Stihl TS 420 User manual

STIH)
STIHL TS 410, 420 2007-09

1TS 410, TS 420
q
© ANDREAS STIHL AG & Co. KG, 2007
RA_370_00_01_03
1. Introduction 3
2. Safety precautions 5
3. Specifications 6
3.1 Shortblock 6
3.2 Fuel system 6
3.3 Ignition system 6
3.4 Cutting wheels 6
3.5 Tightening torques 7
4. Troubleshooting 9
4.1 Clutch 9
4.2 Cast arm with guard 10
4.3 Rewind starter 11
4.4 Ignition system 12
4.5 Carburetor 14
4.6 Engine 17
5. Cast arm with guard 18
5.1 Water system 18
5.2 Cast arm with guard 19
5.3 Testing radial and axial
truth of running 24
5.4 Test sequence 25
5.5 Ribbed poly V-belt 26
5.6 Tensioner 27
5.7 Starter cup 28
6. Clutch 30
6.1 Belt pulley /
clutch drum 31
6.2 Studs for securing the
cast arm with guard 32
7. Shortblock 33
7.1 Muffler / spark arresting
screen 33
7.2 Leak testing 34
7.2.1 Preparatory steps 34
7.2.2 Vacuum test 34
7.2.3 Pressure test 35
7.3 Oil seals 36
7.4 Removing and installing
the shroud 37
7.5 Cylinder 39
7.6 Crankshaft 41
7.6.1 Removal and
installation 41
7.6.2 Grooved ball
bearing / crankcase 46
7.7 Piston 47
7.7.1 Removal 47
7.7.2 Installation 48
7.8 Piston rings 50
7.9 Decompression valve 50
8. Ignition system 51
8.1 Ignition module 51
8.1.1 Removal and
installation 51
8.2 Ignition timing 53
8.3 Testing the ignition
module 53
8.4 Spark plug boot 54
8.5 Flywheel 55
8.6 Short circuit wire /
switch 56
8.6.1 Testing 56
8.6.2 Removal and
installation 56
8.7 Troubleshooting,
ignition system 58
9. Rewind starter 61
9.1 General 61
9.2 Removal and
installation 61
9.3 Pawl 61
9.4 Rope rotor 62
9.5 Starter rope /
starter grip 63
9.6 Tensioning the rewind
spring 64
9.7 Replacing the rewind
spring 65
10. Repairing the
AV system 67
10.1 AV spring on the
handlebar 67
10.2 AV spring in the
support 68
10.3 AV spring at the bottom
of the crankcase 68
10.4 AV spring on the
carburetor 69
10.5 Handlebar 69
10.6 Rubber buffers /
support 71
11. Actuating levers 73
11.1 Switch shaft /
choke lever 73
11.1.1 Switch shaft, removal
and installation 73
11.2 Throttle trigger /
trigger interlock, removal
and installation 74
11.2.1 Choke lever / holder,
removal and
installation 76
Contents

2TS 410, TS 420
Contents
12. Fuel system 77
12.1 Air filter 77
12.2 Carburetor, removal and
installation 77
12.2.1 Leakage testing 79
12.3 Repairing the
carburetor 79
12.3.1 Metering diaphragm 79
12.3.2 Inlet needle 80
12.3.3 Fixed jet 81
12.3.4 Pump diaphragm 81
12.3.5 Air valve 83
12.3.6 Choke shaft /
choke shutter 85
12.3.7 Throttle shaft /
throttle shutter 87
12.3.8 Adjusting screws 89
12.4 Carburetor adjustment 90
12.4.1 Basic setting 90
12.4.2 Standard setting 91
12.5 Choke rod and
throttle rod 92
12.6 Intake elbow, removal
and installation 93
12.6.1 Impulse hose 94
12.7 Tank vent 95
12.7.1 Testing 95
12.7.2 Removal and
installation 96
12.7.3 Manual fuel pump 96
12.8 Fuel Intake 97
12.8.1 Pickup body 97
12.8.2 Fuel hoses 98
12.8.3 Fuel tank filler cap 99
12.9 Tank housing, removal
and installation 99
13. Special tools 101
14. Servicing
accessories 103

3TS 410, TS 420
1. Introduction
This service manual contains
detailed descriptions of all the
typical repair and servicing
procedures for this power tool.
Refer to the illustrated spare parts
lists during all repair work. These
lists show the installation position
and order in which the individual
parts and modules should be
assembled.
Refer to the latest edition of the
relevant parts list to check the part
numbers of any replacement parts
required.
A fault on the machine may be due
to several causes. To help locate
the fault, consult the chapter on
"Troubleshooting" and the
"STIHL Service Training System"
for all function groups.
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 and
service manual until an updated
edition is issued.
The special tools mentioned in the
descriptions are listed in the chapter
"Special Servicing Tools" of this
manual. Use the part numbers to
identify the tools in the STIHL
Special Tools manual.
It lists all the special servicing tools
currently available from STIHL.
Symbols are included in the text and
pictures for greater clarity.
The meanings are as follows:
In the text:
:= Action to be taken as shown in
the illustration above the text
– = Action to be taken but not
shown in the illustration above
the text
In the illustrations:
AItem pointer (short arrow)
aDirection of movement
(long arrow)
b4.2 = Reference to another
chapter, i.e. to chapter 4.2
in this case
Service manuals and technical
information bulletins are intended
exclusively for the use of properly
equipped repair shops. They must
not be passed on to third parties.
Servicing and repairs are made
considerably easier by mounting the
machine on the assembly stand (3)
5910 890 3100. For this purpose,
secure the support (2)
5910 850 1650 to the assembly
stand with two screws (1) and
washers.
The screws must not protrude, as
they may damage the housing when
the machine is clamped, depending
on model.
This step is not necessary when
using the new assembly stand
5910 890 3101, as the support is
already mounted on it.
The clamping plate (1)
4238 890 2100 is secured to
the support (2) with two M8x20
screws (3) and washers.
1
2
3
219RA000 TG
3
12
3
370RA000 TG

4TS 410, TS 420
The machine is secured to the
clamping plate by means of the two
front studs on the crankcase.
Guide the studs on the machine
through the bushings on the
clamping plate and secure them
with the nuts (arrows).
The cast arm with guard must be
removed first.
Always use original STIHL
replacement parts.
They can be identified by the STIHL
part number, the STIH) logo
and the parts symbol (
The symbol may appear alone on
small parts.
Storage and disposal of oil and
fuel
Lubricating oil and fuel must be
collected in a clean container and
disposed of in accordance with the
regulations and without harming the
environment.
370RA001 TG

5TS 410, TS 420
2. Safety precautions
Specific national safety regulations
and the safety instructions in the
instruction manual must be
observed if the machine has to be
started up during maintenance or
repair work.
Gasoline is highly inflammable and
can also be explosive under certain
conditions.
Protective gloves must be worn
when components have to be
heated for assembly/removal
purposes.
Improper handling may result in
burns and other serious injuries.
Do not bring any fire, flame, spark or
other source of heat near the fuel.
All work with fuel must be performed
outdoors only. Spilled fuel must be
wiped away immediately.
Always test for leaks after working
on the fuel system and shortblock.

6TS 410, TS 420
3. Specifications
3.1 Shortblock
TS 410 TS 420
Displacement: 66.7 cm366.7 cm3
Bore: 50 mm 50 mm
Stroke: 34 mm 34 mm
Engine power to ISO 7293: 3.2 kW (4.4 HP)
at 9000 rpm
3.2 kW (4.4 HP)
at 9000 rpm
Permissible maximum speed: 10300 rpm 10300 rpm
Idle speed: 2500 rpm 2500 rpm
Clutch: Centrifugal clutch without
linings
Clutch engages at: 3800 rpm 3800 rpm
Crankcase leakage test
at gauge pressure: pü= 0.5 bar
under vacuum pu= 0.5 bar
3.2 Fuel system Carburetor leakage test at
gauge pressure: pü= 0.8 bar
Operation of tank vent at
gauge pressure: pü= 0.3 bar
Fuel: as specified in instruction
manual
3.3 Ignition system Air gap between ignition
module and flywheel: 0.15...0.35 mm
Spark plug (suppressed): Bosch WSR6F
Electrode gap: 0.5 mm
3.4 Cutting wheels
TS 410
Composite and diamond cutting wheels Diameter 300 mm
Cutting depth approx. 100 mm
TS 420
Composite and diamond cutting wheels Diameter 350 mm
Cutting depth approx. 125 mm

7TS 410, TS 420
3.5 Tightening torques
DG and P screws are fitted in plastic and light alloy metal parts. These screws form a permanent thread when
they are installed for the first time. The material is permanently deformed. Screws can be removed and installed
as often as necessary without impairing the strength of the screwed assembly, provided that the specified
tightening torque is observed.
For this reason, it is essential to use a torque wrench.
Fastener Thread size For component Tightening
torque
Remarks
Nm
Bolt M 6x28 Cast arm / flange 8.0
Nut M 8 Cast arm/starter cover/stud 20.0
M 10x1 Decompression valve 14.0
Bolt M 5x20 Filter cover / tank housing 6.0
Bolt P 5x16 Handle molding / shroud 4.0
Bolt D 5x20 Rubber buffer / support 6.0
Bolt P 5x16 Holder / switch / shroud 3.0
Bolt P 6x19 Holder / water attachment / tank housing 6.0
Bolt P 6x19 Shroud / tank housing 6.0
Bolt M 5x17 Cap, spark plug cover / shroud 3.5
Nut M 10x1 L Poly V-belt pulley, front 38.0
Bolt P 6x40 Clamp / handlebar / tank housing 6.0
Bolt P 6x26 Clamp / tank housing 6.0
Bolt D 5x45 Clamp (AV system) /handlebar support 4.0
Bolt P 6x19 Crankcase / bearing plug (AV system) 6.0
Bolt M 5x32 Crankcase / cylinder 9.0
Bolt M 5x25 Crankcase fan side/ drive side 10.0
M 12x1 L Driver 40.0
Bolt M 5x6 Bearing / rubber buffer 4.0 1)
Bolt P 5x16 Bearing plug AV system /tank housing 4.0
Bolt M 5x20 Fan cover / crankcase 6.0
Bolt P 6x19 Air baffle / tank housing 6.0
Bolt M 5x20 Air guide shroud / crankcase 3.0
Bolt M 5x20 Muffler /crankcase 10.0
Bolt M 5x20 Muffler / cylinder 10.0
Bolt M 5x30 Belt guard / cast arm 6.0
Nut M 8x1 Flywheel/ crankshaft 33.0 2)
Bolt D 5x24 Clamping lever/cast arm 4.0
Bolt M 3x20 Hose clamp, manifold / cylinder 0.5
Nut M 8x1 Starter cup / crankshaft 33.0
Bolt M 8x53 Stud / crankcase 21.0
Bolt P 6x50 Support / clamp / handlebar / tank
housing
6.0

8TS 410, TS 420
Bolt P 6x19 Support / bearing plug AV system 6.0
Bolt P 6x40 Support / tank housing 6.0
Bolt M 5x48x22 Tank housing / flange 3.5
Bolt M 10x18 Abrasive wheel 30.0
Bolt M 5x30 Adjusting lever / guard 6.0
Bolt M 8x24 Adjusting lever / guard/ square nut, drive
side
3.0
Bolt M 8x17 Adjusting lever / guard/ square nut, fan
side
3.0
M 14x1.25 Spark plug 28.0
Bolt M 5x20 Ignition module / crankcase 8.0
Bolt M 4x8 Pan head screw / banjo bolt 3.0
Remarks:
1) Loctite 243 medium strength
2) Connection between crankshaft and flywheel must be degreased and oil-free
When inserting DG and P screws into an existing screw thread:
Insert the DG or P screw in the hole and turn counterclockwise until it gently drops into the hole in axial
direction.
Tighten the screw clockwise to the specified torque.
DG screws must always be tightened with a torque wrench.
This procedure ensures that the screw engages properly in the existing thread and does not form a new thread
and weaken the assembly.
Coat micro-encapsulated screws with Loctite 243 medium strength before refitting them.
Screwdriver speed when used in plastic material: DG and P screws max. 500 rpm.
Do not use an impact wrench to release or tighten screw connections.
Screws with and without locking serration must not be confused.

9TS 410, TS 420
4. Troubleshooting
4.1 Clutch
Problem Cause Remedy
Cutting wheel stops under load
at full throttle
Clutch shoes badly worn Install new clutch
Clutch drum badly worn Install new clutch drum
Cutting wheel rotates at idle speed Idle speed too high Readjust with idle speed screw LA
(counterclockwise)
Clutch springs stretched or fatigued Replace tension springs, replace
clutch if necessary
Clutch spring hooks broken Replace tension springs
Loud noises Clutch springs stretched or fatigued Replace all tension springs
Grooved ball bearing on poly V-belt
pulley /clutch drum damaged
Replace grooved ball bearing
Clutch shoe retainer broken Replace retainer
Clutch shoes and carrier worn Install new clutch

10 TS 410, TS 420
4.2 Cast arm with guard
Problem Cause Remedy
Cutting wheel does not run
smoothly or vibrates
Axial or radial runout Set axial or radial true running,
replace cutting wheel if necessary
Ribbed poly V-belt is loose Check and tension ribbed poly
V-belt, replace ribbed poly V-belt or
tensioner if necessary
Grooved ball bearing of the front
poly V-belt pulley is worn
Replace grooved ball bearing
Cutting wheel stops under load
at full throttle
Clutch shoes badly worn Install new clutch
Clutch drum badly worn Install new clutch drum
Ribbed poly V-belt not properly
tensioned
Tension ribbed poly V-belt, replace
if necessary
Cutting wheel rotates at idle speed Idle speed too high Readjust with idle speed screw LA
(counterclockwise)
Clutch springs stretched or fatigued Replace tension springs, replace
clutch if necessary
Clutch spring hooks broken Replace tension springs
Cutting wheel runs dry although
shutoff cock is open
Shut-off cock or connector for hose
is clogged
Check and clean shut-off cock/
connector, replace if necessary
Nozzles are clogged Clean nozzles, replace if necessary

11TS 410, TS 420
4.3 Rewind starter
Problem Cause Remedy
Starter rope broken Rope pulled out too vigorously as
far as stop or over edge, i.e. not
vertically
Replace starter rope
Normal wear Replace starter rope
Starter rope does not rewind Very dirty or corroded Clean or replace rewind spring
Spring insufficiently tensioned Check rewind spring and increase
tension
Rewind spring broken Replace rewind spring
Starter rope cannot be pulled out
far enough
Rewind spring overtensioned Check rewind spring and reduce
tension
Starter rope can be pulled out
almost without resistance
(crankshaft does not turn)
Guide peg on pawls or pawls
themselves are worn
Replace pawls
Spring clip fatigued Replace spring clip
Loose starter cup Tighten starter cup, replace if
necessary
Starter rope is difficult to pull or
rewinds very slowly
Starter mechanism is very dirty 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 little
standard solvent-based degreasant
(containing no chlorinated or
halogenated hydrocarbons), then
pull rope carefully several times
until normal action is restored

12 TS 410, TS 420
4.4 Ignition system
Exercise extreme caution while
carrying out maintenance and
repair work on the ignition system.
The high voltages which occur can
cause serious or fatal accidents.
Problem Cause Remedy
Engine runs roughly, misfires,
temporary loss of power
Spark plug boot is loose Press boot firmly onto spark plug
and fit new spring if necessary
Spark plug sooted, smeared with oil Clean the spark plug or replace if
necessary
Ignition lead loose in ignition
module
Secure ignition lead
Fuel/oil mixture contains too much
oil
Use a fuel mixture with the correct
mixing ratio
Incorrect air gap between ignition
module and flywheel
Set the correct air gap
Flywheel cracked
or has other damage or pole shoes
have turned blue
Install new flywheel
Ignition timing wrong, flywheel out
of adjustment, key in flywheel has
sheared off
Install new flywheel
Weak magnetization in flywheel –
pole shoes have turned blue
Install new flywheel
Irregular spark Check operation of switch shaft /
contact spring, switch and ignition
module
Insulation damaged or break in
ignition lead or short circuit wire,
check ignition lead / ignition module,
replace if necessary
Check operation of spark plug
Clean the spark plug or replace if
necessary
If the engine runs roughly, this may also be due to problems in the carburetor or shortblock.

13TS 410, TS 420
Problem Cause Remedy
No spark Spark plug defective Replace spark plug
Faulty insulation or short circuit in
short circuit wire or short circuit
switch
Check short circuit wire and switch,
replace switch if necessary
Break or damaged insulation in
ignition lead
Check ignition lead, replace if
necessary
Ignition module defective Replace ignition module

14 TS 410, TS 420
4.5 Carburetor
Problem Cause Remedy
Carburetor floods; engine stalls Inlet needle not sealing.
Foreign matter in valve seat or
cone
Remove and clean inlet needle or
clean carburetor
Inlet control lever sticking on
spindle
Restore easy movement of inlet
control lever
Helical spring not located on nipple
of inlet control lever
Remove the inlet control lever and
refit it correctly
Perforated disc on diaphragm is
deformed and presses constantly
against the inlet control lever
Replace metering diaphragm
Poor acceleration Low speed adjusting screw
"too lean"
Check basic setting of carburetor,
correct if necessary
High speed adjusting screw
"too lean"
Check basic setting of carburetor,
correct if necessary
Inlet needle sticking to valve seat Remove inlet needle, clean and
refit
Diaphragm gasket leaking Replace diaphragm gasket
Metering diaphragm damaged or
shrunk
Replace metering diaphragm
Manifold damaged Replace manifold
Impulse hose damaged or kinked Straighten or replace impulse hose

15TS 410, TS 420
Problem Cause Remedy
Engine will not idle, idle speed too
high
Throttle shutter opened too wide by
idle speed screw LA
Set idle speed screw LA correctly
Oil seals / crankcase leaking Seal oil seals / crankcase, replace if
necessary
Air valve soiled
– air valve does not close
Clean air valve, replace if
necessary
Air valve moves stiffly Check air valve, replace if
necessary
Throttle rod moves stiffly
– throttle shutter does not close
Restore easy movement of throttle
rod
Engine stops when idling Idle jet bores or ports blocked Clean the carburetor
Low speed adjusting screw "too
rich" or "too lean"
Correct setting of low speed
adjusting screw L
Setting of idle speed screw
incorrect – throttle shutter
completely closed
Correct setting of idle speed
screw LA

16 TS 410, TS 420
Problem Cause Remedy
Engine speed drops quickly under
load – low power
Air filter dirty Replace air filter
Throttle shutter not opened fully Check linkage
Tank vent faulty Replace tank vent
Pickup body soiled Replace pickup body
Fuel strainer dirty Clean fuel strainer in carburetor,
replace if necessary
Leak in fuel line between tank and
fuel pump
Seal connections or replace line
High speed adjusting screw H
"too rich"
Check basic setting of carburetor,
correct if necessary
Main jet bores or ports blocked Clean the carburetor
Pump diaphragm damaged or
fatigued
Replace pump diaphragm
Impulse hose damaged or kinked Straighten or replace impulse hose
Engine runs extremely richly, lacks
power and has very low final speed
Air valve does not open Check lever and rod on air valve,
adjust or replace if necessary
Engine runs too richly, loses power,
final speed is too low
Air valve does not open completely
at full throttle
Lever on air valve has been fitted
incorrectly – the stamped number
must not be visible
Check lever, rod and air valve,
adjust, clean or replace if
necessary
Engine idles erratically – too lean Air valve does not close completely Check lever, rod and air valve,
adjust, clean or replace if
necessary

17TS 410, TS 420
4.6 Engine
Always check and, if necessary,
repair the following parts before
looking for faults on the engine:
- Air filter
- Fuel supply
- Carburetor
- Ignition system
Problem Cause Remedy
Engine does not start easily, stalls
at idle speed but operates normally
at full throttle
Oil seals in crankgear damaged Replace oil seals
Crankcase leaking or damaged
(cracks)
Seal / replace crankcase
Engine does not deliver full power
or runs erratically
Piston rings worn or broken Replace piston rings
Muffler /spark arresting screen
carbonized
Clean muffler (inlet and outlet
openings), replace spark arresting
screen, replace muffler if necessary
Air filter dirty Replace air filter
Fuel/ impulse hose severely bent,
kinked or damaged
Fit new lines and ensure they are
installed without kinking
Tank vent faulty Check tank vent and replace if
necessary
Air valve does not open Check air valve, adjust or replace if
necessary
Decompression valve does not
close
Replace decompression valve
Engine overheating Insufficient cylinder cooling.
Air inlet openings in fan cover
clogged or cooling fins on cylinder
severely fouled.
Thoroughly clean all cooling air
openings and the cylinder fins.

18 TS 410, TS 420
5. Cast arm with guard
5.1 Water system
Nozzles
:Take out banjo bolts (arrow) on
both sides – the square nuts
inside the guard drop down.
– Disconnect and examine the
hose (1), fit a new hose if
necessary.
:Remove screw (1)
:Guide the adjusting lever (2) over
the lift-off lugs (arrow) with a
gentle turning movement and
remove it.
When fitting the adjusting lever, it is
simply pushed into place until it
engages.
– Insert and tighten down the
screw.
– Tightening torques, b3.5.
1
370RA003 TG370RA004 TG
21
Fit the square nut (1) in the guides
(arrows) inside the guard and hold
it.
– Fit the connector (1) with water
hose and align it at 90° to the
adjusting lever (2).
:Insert the banjo bolt (3) and
screw it tight.
– Examine the sealing ring on the
banjo bolt and replace it if
necessary.
– STIHL Press Fluid makes it
easier to fit the sealing rings,
b14.
– Fit the square nut on the inside of
the guard and slide the banjo bolt
through the hole in the adjusting
lever from the other side with
gasket and sealing ring.
– Insert the banjo bolt and screw
it tight.
370RA006 TG
1
90°
1
370RA043 TG
2
3
Water attachment
:Apply a screwdriver to the hose
clip (arrow) and turn slightly to
open the clip.
– Pull off the hose (1).
– Open the hose clip and remove
the hose.
:Insert a hexagon socket head
wrench (3) in the connector
(arrow) and turn the connector
down.
– Take the shut-off cock (1) from
the holder (2) and examine it; fit a
new part if necessary.
370RA007 TG
1
2
1 3
370RA008 TG

19TS 410, TS 420
– Examine the holder (1) and
replace it if necessary.
:Take out the screw (arrow)
underneath the machine.
– Remove the holder (1).
– Reassemble parts in reverse
order.
:Press the tabs (arrows) on the
hose clip (1) together until it
engages.
– Assemble remaining parts in
reverse order.
370RA012 TG
1
370RA009 TG
1
5.2 Cast arm with guard
:Unscrew collar nuts (arrows).
:Relax the ribbed poly V-belt by
turning the hexagon (1) on the
tensioner counterclockwise until
the arrow points to "0" (arrow).
– Take out the banjo bolt on the
guard and remove the connector
with water hose.
:Take the hose (1) out of the
guides (arrows).
370RA010 TG370RA011 TG
1
370RA013 TG
1
:Remove the screw (arrow).
:Remove the belt guard (1).
:Take out the collar nuts (arrows).
– Remove starter cover (1).
– Remove the ribbed poly V-belt,
b5.5.
:Remove the cast arm with
guard (1).
370RA014 TG
1
370RA274 TG
1
370RA017 TG
1