Technical Information · issue 27 of 2009
New chain saws STIHL MS 311, MS 391
IssueTI 27/2009
Engine family 1140
Full text
Page 1 of 8
STIH)
Technical Information 27.2009
New chain saws STIHL MS 311, MS 391 – Series 1140
Contents
1. Technical description
2. Specifications
3. Special tool and service accessories
4. Servicing
TI_27_2009_30_01_01.fm englisch / English
)m~ge 2 Technical Information 27.2009
The new, robust STIHL MS 311 and STIHL MS 391 1.2 Air filter system with pre-separator
chain saws are now ready for use by farmers,
landscapers and tradespeople.
With an innovative reduced emissions engine
concept and pre-separation air filter system, they
are especially powerful, economical, clean and low-
maintenance.
Characteristic features of the powerful new STIHL
MS 311 and MS 391:
– Reduced exhaust emissions
– High performance
– High torque over a wide range of engine speeds
– Substantially lower fuel consumption –
depending on type of use up to 20 % compared
with conventional 2-stroke engines
0001TI002 KN
– Extended filter life – twice the service life of the
previous model
The redesigned anti-vibration system ensures a low The intake air is swirled and diverted horizontally by
vibration level. the ramp in front of the ignition module. The larger
and heavier particles carried in the air (black arrows)
The air filter system with pre-separator extends filter are expelled upward and outward.
cleaning intervals substantially. Via the pre-separator duct, the pre-cleaned air (gray
The ignition system with electronic adjustment of the arrows) is fed to the air filter.
ignition timing permits optimum performance and The air filter system can be adapted to different
lower exhaust emissions. operating conditions by the insertion of different air
The chain saws are equipped with a decompression filters. Installation is simple.
valve for easy starting.
1.2.1 Felt filter
For normal, dry or very dusty operating
environments.
1. Technical description
1.2.2 Mesh filter
1.1 How stratified scavenging works –
For extreme winter conditions (e.g., powdered or
An air cushion (air without fuel) separates fresh
drifting snow or frost formation).
mixture and exhaust. The air cushion is placed in
front of the fresh fuel/oil mixture. At the beginning of
the "exhaust and transfer" stroke, air without fuel
streams out of the transfer ports into the combustion
chamber and flushes the exhaust into the exhaust
port. The fresh air cushion prevents the
subsequently in-rushing fuel mixture from flowing
into the exhaust port. This results in reduced
exhaust emissions and lower fuel consumption.
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Technical Information 27.2009 Page 3
1.3 Shroud 1.5 Filler cap
The new tank cap with clip can be opened and
closed quickly and easily:
Simple and dirt-free fill up of the machine provided
by large, easily-accessible tank openings.
2. Specifications
2.1 Engine
STIHL single cylinder two-stroke engine
MS 311 MS 391
Displacement 3.60 cu. in. 3.90 cu. in.
(59 cm3) (64.1 cm3)
Cylinder bore 1.85 in. 1.93 in.
(47 mm) (49 mm)
Piston stroke 1.34 in. 1.34 in.
(34 mm) (34 mm)
Power output 4.2 bhp 4.4 bhp
4903TI002 KN
according to ISO (3.1 kW) at (3.3 kW) at
7293 9,500 rpm 9,500 rpm
Idling speed 2,800 rpm 2,800 rpm
The one-piece shroud is fastened with three screws.
This provides easy access to the air filter and High speed setting
cylinder. when performing
13,000 rpm 13,000 rpm
repairs (with guide
. Loosen screws (1) and remove shroud (2) bar and saw chain)
1.4 Anti-vibration system 2.2 Weight
dry, without bar and chain
MS 311: 14.10 lbs. (6.4 kg)
2 MS 391: 14.10 lbs. (6.4 kg)
3
2.3 Ignition system
Ignition module Electronically controlled,
with adjustment of the
4903TI003 KN
ignition timing
5 5 4 1 Spark plug
NGK BPMR 7 A
(interference
The new anti-vibration system consists of the Bosch WSR 6 F
suppressed)
springs (1) and (3), spring (2) with integral overload Electrode gap .020 in. (0.5 mm)
protection, the Cellasto AV element (4) and the two
stop buffers (5).
The combination of these elements reduces the
vibration level.
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2.4 Fuel system 2.6 Cutting attachment
Carburetor
All-position diaphragm carburetor 2.6.1 Guide bars STIHL ROLLOMATIC® E with
sprocket nose (with green label)
Standard setting with limiter cap Cutting lengths (3/8" pitch): 16, 18, 20 in.
(40, 45, 50 cm)
Low speed screw L: 1 turn open
Groove width: 0.050 in. (1.3 mm)
or 0.063 in.
High speed screw H: 3/4 turn open
(1.6 mm)
(max. to stop)
Sprocket nose: 10- or 11-tooth
Basic setting (with pre-installed limiter cap on 2.6.2 Oilomatic saw chains (with green label)
the high speed screw)
STIHL RAPID™ Micro™ Comfort 3 (33 RMC3)
Low speed screw L: 1 turn open STIHL RAPID™ Micro™ Comfort 3 (36 RMC3)
STIHL RAPID™ Super Comfort 3 (33 RSC3)
High speed screw H: 1 turn open
STIHL RAPID™ Super Comfort 3 (36 RSC3)
Pitch: 3/8" (9.32 mm)
Fuel mixture
Drive link gauge: 0.050 in. (1.3 mm) or
See Instruction Manual 0.063 in. (1.6 mm)
Fuel tank capacity: 20.3 oz (0.60 l)
2.6.3 Recommended bar and chain
combination
2.5 Chain lubrication
20 in. (50 cm) - 33 RMC3-72 saw chain and 3003
Oil pump: Speed-controlled oil 008 8921 guide bar.
pump – additional
manual oil flow control 2.6.4 Chain sprocket
Oil tank capacity: 11.8 oz (0.35 l)
7-tooth for 3/8" (rim sprocket)
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Technical Information 27.2009 Page 5
3. Special tool and service
accessories
3.1 Special tools
The following special tools must be procured.
4903TI004 KN
Item Designation Part number Use
1 Flange 1140 890 1200 Leakage test
3.2 Servicing accessories
Designation Part number Use
Set of carburetor parts 1140 007 1004 Carburetor repairs
Grease (225 g tube) 0781 120 1111 Oil seals, oil pump drive, sprocket bearings, chain tensioner
bearing and sliding surfaces for throttle trigger, brake lever
and trigger interlock
Standard commercially
available CFC and HFC-free
Cleaning crankshaft stub and cone on flywheel
solvent-based degreasing
agent
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3.3 Special accessories for the user
Designation Part number Use
Cover plate kit 1140 007 1003 Prevents powdered or drifting snow from entering the
machine under extreme winter conditions (temperatures
under 14°F (-10 °C), powdered or drifting snow)
4. Servicing Adjustment
The specific national safety regulations and the Adjust the specified engine speeds within a
safety instructions in the Instruction Manual must be tolerance range of +/- 200 rpm as follows
observed when starting and operating the chain 1. Set speed to 3,300 rpm with idle speed
saw. adjusting screw (LA)
Only use the chain saw with the shroud mounted – 2. Turn the low speed screw (L) clockwise or
otherwise there is a risk of engine damage due to counterclockwise to set the highest speed.
overheating. If this speed is greater than 3,700 rpm, stop and
start again with step 1.
4.1 Carburetor 3. Set the speed to 3,300 rpm again with idle
With this carburetor, the high speed screw H can speed screw (LA)
only be adjusted by the user within a range of an 4. Set the speed to 2,800 rpm with low speed
approx. 3/4 turn. screw (L)
5. Set high speed setting when performing
4.1.1 Basic setting (with limiter cap fitted on repairs (with guide bar and saw chain) of
the high speed screw) 13,000 rpm with the high speed screw (H)
. Perform the basic setting of the adjusting 6. Secure the limiter cap
screws.
Low speed screw L: 1 turn open
High speed screw H: 1 turn open
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Technical Information 27.2009 Page 7
4.2 Setting of throttle shutter / air flap 4.3 Fuel system – barbed connectors
No adjustments to the control system of the air flap To ensure no leaks of the fuel system:
are required. The correct position of the air flap can
. Install or remove the fuel hoses, by hand
be visually checked as follows:
whenever possible, in the direction of the
Throttle shutter connector in order to avoid damage to the
(throttle trigger barbed connector – sharp-edged pliers,
position) Air flap screwdrivers, etc., may not be used – also, do
Idle completely closed not cut open fuel hoses with a knife or similar
aids
Idle to full throttle closed to completely
open1) . Do not reuse fuel hoses after disassembly, but
Full throttle completely open1) instead always replace them with new hoses –
Cold start l completely closed fuel hoses can be overstretched when being
detached
Warm start n approx. 5° open
. Mount new fuel hoses dry or using press fluid
1) OH 723 – 0781 957 9000. Other press fluids are
The air flap must be moveable in both directions not permitted and may lead to fuel hose damage
(open and close) and always return to the starting
position . When using press fluid OH 723, apply press
fluid OH 723 to the ends of the hose and the
Before adjustment and maintenance work on the connectors and press the new hoses onto the
carburetor – check air flap barbed connectors
Notes regarding press fluid OH 723
Press fluid OH 723 produces a lubricant film that
simplifies assembly. The lubricant evaporates after
a short time – the hose is firmly seated.
1 Never use fuel, oil or grease as a lubricant. Fuel, oil
and grease do not evaporate – the hose may come
loose.
0001TI006 KN
. In idle position, the air flap (1) must make
contact with the housing all round and seal the
air duct.
. Clean dirty air flap with STIHL special-purpose
cleaner or a non-flammable cleaning liquid – do
not damage the air flap
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4.4 Tightening torques The repair times are specified in minutes.
The tightening torques for MS 311 and MS 391 are Type of repair MS 311
listed in the Service Manual for STIHL MS 311 and MS 391
MS 391.
1 Replace crankcase, crankcase 135
gasket or re-seal crankcase.
4.5 Service notes
Includes air leak test.
The Service Manual STIHL MS 311 and MS 391 is 2 Replace engine housing or cylinder 15
available for servicing and repair of the STIHL shroud.
MS 311 and MS 391. 3 Replace crankshaft main 120
bearing(s). Includes air leak test.
4.6 Serial number
4 Replace crankshaft seal(s). 60
Includes air leak test.
5 Perform engine air leak test. 30
6 Replace cylinder and/or piston. 60
Includes air leak test and repair of
components causing failure.
7 Replace ignition module or 30
flywheel. Includes stop circuit test.
8 Replace fuel tank line, tank vent, or 25
fuel pick-up body.
0001TI007 KN
9 Replace intake manifold or intake 30
flange, including leak test.
10 Repair or replace carburetor. 35
The serial number is on the side of the crankcase. Includes fuel system testing.
11 Replace fuel tank housing. 35
4.7 Repair times
12 Replace oil pick-up/delivery line. 30
The specified repair times apply for trained and Includes oil output test.
qualified personnel as well as for properly equipped 13 Replace oil pump and/or drive 30
repair shops. gear. Includes oil output test.
14 Replace rear handle frame or 20
handle housing.
15 Repair or replace rewind starter. 20
16 Repair or replace clutch, clutch 20
shoes or clutch springs.
17 Repair chain brake, including 35
check for proper function.
18 Replace muffler. 15
19 Replace air filter or filter housing. 15
22 Repair or replace stop switch. 20
Includes circuit testing.
25 Replace front handle 15
40 Miscellaneous repairs and other 15
repairs not listed.
45 Handling allowance only-no labor. 10
50 No labor. 0
© ANDREAS STIHL AG & Co. KG, 2009 Technical Documentation
D1/MTK-bl
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Extracted from the manufacturer's 2012 service catalogue. Most of these PDFs embed fonts with a shifted character map, so the text above was recovered rather than copied — read it as a faithful but imperfect transcription, and treat the page image above each block as the authority where the two disagree — the figures exist only there, because they are vector drawings that text extraction cannot keep.