Technical Information · issue 4 of 1995
New FR 108 Backpack Brushcutter
IssueTI 4/1995
Full text
Page 1 of 11
Technical Information
04.95
New STIHL FR 108 Backpack Brushcutter - Series 4135
1.====General description
The new FR 108 backpack brushcutter has Applications of the FR 108 range from cutting wild
been designed for professional applications. growth, weeds, scrub and shrubs, to cutting and
It helps save time and effort and offers profes- thinning young stands as well as limbing standing
sional-class handling characteristics. timber up to a height of 8 ft (2.4 m) and performing
grafting cuts in orchards.
360TII001
Ergonomic controls are designed to ensure The engine is pivot-mounted so that it can follow
extremely simple and reliable operation of the unit. the movements of the drive tube and thus reduce
The handle can be moved up or down the shaft to the mechanical loads on the flexible drive shaft.
the most comfortable operating position. Anti- The FR 108 uses the basic design concept of the
vibration elements are installed between the FR 106. The new engine has a power output of
engine and support frame and are designed to 1.1 kW (1.5 bhp), which is the same as the pre-
keep vibrations away from the operator. These vious unit , but now has more torque and is
features are designed to help the operator work service-friendlier. Weighing only 10.3 kg (22.7 lb),
more effectively and more safely with a minimum the FR 108 is about 0.5 kg (1.1 lb) lighter than the
of fatigue. FR 106.
)Technical Information 04.95 - Page 2
2.=======Cutting tools
1===================2
The following cutting tools are approved for use
681FK003
681FK001
with the backpack brushcutters:
3
1=pqfei=?pupercut 2-2" cutting head
4002 710 2142
681FK006
2=pqfei=?pupercut 20-2" cutting head 5
4
4002 710 2162
3=pqfei=?^utocut 25-2" cutting head
QMMO=TNM=ONMU==========================================================6
681FK007
4=pqfei=?^utocut 30-2" cutting head
4002 710 2107
5=pqfei=?molymatic 30-2" cutting head
7
QMMO=TNM=ONOM============================================================================================8
681FK012
6=pqfei=?molycut 40-3" cutting head
4111 710 2100
7=pqfei=?cixed Line Head"
681FK013
4001 713 2100
8=`utting blade OPMJQ==============================10
4001 713 3801
9=`utting blade 230-8
4001 713 3803
10=_rush knife 250-3
4112 713 4100
fo 11
11=`ircular saw blade 200 (scratcher toothF==============12
4112 713 4201
12=`ircular saw blade 200 (chisel tooth)
4112 713 4203
* Only approved for limbing standing timber up
to a height of 8 ft (2.4 m)
Important!
For safety reason this brushcutter must not be
used for felling operations.
3.=======Technical description
3RZHUKHDG
• Compact two-stroke engine.
• Smooth exterior surfaces help prevent dirt
accumulating and make cleaning much easier.
• Housing is designed to help prevent contact
with hot parts of the engine.
&UDQNFDVH
• Two-part aluminum die casting. Two oil seals
with dust lips.
&UDQNVKDIW
• Three-part assembly which is pressed together
prior to final machining.
)Technical Information 04.95 - Page 3
3LVWRQ
• Aluminum alloy piston with two compression
rings.
• Piston pin is supported in a needle cage and
located by hookless wire snap rings.
&\OLQGHU
• Special aluminum alloy.
• Bore electroplated with a extremely wear
resistant special alloy.
&DUEXUHWRU
• Diaphragm carburetor, secured to cylinder with
thermally insulated mounting.
Air filter
• Flat foam (1) and felt (2) elements.
• No tools are required to remove and refit the
filter cover (3).
Exhaust muffler
• Large volume with fire screen. fo 2
1
Ignition system===================================================P
357TI004
• Electronic system consisting of flywheel and
ignition module with integral trigger unit.
• Flywheel does not have to be removed for
access to ignition module.
Rewind starter
• Single pawl system.
STOP START
&RQWUROV
• As on STIHL FR 106
• Control handle with throttle trigger lock (4),
throttle trigger (5), slide control (6).
• Starting throttle, run and stop positions selected
with one hand.
5 4 360TI002
&OXWFK
• Clutch shoes with linings, pivot mounted on
flywheel.
AV system
• As STIHL FR 106. System isolates
vibration so that it is confined mainly to the
engine.
Drive shaft
• Rigid shaft supported in six bushings.
*HDUKHDG
• Same as models FS 66 through 108, FR 106.
)Technical Information 04.95 - Page 4
Cutting tool mounting =7
• As on models FS 74, 76, 86, 88, 106 and 108,
FR 106, with M10 x 1 left-hand thread.
7
357TI006
Deflector for cutting heads =8=, universal
deflector =9======================================================NN
• Screwed rigidly to gear head flange.
• Fixed position relative to cutting tool. 11 8
10
Skirt =10
• Extends universal deflector (9). Must always be
fitted before using cutting heads. fo
Line limiting blade =11
• Trims surplus nylon line to correct length. Must
9
357TI007
always be fitted before using cutting heads with
nylon line.
Limit stop =12= for circular saw blades
• Screwed rigidly to gear head flange. 12
• Fixed position relative to cutting tool for good
protection.
• 0XVW always be fitted before using circular saw
blades.
357TI010
4.=======Specifications
4.1======Powerhead
4.1.1=Engine
Displacement: 34.4 cm3 (2.1 cu.in)
Bore: 37 mm (1.46 in)
Stroke: 32 mm (1.26 in)
Engine power to ISO 8893: 1.1 kW (1.5 bhp)
)Technical Information 04.95 - Page 5
Full-load engine speed
without cutting tool: 12,000 rpm
Max. speed of output shaft
(tool mounting): 9,000 rpm
Clutch engages at: 3,500 rpm
Idling speed: 2,800 rpm
Rewind starter: Single pawl system
Rewind spring
- Tension: 7 turns of rope rotor
- Spare travel: min. 1/2 turn of rope rotor
Starter rope
- Diameter: 3.5 mm (0.14 in)
- Length: 800 mm (31.5 in)
4.1.2=Fuel system
Air filter: Foam and felt elements
Fuel capacity: 0.69 l (1.45 US pt)
4.1.3=Ignition system
Air gap:
Ignition timing:
0.1 - 0.5 mm (0.004 - 0.020 in)
1.45 ... 2.05 mm (0.06 - 0.08 in) B.T.D.C. at 8,000 rpm
Length of ignition lead: 220 mm (8 3/4 in)
Spark plug (suppressed): Bosch WSR 6 F or
NGK BPMR 7 A;
Heat range 200;
Electrode gap 0.5 mm (0.020 in);
Spark plug thread M 14 x 1.25;
Thread length 9.5 mm (0.37 in)
4.2===Gear head
Type: Helical bevel gear drive
Gear ratio: 1.33
Lubrication: STIHL gear lubricant 0781 120 1117
4.3===Weight
without cutting tool and deflector: 10.3 kg (22.7 lb)
4.4===Cutting tools
For approved cutting tools see chapter 2.
)Technical Information 04.95 - Page 6
4.4.1=Nylon line for cutting heads
Line diameter/ Length Part No. Application
color
0.095 in / 50 ft 0000 930 2587 Supercut 2-2, Supercut 20-2,
orange 1/2 lb. 0000 930 2582 Autocut 25-2, Autocut 30-2,
1 lb. 0000 930 2579 Polymatic 30-2, Fixed Line Head
3 lb. 0000 930 2246 Polycut 40-3
5 lb. 0000 930 2247
0.105 in / red 35 ft 0000 930 2586 Fixed Line Head, Polycut 40-3
1 lb. 0000 930 2578
4.4.2=Thermoplastic blades for Polycut 40-3
Set of 12 blades 4111 007 1001
4.4.3=Sharpening aids for metal cutting tools
Part Name Part No. Application
File holder; 5605 750 4343 Circular saw blade 200 (chisel tooth)
including:
Round file (Ø 5.5 mm) 0811 411 8108
Sharpening template 0457 342 2629 Brush knife 250
STIHL balancer 5910 850 2600 universal
4.5===Special accessories
4.5.1=For user
Part Name Part No. Application, Remarks
Universal deflector kit 4119 007 1013 Kit includes: Deflector, skirt, line limiting blade
and mounting hardware
Universal deflector 4119 713 4500 Deflector only
Deflector kit for cutting heads 4133 007 1002 Kit includes: Deflector, line limiting blade and
mounting hardware
Deflector for cutting heads 4133 710 8101 Deflector only
Limit stop for circular saw blades 4117 710 8200 Limit stop with mounting hardware
)Technical Information 04.95 - Page 7
4.5.1=For user =cont¶d
Part Name Part No. Application, Remarks
Transport guard for
metal cutting tools 4119 790 3906 Cutting blade 230-4, 230-8,
Brush knife 250-3
4119 790 3901 Circular saw blade 200 (scratcher / chisel tooth)
STIHL multipurpose grease Rigid drive shaft in tube
- Tube 80 g (3 oz) 0781 120 1109
STIHL gear lubricant Gear head
- Tube 80 g (3 oz) 0781 120 1117
4.5.2=For service shop
Carburetor parts kit4132 007 1061
Dirko sealant 0783 830 2120
Sealing crankcase
5.====Testing and setting data
5.1===Carburetor adjustment
High speed adjusting screw H: back off 1 full turn
Low speed adjusting screw L: back off 1 full turn
(basic setting, screws initially
hard against their seats)
Full-load engine speed
without cutting tool: 12,000 rpm
Idling speed: 2,800 rpm
Carburetor leakage test:
- carb closing pressure: 0.8 bar (11.6 psi)
5.2===Engine
Crankcase leakage test;
- at gauge pressure: 0.5 bar (7.25 psi)
- under vacuum: 0.5 bar (7.25 psi)
)Technical Information 04.95 - Page 8
5.3 Tightening torques
Fastener Thread For component Torque down to
size Nm lbf.ft
Spline screw IS-M 5x30 Crankcase 10.5 7.7
Spline screw IS-M 5x16 Cylinder to crankcase 10.0 7.4
Hex. head screw M 8x20 Clutch shoes 17.0 12.5
Spline screw IS-M 5x16 Muffler to cylinder 10.5 7.7
Spline screw IS-M 5x12 Muffler to crankcase 10.5 7.7
Spline screw IS-M 4x12 Cover plate to muffler 3.5 2.6
Spline screw IS-M 5x16 Clutch housing 9.5 7.0
Spline screw IS-M 5x16 Support to clutch housing 7.5 5.5
Flange screw IS-M 5x14 Fuel tank 5.5 4.0
Hexagon nut M8 Flywheel 17.0 12.5
Hexagon nut M8 Carrier 17.0 12.5
Spline screw IS-M 5x16 Starter cover (top) 5.5 4.0
Spline screw IS-M 5x16 Support/starter cover (bottom) 7.5 5.5
Special spline screw IS-P 5.5x12 Rope rotor 2.5 1.8
Spline screw IS-M 5x20 Ignition module 7.5 5.5
Spark plug M 14x1.25 19.0 14.0
Spline screw
Spline screw
IS-M 5x22
IS-M 5x25
Carburetor fo
Spacer flange to cylinder
5.5
5.5
4.0
4.0
Spline screw IS-M 4x25 Adjusting screw in tensioner -
Spline screw IS-M 5x16 Tensioner to spacer flange -
Spline screw IS-M 5x12 Shroud 5.5 4.0
Spline screw IS-P 4x19 Two halves of control handle 2.0 1.5
Spline screw IS-P 4x35 Guard to handle molding 2.0 1.5
Spline screw IS-M 5x16 Clamp on control handle 3.5 2.6
Spline screw IS-M 6x25 Clamp screw in
sleeve (drive tube) 7.0 5.2
Spline screw IS-M 5x10 Setscrew in
sleeve (drive tube) 3.5 2.6
Spline screw IS-M 5x20 Clamp screws in gearhead 8.0
Spline screw IS-M 5x10 Bracket to support frame 3.5 2.6
Spline screw IS-M 5x10 Clamp to support frame 3.5 2.6
Spline screw IS-M 6x12 Bearing housing to support frame 10.0 7.4
Spline screw IS-M 6x12 Shackle to support frame 7.0 5.2
Hexagon nut M6 Rubber buffer 5.0 3.7
Hex. head screw M 10x20 Engine mounting 30.0 22.0
Spline screw IS-M 6x12 Clamp for loop handle
and strain relief cord 6.0 4.4
Screw plug IS-M 11x10 Filler opening for grease (gearhead) 10.0 7.4
Screws, nuts M4 all others 2.5 1.8
Screws, nuts M5 all others 4.5 3.3
)Technical Information 04.95 - Page
6.====Testing and servicing tools
6.1===New special tools
22,5
26
357TI008
Part Name Part No. Key fo Application Rem.
Installing tool
for AV rubber element
Ø 22.5 mm (0.88 in),
Ø 26 mm (1.02 in) 4135 893 4900 1 FR 108, FS 108 1)
5HPDUNV
1) See FS 88, 108 and FR 108 shop manual for use instructions
6.2===Existing special tools
Part Name Part No. Application Rem.
Locking screw for 4112 893 1200 Blocking the crankshaft
piston
Press sleeve 1129 893 2400 Installing oil seal at clutch side
Press sleeve 4112 893 2400 Protecting oil seal at starter side
Press sleeve 1115 893 4600 Installing oil seal at starter side
Press arbor 4117 893 4700 Installing piston pin
Clamping strap 0000 893 2600 Compressing piston rings
Wooden assembly block 1108 893 4800 Fitting piston
Crankcase and 1106 850 2905 Testing crankcase and
carburetor tester carburetor for leaks
- Nipple 0000 855 9200 Carburetor leakage test
- Fuel line 1110 141 8600 Carburetor leakage test
Vacuum pump 0000 850 3501 Crankcase leakage test
Sealing plate 0000 855 8106 Sealing exhaust port for
leakage test
)Technical Information 04.95 - Page 10
6.2====Existing special tools =cont¶G
Part Name Part No. Application R
Test flange 1113 850 4200 Leakage test 1)
Setting gauge 1111 890 6400 Setting air gap between ignition module
and flywheel 2
Puller 0000 890 4400 Removing oil seals
- Jaws (profile 3.1) 0000 893 3706
Installing tool 10 5910 890 2210 Fitting hookless snap rings in piston
Removing tool 4119 890 4600 Removing crankshaft (starter side) 3)
Socket, 13 mm 5910 893 5608 Crankshaft nut (carrier, flywheel)
Torque wrench 5910 890 0301 Screwed assemblies (0.5 to 18 Nm)
5910 890 0302 4)
Torque wrench 5910 890 0311 Screwed assemblies (6 to 80 Nm)
5910 890 0312 4)
Assembly hook 5910 893 8800 Removing pickup body
T-handle screwdriver 5910 890 2400 IS spline screws
QI-T27x150
Crimping tool 5910 890 8210 Wire connectors, lugs, etc.
Assembly stand 5910 850 3100 Holds powerhead in position for repairs
- Flange
- Clamping plate
5910 893 2500
5910 890 2100
Settings as for FS 106 or FS 108
Socket 0812 542 2104 Cylinder base screws
Press arbor 4119 893 7200 Removing and installing main bearings
Pliers C19 0811 641 8380 Internal circlips (gearhead) 5)
Pliers A10 0811 611 8200 External circlips (clutch drum,
gearhead, drive pinion)
Circlip pliers 0816 610 1495 External circlips (clutch drum)
Press arbor 1108 893 4700 Removing clutch drum
Press arbor 1118 893 7200 Removing and installing ball bearing in
clutch housing
5HPDUNV
1) Flange 1128 850 4200 may be used as an alternative.
2) Setting gauge 4118 890 6401 may be used as an alternative.
3) Existing tools must be modified as shown in the illustration. This modification does not affect or
restrict the tool’s other applications.
4) With optical/acoustical signal.
5) C8 Pliers 0816 630 1452 may be used as an alternative.
357TI009
)Technical Information 04.95 - Page 11
7.====Important=======================================`ode Repair procedure FS 88
FS 108
If the unit is started up in the course of repairs ===============================================co=NMU
or maintenance work, it is essential to strictly
observe all local and national safety regulations=====N====`r~nkc~seI=phort=_lock===================OKN
as well as the safety precautions outlined in
the owner¶s manual.===================================O====`rankshaft and/or Bearings 2.2
3 Crankcase Gasket, Sealing 2.0
8.====Service note
4 Crankshaft seals 0.7
Refer to the service manual for servicing and 5 Cylinder and/or Piston 0.8
repair procedures on the FR 108.
For the first time ever the new service manual for 6 Ignition 0.5
this brushcutter does not include the chapters
"Servicing the Carburetor", "Troubleshooting" or 7 Fuel Hose, Fuel Supply 0.5
other standard repair jobs. These servicing and
8 Gear Box, Arbor Assy 0.6
repair procedures are described in a separate
handbook which will be available in the foreseeable 9 Carburetor 0.7
future. The appropriate chapters in the service
manual for models FR and FS 106 can be used as 10 Fan Housing, Clutch Housing 0.8
a reference until the new handbook is published.
11 Front Handle, Throttle 0.6
8.1===Repair times
12
Recoil Starter 0.5
13 Clutch 0.5
The specified repair times assume that the work is
performed by trained personnel in a properly 14 Drive Tube, Drive Shaft 0.5
equipped service workshop.
15 Muffler 0.4
The repair times are in tenths of an hour
16 Air Filter, Filter Cover 0.3
(0.1 = 6 minutes).
17 Stop Switch 0.4
Note:=qhis table for the new brushcutters 18 Fuel Tank 0.4
can be added to the STIHL repair times table.
19 Replace Arbor Gears 0.8
20 Misc. Repairs 0.5
✂
Waiblingen, 22.02.1995 Andreas Stihl - D1/MTK-na
1995 Andreas Stihl Technical Documentation Page 2 of 11
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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.