Technical Information · issue 14 of 1998
FS 25, FS 65-4: New Brushcutters with 4-Stroke Eng
Models FS 25-4 and FS 65-4 are new brushcutters The new brushcutters are available with
IssueTI 14/1998
Full text
Page 1 of 8
Text of page 1 — search, copy, screen readers
Technical Information
14.98
New STIHL FS 25-4, 65-4 Brushcutters - Series 4170
Models FS 25-4 and FS 65-4 are new brushcutters The new brushcutters are available with
with 22cc and 31cc four-stroke engines designed • Loop handle with or without barrier bar
for occasional users, landscape gardeners, local • Bike handle
governments and farmers.
Typical applications are:
The new 4-stroke engines have a pleasant sound
pattern and are relatively quiet.
• Trimming and cutting weeds and reed
• Cutting wild growth, schrubs and bushes
A new lubrication system permits all-position • Thinning woody scrub, hedges and brushwood
operation of the kind that is self-understood with
STIHL 2-stroke engines.
The shaft and gearhead are from the FS 85. Page 2 of 8
Text of page 2 — search, copy, screen readers
14.98 - 2
Contents
1. Technical description 4. Special accessories for user
2. Specifications 5. Accessories for service
3. Cutting tools 6. Repairs
1. Technical description
1.1 Engine
1.1.1 Weight and size
The weight and overall size of the STIHL single
cylinder 4-stroke engine have been optimized in
the compact design concept.
1.1.2 Construction
• Cylinder and crankcase form a single unit
which has been split along the crankshaft
longitudinal axis.
• The piston features a special wear-resistant
coating.
235TI004 BL Page 3 of 8
Text of page 3 — search, copy, screen readers
14.98 - 3
1.1.3 Valve timing gear, gas flow
6
• Overhead valves (OHV),
one exhaust valve (1), one inlet valve (2) 2 5
• Valve timing via 1
polymer cam (3), cam follower (4), pushrod (5)
and rocker arm (6).
• Cross-flow head (inlet and exhaust opposite 4
one another)
235TI003 BL
1.1.4 Engine lubrication with centrifugal pump: fo
The oil slinger plate (2) is press-fitted on the
crankshaft (1) and produces an oil mist in the oil
tank (3) which is pumped to the lubricating points
by the upward and downward movement of the
piston.
The diaphragm valve (4) controls the flow direction
of the oil mist in two phases:
1. Piston moves downwards:
This causes the pressure in the crankcase to 2
increase and open the diaphragm valve (4). 1
The oil mist is thus pumped to all the lubricating
points of the crankshaft and valve timing gear.
2. Piston moves upwards:
This creates a depression in the crankcase 6
and closes the diaphragm valve (4). 3
The oil mist is now sucked through the return
235TI002 BL
oilways and back to the oil tank. 5 7 4
What prevents oil getting into the crank
chamber and return oilways when the Arrows show flow direction of oil mist
engine is stopped?
The bore (5) in the crankshaft, through which the
oil mist flows to the crankcase, and the end of the
return pipe (6) are located in the center of the oil
tank, i.e. they are always above the oil level -
regardless of the machine’s angle.
This means that the oil remains in the tank in every
engine position. Oil can only flow into the system
when it is atomized by the rotating slinger plate on
the crankshaft. Page 4 of 8
Text of page 4 — search, copy, screen readers
14.98 - 4
1.1.5 Decompression system in timing cam
3 1
235TI005 BL
At cranking RPM, the decompression cam (1) extends the valve opening times. This reduces the
compression pressure and, consequently, the effort required to pull the starter rope. Spring (3) holds the
lever (2) against stop. fo
3 1
235TI006 BL
When the engine reaches idle speed, the decompression cam (1) is pulled back into the timing cam by the
centrifugal force acting on lever (2); the engine then runs with normal valve timing.
1.2 Other features
Carburetor Air filter
• All position diaphragm carburetor with • Foam air filter, impregnated with oil
integral fuel pump
• Additional manual fuel pump for priming Clutch
carburetor before start • Two clutch shoes
• Idle adjusting screw
Drive shaft
Fuel system • Rigid shaft in drive tube
• Transparent tank makes checking fuel level
easier Page 5 of 8
Text of page 5 — search, copy, screen readers
14.98 - 5
1.3 Controls
• Multi-function handle with soft, non-slip grip
surface
2. Specifications
Engine
FS 25-4 FS 65-4
Displacement (cm3) 22.2 31
Bore (mm) 33 39
Stroke (mm) 26 26
Engine power to ISO 8893: 0.6 kW 0.85 kW
(0.8 bhp) (1.2 bhp)
Max. engine speed: 11,500 rpm
Max. speed of output shaft
(tool mounting): 9,300 rpm
Idling speed: 3,100 rpm
Clutch engages at 4,200 rpm
Valve clearance with engine cold:
Inlet 0.1 - 0.14 mm
Exhaust fo
0.13 - 0.17 mm
Noise, vibration
Model Tool Sound Sound power Vibration measurement Vibration measurement
pressure level Lweq to to ISO 7916, to ISO 7916,
level Lpeq to ISO 108841) Idle speed (m/s2) Max. RPM (m/s2)
ISO 7917 1) Handle Handle
dB(A) dB(A) right left right left
FS 25-4 2) Nylon head 88 101 2.3 2.6 4.4 4.3
FS 25-4 2) Metal tool 89 98 2.3 2.6 3.6 3.5
FS 25-4 R 3) Nylon head 89 101 2.0 2.3 7.4 5.4
FS 25-4 R 4) Metal tool 90 98 2.0 2.3 11.0 5.8
FS 65-4 2) Nylon head 92 103 0.9 1.4 3.8 3.9
FS 65-4 2) Metal tool 92 102 0.9 1.4 3.6 3.8
FS 65-4 R 3) Nylon head 91 102 1.7 2.3 9.1 6.1
FS 65-4 R 4) Metal tool 91 100 1.7 2.3 10.7 6.0
1)
Weighted equivalent level includes idling and racing with the same duration of exposure
2)
Bike handle version
3)
Loop handle version
4)
Loop handle version with barrier bar
Engine lubrication: Weight
Multigrade oil SAE 15 W 40 without cutting tool and deflector:
Class SG or SF
Capacity max. 100 ml FS 25-4 with loop handle 6.2 kg
FS 25-4 with bike handle 6.4 kg
Fuel tank capacity: FS 65-4 with loop handle 6.4 kg
FS 25-4 0.45 l (450 cm3) FS 65-4 with bike handle 6.6 kg
FS 65-4 0.65 l (650 cm3) Page 6 of 8
Text of page 6 — search, copy, screen readers
14.98 - 6
3. Cutting tools
The following cutting tools are approved:
1 2
1 STIHL Supercut 20-2
4002 710 2162
681FK003
2 STIHL Autocut 21-2
4002 710 2113
3 STIHL Autocut 25-2
4002 710 2108 4
3
4 STIHL Autocut 30-2 1)
4002 710 2107
5 STIHL Polymatic 30-2
681FK007
4002 710 2120
6 STIHL Polycut 20-3
4002 710 2130
7 Cutting blade 230-4 2)
4001 713 3801 5 6
8 Cutting blade 230-8 2)
4001 713 3803
9 Brush knife 250-3 2)
4112 713 4100
10 Circular saw blade 200 (scratcher tooth) 3)
4112 713 4201
11 Circular saw blade 200 (chisel tooth) 3)
7 fo 8
4112 713 4203
1)
Note for FS 25-4
2)
Not for loop handle units without barrier bar
3) 10
Only for FS 65-4 with bike handle 9
4. Special accessories for users
Part Name Part No. Application, Remarks
Transport guard for 4116 790 3900 For all metal cutting tools
metal cutting tools 4119 790 3906 Cutting blade 230-4, 255-8,
circular saw blade 225 (scratcher and chisel tooth)
4119 790 3901 Circular saw blade 200 and 225 (scratcher and
chisel tooth)
STIHL gear lubricant
- 80 g tube 0781 120 1109 Drive shaft in drive tube
- 225 g tube 0781 120 1110
STIHL heavy-duty gear lubricant
- 80 g tube 0781 120 1117 Gearhead
- 225 g tube 0781 120 1118
STIHL special oil Rewind spring in starter,
- 100 ml bottle 0781 417 1315 bearing bore in rope rotor Page 7 of 8
Text of page 7 — search, copy, screen readers
14.98 - 7
4.1 Nylon line for cutting heads
Line diameter For use with
/ color
2.4 mm / orange Supercut 20-2, Autocut 21-2, Autocut 25-2, Autocut 30-2,
Polymatic 30-2, Polycut 20-3
2.7 mm / red Polycut 20-3
4.2 Sharpening aids for metal cutting tools
Part Name Part No. Application
Saw set 4020 893 5000 Circular saw blade 200 and 225 (chisel tooth)
Sharpening template 4020 890 5500 Brush knife
5. Service accessories
Special servicing tools are listed in the service
manual for models FS 25-4, 65-4.
Other available tools are a locking screw for
blocking the crankshaft and an installing tool for
the piston.
It consists of
Press arbor
235TI007 GM
Press sleeve 8 x 31 (FS 25-4)
Press sleeve 8 x 29.5 (FS 65-4)
Piston support
Locking screw 4170 893 1200 for piston
6. Repairs
A service manual is available for servicing and repair procedures on the FS 25-4, 65-4.
The service manual does not include the chapters "Servicing the Carburetor", "Troubleshooting" or
any repairs involving standard procedures. Such repairs are described in separate handbooks.
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.
6.1 Installed position of piston
1
Arrow (1) on piston crown must point to inlet side
235TI010 BL Page 8 of 8
Text of page 8 — search, copy, screen readers
14.98 - 8
6.2 Repair times
No. Repair procedure FS 25-4
FS 65-4
The specified repair times assume that the work
is performed by trained personnel in a properly 1 Remove and refit engine 15
equipped service workshop.
2 Crankcase, pressure test* ---
The repair times are given in minutes.
3 Crankshaft, bearings, pressure
Note: This table for the new brushcutters test* ---
can be added to the STIHL repair times table.
4 Sealing rings, pressure test* ---
5 Crankcase leakage test,
test run ---
6 Cylinder, piston, pressure test* ---
7 Ignition system, contact* 15
8 Fuel supply, tank vent, test run 10
9 Manifold or flange, pressure test ---
10 Carburetor, check* 25
11 fo
Bike handle and throttle control 10
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 gearhead or
bearing housing 5
20 Limit stop or deflector 10
21 Drive shaft 15
22 Fuel tank 5
23 Check compression pressure 5
24 Adjust valve clearance 20
25 Replace crankcase, bottom half 100
26 Replace crankshaft 100
27 Replace cylinder, piston 120
* test run under load ✂
1998 Andreas Stihl Andreas Stihl - D1/MTK-st
Technical Documentation 6276 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.