carburetor leakage test at
0.8 bar
gauge pressure:
Operation of tank vent at
0.5 bar
gauge pressure:
Fuel: as specified in instruction
manual
2.3 Ignition System
2.4 Chain Lubrication
Air gap between ignition
module and fanwheel: 0.20...0.30 mm
Spark plug (resistor type): NGK BPMR 7 A
BOSCH WSR6F
Electrode gap: 0.5 mm
Speed-controlled oil pump with reciprocating piston and
manual flow control
Oil delivery rate:
Ematic oil pump
Oil delivery rate:
Adjustable oil pump
11.5 (+2.5) cm
at 10,000 rpm
6.0 (+/-2.0)...17.5 (+3.0 / -4.5)
3
cm
/min at 10,000 rpm
3
/min
5MS 311, MS 391
2.5 Tightening Torques
DG and P (Plastoform) screws are used in polymer and light metal components. These screws form a
permanent thread when they are installed for the first time. They can be removed and installed as often as
necessary without impairing the strength of the screwed assembly, providing the specified tightening torque is
observed.
For this reason it is essential to use a torque wrench.
Fastener Thread size For component Torque
Remarks
Nm
Screw P 4x14 Chain tensioner cover/engine housing 1.5
Screw P 4x12 Brake band/engine housing 2.0
Collar screw M 10 Collar stud for bar / engine pan 30.0 1)
Collar screw D 8x24 Collar stud for bar / engine housing 16.0
Screw P 5x16 Cover, chain brake / engine housing 4.0
M 10x1 Decompression valve 14.0
Screw P 5x16 Handlebar/plug, AV spring 3.0
Screw P 6x26.5 Handlebar / tank housing, right (polymer) 7.0
Screw P 6x26.5 Handlebar / tank housing, bottom (polymer) 7.0
Screw P 6x25 Hand guard / fan housing 8.0
Screw M 6x30 Shroud / engine housing 10.0
Screw P 6x38 Chain catcher / bearing plug 6.0
Screw P 5x16 Spiked bumper / engine housing 4.0
Screw M 4x12 Manifold/cylinder 4.0 3)
Screw P 6x21.5 Bearing plug / engine housing 6.0
Screw M 5x16 Bearing plug/cylinder 10.0 4)
Screw P 5x20 Fan housing / engine housing 4.0
Screw P 4x12 Air baffle / engine housing 2.0
Carrier M 12x1 LH Carrier / crankshaft 50.0
Screw M 6x25 Engine housing / cylinder, stage 1 4.0 3)
Screw M 6x25 Engine housing / cylinder, stage 2 12.0 3)
Screw D 4x18 Oil pump 4.0 3)
Screw M 5x16 Muffler / cylinder 10.0 1) 3)
Screw M 8x1 Flywheel/crankshaft 33.0 5)
Nut M 5 Carburetor/collar stud 3.5
Screw P 4x14 Pre-separator / engine housing 2.0
Screw P 4x12 Cover plate/fan housing 2.0
Spark plug M 14x1.25 Spark plug 25.0
Screw D 4x18 Ignition module / engine pan 4.0 3)
6 MS 311, MS 391
Remarks:
1) Loctite 242 or 243, medium strength
2) Loctite 648, high strength
3) Screws with antifricton coated binding head
4) Screws with micro-encapsulated binding head
5) Degrease crankshaft/flywheel and mount oil-free
Use the following procedure when refitting a DG or P screw in an existing thread:
Place the screw in the hole and rotate it counterclockwise until it drops down slightly.
Tighten the screw clockwise to the specified torque.
Coat micro-encapsulated screws with medium-strength threadlocking adhesive before re-installing.
This procedure ensures that the screw engages properly in the existing thread and does not form a new thread
and weaken the assembly.
Power screwdriver setting for polymer: DG and P screws max. 500 rpm
Do not use an impact wrench for releasing or tightening screws.
Do not mix up screws with and without binding heads.
7MS 311, MS 391
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