Technical Information · issue 37 of 1994
New brushcutters
Model: FS 88 FS 108
IssueTI 37/1994
Full text
Page 1 of 12
Technical Information
37.94
New brushcutters STIHL FS 88 - Series 4126
STIHL FS 108 - Series 4135
1. General description
The new STIHL FS 88 and 108 brushcutters are
handy, lightweight units designed for more deman-
ding occasional users, landscape gardeners, appli-
cations in municipalities as well as agriculture and
forestry. They help save time and effort and offer
professional-class handling characteristics.
Engine power and displacement
- STIHL FS 88: 0.9 kW (1.2 bhp)
25.4 cm3 (1.55 cu.in)
- STIHL FS108: 1.1 kW (1.5 bhp)
34.4 cm3 (2.1 cu.in)
The following versions are available:
- STIHL FS 88 (version with bike handle)
357TI001
- STIHL FS 88 R (version with loop handle)
- STIHL FS 108 (version with bike handle)
- STIHL FS 108 R (version with loop handle)
FS 88 FS 88 R
The STIHL FS 88 and 108 are suitable for general
cutting work on large areas, including weeds, reed,
brush, wild growth, scrub, shrubs and bushes as
well as sawing small-sized wood.
The ergonomically designed controls permit
extremely simple and reliable operation of the
units. The loop or bike handle can be moved up or
down the shaft to the most comfortable operating
position. An efficient antivibration element is
installed between the shaft and engine to keep
vibrations away from operator. All these features
help the user to work more safety with a minimum
of fatigue.
The design concept of the FS 88 and 108 is
based models FS 86 and 106, but the new
engines provide higher torques and are service-
357TI002
friendlier. These new brushcutters round off the
upper end of STIHL’s semi-professional line.
FS 108 FS 108 R Page 2 of 12
Technical Information 37.94 - Page 2
2. Cutting tools and attachments
1 2
The following cutting tools are approved for use
681FK003
681FK001
with these brushcutters:
3
1 STIHL "Supercut 2-2" cutting head
4002 710 2140
681FK006
2 STIHL "Supercut 20-2" cutting head 5
4002 710 2162 4
3 STIHL "Autocut 25-2" cutting head
4002 710 2108
681FK007
4 STIHL "Autocut 30-2" cutting head 6
4002 710 2107
5 STIHL "Polymatic 30-2" cutting head
4002 710 2120 7
8
6 STIHL "Polycut 40-3" cutting head
4111 710 2100
681FK013
7 STIHL "Fixed Line Head" 9
4001 713 2100
8 Cutting blade 230-4
4001 713 3801 10
9 Cutting blade 230-8
4001 713 3803
10 Brush knife 250-3
4112 713 4100 11
11 Circular saw blade 200 (scratcher tooth)
4112 713 4201 13
12 Circular saw blade 200 (chisel tooth)
4112 713 4203
13 Cultivator attachment BC 30
4600 710 1500 12
Important!
For safety reasons metal cutting tools must not
be fitted or used on brushcutters with a loop
handle.
3. Technical description
Powerhead
• 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.
• Exhaust gases and heated cooling air are
diverted away from the operator.
Crankcase
• Two-part aluminium die casting. Two oil seals
with dust lips.
Crankshaft
• Three-part assembly which is pressed together
prior to final machining.
• Connecting rod and big end bearing are not
replaceable. Page 3 of 12
Technical Information 37.94 - Page 3
Piston
• Aluminium alloy piston with two compression
rings.
• Piston pin is supported in a needle cage and
secured by two hookless wire snap rings.
Cylinder
• Special aluminium alloy.
• Bore electroplated with an extremely wear
resistant special alloy.
Carburetor
• Diaphragm carburetor, secured to cylinder with
thermally insulated mounting.
Air filter
• Foam (1) and felt (2) elements.
• No tools are required to remove and refit the
filter cover (3).
Exhaust muffler
• Large volume for good silencing. fo
Ignition system
• Electronic system consisting of flywheel and
ignition module with integral trigger unit.
• Flywheel does not have to be removed for
access to ignition module. 2
1
Rewind starter 3
357TI004
• Single pawl system.
Controls
• As FS 72, 74, 76, 86 and 106
• Control handle with throttle trigger lock (4),
throttle trigger (5), slide control (6).
• Starting throttle, run and stop positions selected 6
with one hand.
Clutch 5
• Clutch shoes with linings, pivot mounted on
flywheel.
4
357TI005
AV system
• Layout as FS 74 and 76. System isolates
vibration so that it is confined mainly to the
engine. Page 4 of 12
Technical Information 37.94 - Page 4
Drive shaft
• Rigid shaft supported in six bushes.
Gearhead 7
• Same as models FS 66 through 106.
Cutting tool mounting (7)
• As on models FS 74, 76, 86 and 106,
with M10 x 1 left-hand thread.
357TI006
Deflector for cutting heads (8), universal
11
deflector (9)
• Screwed rigidly to gear head flange.
• Fixed position relative to cutting tool for good 11 8
protection. 10
Skirt (10)
• Extends universal deflector (9). Must always be
fitted before using cutting heads.
Line limiting blade (11) 9
357TI007
• Trims surplus nylon line to correct length. Must
always be fitted before using cutting heads with
nylon line.
4. Specifications
4.1 Powerhead
4.1.1 Engine
Model: FS 88 FS 108
Displacement: 25.4 cm3 (1.55 cu.in) 34.4 cm3 (2.1 cu.in)
Bore: 34 mm (1.34 in) 37 mm (1.46 in)
Stroke: 28 mm (1.10 in) 32 mm (1.26 in)
Engine power to ISO 8893: 0.9 kW (1.2 bhp) 1.1 kW (1.5 bhp)
Full-load engine speed
without cutting tool: 12000 rpm 12000 rpm
Max. speed of output shaft
(tool mounting): 8800 rpm 9000 rpm
Clutch engages at: 3700 rpm 3500 rpm
Idling speed: 2800 rpm 2800 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) Page 5 of 12
Technical Information 37.94 - Page 5
Model Cutting tool Sound pressure Sound power Vibration Vibration
level Lpeq level Lweq measurement measurement
to to
to to ISO 7916 ISO 7916
ISO 7917 1) ISO 10884 1) Idling speed Maximum RPM
(m/s2) (m/s2)
Handle Handle
dB (A) dB (A) right left right left
2)
FS 88 Cutting head 98 109 2.7 2.4 4.1 5.7
FS 88 2) Metal cutting tool 95 103 2.7 2.4 5.0 6.3
FS 88 R 3) Cutting head 98 109 2.5 2.0 6.3 6.3
FS 108 2) Cutting head 99 111 2.4 3.7 2.4 2.8
FS 108 2) Metal cutting tool 96 105 2.4 3.7 2.1 2.5
FS 108 R 3) Cutting head 99 111 2.2 2.5 8.5 7.4
1)
Data refers to averages obtained running at idling speed and maximum RPM in equal proportions
2)
Version with bike handle
3)
Version with loop handle
4.1.2 Fuel system fo
Air filter: Foam and felt elements
Fuel capacity: 0.69 l (1.45 US pt)
4.1.3 Ignition system
Air gap: 0.1 - 0.5 mm (0.004 - 0.020 in)
Ignition timing FS 88: 1.25 - 1.75 mm (0.05 - 0.07 in) B.T.D.C. at 8000 rpm
FS 108: 1.45 - 2.05 mm (0.06 - 0.08 in) B.T.D.C. at 8000 rpm
Length of ignition lead: 200 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 FS 88: 1.36
FS 108: 1.33
Lubrication: STIHL multipurpose grease 0781 120 1109
4.3 Weight
FS 88 FS 88 R FS 108
without cutting tool and deflector 6.5 kg 5.9 kg 7.1 kg
(14.3 lb) (13.0 lb) (15.6 lb)
4.4 Cutting tools and attachments
For approved cutting tools and attachments see 2. Page 6 of 12
Technical Information 37.94 - Page 6
4.4.1 Nylon line for cutting heads
Line diameter/ Length Part No. Application
color
2.4 mm 15 m (50 ft) 0000 930 2243 Supercut 2-2, Supercut 20-2,
(0.095 in) / 44 m (143 ft) 0000 930 2244 Autocut 25-2, Autocut 30-2,
orange 87 m (285 ft) 0000 930 2245 Polymatic 30-2, Fixed Line Head
261 m (855 ft) 0000 930 2246 Polycut 40-3
434 m (1425 ft) 0000 930 2247
2.7 mm 10.7 m (35 ft) 0000 930 2218 Fixed Line Head, Polycut 40-3
(0.105 in) / red 72.0 m (235 ft) 0000 930 2224
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
Flat sharpening file 0814 212 3310 Cutting blade 230-4, 230-8,
Brush knife 250,
Circular saw blade 200 (scratcher tooth)
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
Safety goggles depends on market
Shoulder strap 4119 710 9010
Full harness 4119 710 9001
Full harness L 4108 710 9001
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 Page 7 of 12
Technical Information 37.94 - 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 tooth/chisel tooth)
STIHL multipurpose grease Drive shaft
- Tube 80 g (3 oz) 0781 120 1109
- Tube 225 g (8 oz) 0781 120 1110
STIHL gear lubricant Gear head
- Tube 80 g (3 oz) 0781 120 1117
- Tube 225 g (8 oz) 0781 120 1118
STIHL low temperature lubricant Rewind spring in starter
- Bottle 100 ml (0.21 US pt) 0781 417 1315
4.5.2 For service shop
Carburetor
parts kit FS 86, 88 4117 007 1061
FS 106, 108 4132 007 1061
Gasket set FS 88 4126 007 1051
FS 108 4135 007 1050
Gasket panel (DIN A 3) 0457 281 2104
Dirko sealant 0783 830 2120 Sealing crankcase
Lube grease (370 g/13 oz tube) 0781 120 1111 Oil seals
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: 12000 rpm
Idling speed: 2800 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) Page 8 of 12
Technical Information 37.94 - Page 8
5.3 Tightening torques
Fastener Thread Torque down to
size For component Nm lbf.ft Rem.
Spline screw IS-M 5x25 Crankcase 10.5 7.7 FS 88
Spline screw IS-M 5x30 Crankcase 10.5 7.7 FS 108
Spline screw IS-M 5x16 Cylinder to crankcase 10.0 7.4
Flange screw M6 Clutch shoes 8.0 5.9 FS 88
Hex. head screw M 8x20 Clutch shoes 17.0 12.5 FS 108
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
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),
Support to clutch housing 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
Spline screw
M 14x1.25
IS-M 5x22 Carburetor
fo 19.0
5.5
14.0
4.0
Spline screw IS-M 5x25 Spacer flange to cylinder 5.5 4.0
Spline screw IS-M 4x25 Adjusting screw in clamp -
Spline screw IS-M 5x16 Clamp to spacer flange -
Spline screw IS-M 5x12 Shroud 5.5 4.0
Self-tapping screw B 2.9x25 Two halves of control handle
and left handle 2.0 1.5
Spline screw IS-M 5x30 Control handle and
left handle to bike handle 3.5 2.6
Spline screw IS-P 4x19 Two halves of loop handle 2.0 1.5
Spline screw IS-M 5x16 Clamp on control handle
(loop handle version) 3.5 2.6
Spline screw IS-M 6x20 Clamp screw in sleeve (AV) 7.0 5.2
Spline screw IS-M 5x20 Clamp screws in gearhead 8.0 5.9
Spline screw IS-M 6x25 Lower clamp to handle support 6.0 4.4
Spline screw IS-M 6x25 Upper clamp to handle support 6.0 4.4
Screw plug IS-M 11x10 Filler opening for grease (gearhead) 10.0 7.4
Spline screw IS-M 6x14 Clamp for harness 4.5 3.3
Spline screw IS-M 6x12 Clamp on loop handle 3.5 2.6
Spline screw IS-M 4x12 Setscrew in sleeve for
drive tube 3.0 2.2
Screws, nuts M4 all others 2.5 1.8
Screws, nuts M5 all others 4.5 3.3 Page 9 of 12
Technical Information 37.94 - Page 9
6. Testing and servicing tools
6.1 New special tools
22,5
26
25,4
24
(1")
357TI008
Part Name Part No. Key Application Rem.
Installing tool
for AV rubber element
Ø 22.5mm, 26mm
(0.88",1.02") 4135 893 4900 1 FS 108 1)3)
Ø 24mm, 25.4mm
(0.94",1") 4126 893 4900 2 FS 88 2)3)
Remarks
1) 22.5 mm (0.88") rubber element is for new brushcutters to be announced in the near future
2) Can be used for models FS 66, 72, 74, 76 and FC 72
3) See FS 88, 108 shop manual for use instructions Page 10 of 12
Technical Information 37.94 - Page 10
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 1)
Press arbor 1114 893 4700 Installing piston pin 2)
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
Test flange 1113 850 4200 Leakage test 3)
Setting gauge 1111 890 6400 Setting air gap between ignition module
Puller 0000 890 4400
and flywheel fo
Removing oil seals
4)
- Jaws (profile 3.1) 0000 893 3706
Installing tool 8 5910 890 2208 Fitting hookless snap rings in piston 2)
Installing tool 10 5910 890 2210 Fitting hookless snap rings in piston 1)
Removing tool 4119 890 4600 Removing crankshaft (starter side) 5)
Socket, 13 mm 5910 893 5608 Crankshaft nut (carrier, flywheel)
Remarks
1) FS 108
2) FS 88
3) Flange 1128 850 4200 may be used as an alternative.
4) Setting gauge 4118 890 6401 may be used as an alternative.
5) Existing tools must be modified as shown below. This modification does not affect or restrict
the tool’s other applications.
357TI009 Page 11 of 12
Technical Information 37.94 - Page 11
6.2 Existing special tools (cont’d)
Part Name Part No. Application Rem.
Torque wrench 5910 890 0301 Screwed assemblies (0.5 to 18 Nm)
5910 890 0302 6)
Torque wrench 5910 890 0311 Screwed assemblies (6 to 80 Nm)
5910 890 0312 6)
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 5910 893 2500
- Clamping plate 5910 890 2100 Settings as for FS 86 and FS 106
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) 7
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 1)
Press arbor
Press arbor
1111 893 4700
1118 893 7200
Removing clutch drum
Removing and installing ball bearing in
2)
clutch housing
Remarks
1) FS 108
2) FS 88
6) With optical/acoustical signal
7) C8 Pliers 0816 630 1452 may be used as an alternative.
7. Important
If the unit is started up in the course of repairs
or maintenance work, it is essential to strictly
observe all local and national safety regulations
and the safety precautions outlined in the
owner’s manual. Page 12 of 12
Technical Information 37.94 - Page 12
8. Service note
No. Repair procedure
Refer to STIHL FS 88 and 108 service manual for FS 88
descriptions of all repair procedures. FS 108
For the first time ever the new service manual for 1 Remove and refit engine 10
these brushcutters does not include the chapter
"Servicing the Carburetor". Servicing and repair 2 Crankcase, pressure test* 100
procedures for carburetors will be described in a
separate handbook which will be available in the 3 Crankshaft, bearings, pressure test* 100
foreseeable future. The carburetor chapter in the
4 Sealing rings, pressure test* 60
service manual for models FS 86 and 106 can be
used as a reference until the new handbook is
5 Crankcase leakage test,
published.
test run 30
6 Cylinder, piston, pressure test* 45
8.1 Repair times
7 Ignition system* 15
The specified repair times assume that the work is
8 Fuel supply, tank vent,
performed by trained personnel in a properly test run 10
equipped service workshop.
9 Manifold or flange,
The repair times are given in minutes. pressure test -
10
Carburetor, check* 25
Note: This table for the new brushcutters
11 Bike handle and throttle control 10
can be added to the STIHL repair times table.
12 Rewind starter, test run 15
13 Clutch, test run 20
14 Muffler 10
15 Air filter 5
16 Stop switch, test run 10
17 Clutch housing 20
18 Drive tube 25
19 Replace complete gearhead
or bearing housing 5
20 Limit stop or deflector 10
21 Drive shaft 15
22 Fuel tank 15
* Test run under load
✂
Waiblingen, December 14, 1994 Andreas Stihl
D1/MTK-na Technical Documentation 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.