Stihl BT 45 Manuel utilisateur
STIH)
STIHL Components 4140
BT 45 2009-07
1BT 45
q
© ANDREAS STIHL AG & Co. KG, 2009
Contents
1. Introduction 2
2. Safety Precautions 3
3. Specifications 4
3.1 Fuel System 4
3.2 Gearbox 4
3.3 Tightening Torques 5
4. Troubleshooting 7
4.1 Clutch 7
4.2 Rewind Starter 8
4.3 Fuel System 9
4.4 Engine 11
5. Shroud/Housing
Parts 12
5.1 Handle Housing 12
5.2 Clutch 13
5.2.1 Engine 14
5.3 Muffler/Spark
Arresting Screen 14
6. Rewind Starter 15
6.1 General 15
6.2 Removing and
Installing 15
6.3 Starter Cup 16
6.3.1 Rope Rotor 16
6.4 Replacing the
Rewind Spring 17
6.4.1 Tensioning the Rewind
Spring 18
6.5 Starter Rope 18
6.6 Starter Rope
Guide Bush 19
6.7 Pawl 20
7. Throttle Control 20
7.1 Throttle Trigger 20
7.2 Replacing the Throttle
Cable 21
7.3 Stop Switch 21
8. Fuel System 22
8.1 Air Filter 22
8.1.1 Removing and
Installing 22
8.1.2 Choke Shutter 22
8.2 Carburetor 23
8.2.1 Leakage Test 23
8.2.2 Removing and
Installing the
Carburetor 24
8.3 Spacer Flange 25
8.4 Servicing 25
8.4.1 Manual Fuel Pump 25
8.4.2 Metering Diaphragm 26
8.4.3 Inlet Needle 27
8.4.4 Fixed Jet 27
8.4.5 Pump Diaphragm
and Fuel Strainer 28
8.4.6 Adjusting 28
8.4.7 Basic Setting 30
8.5 Tank Vent 30
8.5.1 General 30
8.5.2 Replacing 31
8.6 Fuel Tank 31
8.6.1 Pickup Body 31
8.6.2 Hoses 32
9. Gearbox 32
9.1 Removing and
Installing 32
9.2 Diassembling and
Assembling 33
10. Special Servicing
Tools 40
11. Service Accessories 41
2BT 45
This service manual contains
detailed descriptions of all the
typical repair and servicing
procedures for the BT 45 which is
based on the series 4140
powerhead.
You will find detailed descriptions of
procedures for servicing and
repairing engine components in the
service manual for the “Series 4140
Powerhead“.
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" in this manual
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 chapter
"Special Servicing Tools" of 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.
Symbolsareincludedinthetextand
pictures for greater clarity.
The meanings are as follows:
In the descriptions:
:= 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)
b4.2
Reference to another chapter, i.e.
chapter 4.2 in this example.
In the illustrations:
Pointer
Direction of movement
Service manuals and technical
information bulletins are intended
exclusively for the use of properly
equipped repair shops. They must
not be passed to third parties.
Always use original STIHL
replacement parts.
They can be identified by the
STIHL part number,
the STIH) logo
and the
STIHL parts symbol (
This symbol may appear alone on
small parts.
1. Introduction
3BT 45
If the engine 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.
Gasolineisanextremelyflammable
fuel and can be explosive in certain
conditions.
Improper handling may result in
burns or other serious injuries.
Warning!
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.
2. Safety Precautions
4BT 45
3. Specifications
3.1 Fuel System Carburetor: Diaphragm carburetor
Carburetor leakage test
at gauge pressure: 0.8 bar (11.6 psi)
Checking operation of tank vent
at gauge pressure: 0.3 bar (4.4 psi)
under vacuum: 0.05 bar (0.725 psi)
Fuel: see instruction manual
Octane rating: min. 90 RON
Fuel mixture: Regular brand-name gasoline and
STIHL 50:1 two-stroke engine oil or
brand-name two-stroke engine oil
Mix ratio: 50:1 with STIHL two-stroke engine oil
Fuel mix for units with catalytic
converter: Use only STIHL 50:1 two-
stroke engine oil with lead-free
gasoline!
3.2 Gearbox Type: Multi-stage spur gear drive with
straight teeth
Gear ratios: 1 = 11.3:1
2 = 3.8:1
R = 12.7:1
Bearings: Deep-groove ball bearings
Lubrication: STIHL gear lubricant for brushcutters
(total capacity 20 g)
5BT 45
3.3 Tightening Torques
DG and P (Plastoform) screws are used in polymer and lightmetal 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
lbf.ft Nm
M14x7 Stub/muffler 7.5 10.0
Screw IS-DG5x24 Spacer flange/cylinder 4.4 6.0
Screw IS-DG5x20Z Fan housing/spiral housing 4.4 6.0
Screw IS-DG5x24 Spiral housing/crankcase 4.4 6.0
Screw IS-DG5x24 Spiral housing/engine pan 4.4 6.0
Screw IS-DG5x20Z Fan housing/spiral housing 4.4 6.0
Screw M4x8 Guide plate/gear housing 3.0 4.0
Screw IS-DG5x60 Muffler/cylinder 6.6 9.0
Screw M6x25LH Lock screw, chuck/output shaft 7.5 10.0
1/2“-20 Chuck/output shaft 26 35.0 1)
Screw IS-P4x14 Rotary knob/driver, gearbox 0.75 1.0
Fastening nut M5 Filter cover/handle housing/screw 1.5 2.0
Screw IS-DG5x20 Gear housing, right/left 5.9 8.0
Screw IS-DG5x24 Gear housing/crankcase 5.9 8.0
Screw IS-DG5x24 Gear housing/engine pan 5.9 8.0
Screw IS-DG5x24 Handle housing, left/right 2.6 3.5
Screw IS-DG5x16 Shroud/gearbox 2.6 3.5
Nut M5 Manifold/carburetor/flange/screw 2.6 3.5
M8x1.25L Carrier/crankshaft 12.5 17.0
Nut M12x1.25 Friction clutch 10.5 14.0
M14x1.25 Spark plug 15 20.0
Remarks:
1) Install screw with medium-strength Loctite 243
6BT 45
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.
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 settings for polymer: Plastoform screws max. 600 rpm
DG screws max. 500 rpm
Important:
Do not mix up screws with and without binding head
7BT 45
4. Troubleshooting
4.1 Clutch
Condition Cause Remedy
Tool stops at full throttle
under load Clutch shoes badly worn Install new clutch shoes or a new
clutch
Tool runs at idle speed Idle speed too high Readjust idle speed screw
(counterclockwise)
Clutch springs stretched or
fatigued Fit new clutch springs
Spring hooks broken Fit new clutch springs
Loud noises Clutch springs stretched or fatigued Replace all clutch springs
Clutch shoe retainer (carrier)
broken Fit new retainer (carrier) or clutch
Clutch shoes and carrier worn Install a new clutch
8BT 45
4.2 Rewind Starter
Condition Cause Remedy
Starter rope broken Rope pulled out too vigorously as
far as stop or over edge, i.e. not
vertically
Fit new starter rope
Normal wear Fit new starter rope
Rewind spring broken Spring overtensioned – no reserve
when rope is fully extended Fit new rewind spring
Very dirty or corroded Fit new rewind spring
Starter rope can be pulled out
almost without resistance
(crankshaft does not turn)
Guide peg on pawl or pawl itself
is worn Fit new pawl
Spring clip fatigued Fit new spring clip
Starter rope is difficult to pull and
rewinds very slowly Starter mechanism very dirty
(dusty conditions) Thoroughly clean complete starter
mechanism
Lubricating oil on rewind spring
becomes viscous at very low
outside temperatures (spring
windings stick together)
Coat rewind spring with a standard
solvent-based degreasant
(containing no chlorinated or
halogenated hydrocarbons). Then
pull rope carefully several times
until normal action is restored
9BT 45
4.3 Fuel System
Condition Cause Remedy
Engine stalls at idle speed Idle jet bores or ports blocked Clean jet bores and ports and blow
clear with compressed air
Idle jet too rich Screw down low speed screw
slightly (see Adjusting the
Carburetor)
Setting of idle speed screw
incorrect – throttle shutter
completely closed
Reset idle speed screw correctly
Engine speed drops quickly under
load – low power Air filter plugged Clean the air filter or replace if
necessary
Tank vent faulty Clean the tank vent or replace if
necessary
Leak in fuel line between tank and
fuel pump Seal or renew connections and fuel
line
Pump diaphragm damaged or
fatigued Fit new pump diaphragm
Main jet bores or ports blocked Clean the bores and ports
Fuel pickup body dirty Install new pickup body
Engine will not idle,
idle speed too high Throttle shutter opened too wide by
idle speed screw Reset idle speed screw correctly
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6
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