Echo SRM-420ES (L): SRM-420ES (U) Mounting instructions

SRM-420ES
10-42A-00 1
INTRODUCTION
We are constantly working on technical im-
provement of our products. For this reason,
technical data, equipment and design are
subject to change without notice. All speci-
fications and directions in this SERVICE
DATA are based on the latest product infor-
mation available at the time of publication.
1
SERVICE DATA
TRIMMER/BRUSHCUTTER
ECHO:
SRM-420ES
STAGE MODEL
(Serial number : 37000001 and after)
CONTENTS
page
1 SERVICE INFORMATION.............................. 2
1-1 Specification ............................................... 2
1-2 Technical data............................................. 3
1-3 Torque limits................................................ 4
1-4 Special repairing materials ......................... 4
1-5 Service limits............................................... 5
1-6 Special tools ............................................... 6
2 CARBURETTOR ADJUSTMENT PROCEDURE
.. 7
2-1 General adjusting rules............................... 7
2-2 Presetting Idle adjust screw, L mixture
needle
and H mixture needle
.......................................... 7
2-3 Adjusting carburettor................................... 8
Reference No. 10-42A-00
ISSUED: 201204

SERVICE INFORMATION SRM-420ES
2
1 SERVICE INFORMATION
1-1 Specifications
Model SRM-420ES (L) SRM-420ES (U)
Dimentions* Length mm (in) 1840 (72.4)
Width mm (in) 355 (14.0) 680 (26.8)
Heigh mm (in) 287 (11.3) 510 (20.1)
Dry weight* kg (lb) 8.3 (18.2) 8.8 (19.3)
Engine Type YAMABIKO, air-cooled, two-stroke, single cylinder
Rotation Anticlockwise as viewed from the output end
Displacement cm3 (in3) 41.5 (2.53)
Bore mm (in) 40.0 (1.58)
Stroke mm (in) 33.0 (1.30)
Compression ratio 6.7
Carburettor Type Rotary type : Diaphragm, horizontal-draught, with primer
Model WALBRO WT-1046
Ignition Type CDI (Capacitor discharge ignition) system
Digital magneto
Spark plug BPMR8Y
Exhaust Muffler type Spark arrester muffler with catalyst
Starter Type ES (effortless-start)
Rope diameter x length mm (in) 3.8 x 910 (0.15 x 35.9)
Fuel** Type Premixed two-stroke fuel
Mixture ratio 50 : 1 (2%)
Petrol Minimum 89 octane
Two-stroke engine oil ISO-L-EGD (ISO/CD13738), JASO FC/FD
Tank capacity L (U.S.fl.oz.) 0.68 (23.0)
Clutch Type Centrifugal, 2-shoe pivot
Handle Type
Front : Crescent loop with cushion grip
U-handle with integrated
control grip
Rear : Integrated control grip with cushion
Drive shaft Type Solid type with serration (10-tooth)
Diameter - Length mm (in) 8.0 - 1588 (0.31 - 62.52)
Housing OD - ID mm (in) 28.0 - 24.0 (1.10 - 0.94)
Main pipe Length mm (in) 1537 (60.5)
Gear case Reduction ratio 1.33
Gear tooth Spiral bevel gear
Lubrication Lithium based grease or ECHO XTended Protection TM Lubricant
Cutter Type Nylon line cutter 3-tooth blade (255 mm)
Arbor diameter for blade mm (in) 25.4 (1.0)
Fastener type, size mm Left-hand thread nut, M10 x 1.25 pitch
Cutting rotation Anticlockwise as viewed from top
OD: Outer diameter. ID: Inner diameter. * Without shoulder harness and standard cutter.
** Refer to Operator’s manual.

SERVICE INFORMATIONSRM-420ES 3
1-2 Technical data
Model SRM-420ES (L) SRM-420ES (U)
Engine
Idling speed r/min 2,800 +/- 400
Wide open throttle speed r/min 9,500 - 10,500* 10,500 - 11,500**
Clutch engagement speed r/min 3,700
Engagement Limit†r/min Less 3,300 or over 4,300
Compression pressure MPa (kgf/cm2) (psi) 0.92 (9.4) (132)
Ignition system with stop holding function
Spark plug gap mm(in) 0.6 - 0.7 (0.024 - 0.028)
Minimum secondary voltage at 1500 r/min kV 22
Primary coil resistance MΩ2.4 -2.9
(Red Probe on stop terminal of module)
Secondary coil resistance Ω930 - 970
Pole shoe air gaps mm(in) 0.3 - 0.4 (0.012 - 0.016)
Ignition timing at 3,000 r/min °BTDC 12
at 8,000 r/min °BTDC 25
at 10,000 r/min °BTDC 23
Carburettor
Venturi Size 12.7 (0.50)
Throttle Bore 14.3 (0.56)
Idle adjust screw initial setting turns in*** 2 1/8
L mixture needle initial setting turns out 2 3/8
H mixture needle initial setting turns out 3
Test Pressure, minimum MPa (kgf/cm2) (psi) 0.05 (0.5) (7.0)
Metering lever height mm(in) 1.65 (0.06) lower than diaphragm seat
BTDC: Before top dead centre.
*With Nylon line cutter and shield.
**With 3-tooth blade (255 mm).
*** Set idle adjust screw to the point that its tip just contacts throttle plate before initial setting.
†If clutch engagement speed is lower than lower service limit speed or higher than uper service limit speed,
replace clutch assembly with new one.

SERVICE INFORMATION SRM-420ES
4
1-3 Torque limits
Descriptions Size kgf•cm N•m in•lbf
Starter Pawl M 8 60 - 90 6 - 9 50 - 80
system Starter case M 5 30 - 45 3 - 4.5 26 - 40
Ignition Magneto rotor (Flywheel) M 8 200 - 240 20 - 24 175 - 210
system Ignition coil M 5 50 - 70 5 - 7 45 - 60
Spark plug M 14 130 - 170 13 - 17 115 - 150
Fan cover M 5 30 - 45 3 - 4.5 26 - 40
Fuel Carburettor M 5 40 - 55 4 - 5.5 35 - 50
system Intake bellows M 5 30 - 50 3 - 5 26 - 45
Intake insulator M 5 50 - 70 5 - 7 45 - 60
Insulator plate M 5 30 - 45 3 - 4.5 26 - 40
Fuel tank bracket M 5 50 - 70 5 - 7 45 - 60
Fuel tank M 5 50 - 70 5 - 7 45 - 60
Clutch Clutch shoe M 6 70 - 110 7 - 11 60 - 95
Engine Crankcase M 5** 70 - 110 7 - 11 60 - 95
Cylinder M 5** 70 - 110 7 - 11 60 - 95
Cylinder cover M 5 20 - 30 2 - 3 17 - 26
Stand M 5 20 - 30 2 - 3 17 - 26
Muffler M 6 100 - 140 10 - 14 90 - 125
Muffler cover M 5* 30 - 45 3 - 4.5 26 - 40
Muffler stay M 5 60 - 90 6 - 9 50 - 80
Others Blade fastening nut LM 10 280 - 320 28 - 32 245 - 280
Regular bolt, nut and screw M 3 6 - 10 0.6 - 1 5 - 9
M 4 15 - 25 1.5 - 2.5 13 - 22
M 5 25 - 45 2.5 - 4.5 22 - 40
M 6 45 - 75 4.5 - 7.5 40 - 65
M 8 110 - 150 11 - 15 95 - 130
M 10 210 - 300 21 - 30 180 - 260
LM: Left hand thread.* Apply thread locking sealant. (See below)
** The torque differences among four bolts should not exceed 20 kgf•cm (2N•m, 17in•lbf) on one cylinder or
crankcase.
1-4 Special repairing materials
Material Location Remarks
Grease Gear case
Rewind spring
Lithium based grease or ECHO XTended Protection
TM
Starter center post Lubricant
Oil Oil seal inner lips Two-stroke engine oil or engine oil (SAE#30)
Drive shaft
Thread locking sealant Muffler cover Loctite #242, ThreeBond #1324 or equivalent

SERVICE INFORMATIONSRM-420ES 5
5K225 5K016 5K042
5K1895K219 5K220
5K246
5K245 5K223 5K2245K222
1-5 Service limits
ABCD
EFGH
KLM
Description mm (in)
A Cylinder bore When plating is worn and aluminum can be seen
BPiston outer diameter Min. 39. 91 (1.571)
CPiston pin bore Max. 10. 035 (0.3951)
DPiston ring groove Max. 1. 6 (0.063)
EPiston ring side clearance Max. 0. 1 (0.004)
FPiston pin outer diameter Min. 9. 98 (0.3929)
GPiston ring width Min. 1. 45 (0.057)
HPiston ring end gap Max. 0. 5 (0.02)
KCon-rod small end bore Max. 13. 025 (0.5128)
LCrankshaft runout Max. 0. 02 (0.001)
MClutch drum bore Max. 71. 5 (2.81)

SERVICE INFORMATION SRM-420ES
6
1.5
1.65
1.3
0.4
a
0
0.4
50
0.8
1.2
1.
MPa
0
a
b
PET-304
1
7
4
3
2
b
Key Part Number Description Used for:
1 G310-000050 Tachometer PET-304 Measuring engine speed to adjust carburettor
2 X605-000050 Torx L wrench Removing and installing bolt
3 897501-03938 Puller Removing flywheel
4 897835-16131 Pressure connector Testing crankcase and cylinder leakages
5 897537-30130 Piston stopper Locking crankshaft rotation
6 897563-19830 Metering lever gauge Measuring metering lever height on carburettor
7 897603-23030 PTO shaft puller Removing PTO shaft
8 897701-02830 Bearing wedge Removing ball bearing remaining on crankshaft
9 897701-06030 Bearing wedge Removing ball bearing on PTO shaft / drive gear
10 897701-14732 Bearing tool Removing and installing ball bearings on crankcase / clutch drum
11 897702-30131 Piston pin tool Removing and installing piston pin (Use 10mm dia. adapter)
12 897712-04630 2-pin wrench Removing and installing pawl carrier
13 897714-12330 Oil seal tool Installing crankcase oil seal (clutch side)
14 897714-24330 Oil seal tool Installing crankcase oil seal (starter side) / PTO shaft bearings
15 897726-21430 Oil seal tool Installing crankcase oil seal (clutch side)
16 897718-03930 Bearing tool Installing crankcase oil seal (starter side)
17 897719-02830 Piston holder Making piston steady to remove and install piston / ring
18 363018-00310 Washer Installing crankcase oil seal (starter side)
19 897800-79931 Spark tester Checking ignition system
20 897803-30132 Pressure tester Testing fuel pipes/tank and crankcase leakages
21 897826-16131 Pressure plug Plugging intake port to test crankcase / cylinder sealing
22 897827-16131 Pressure plate Plugging intake port to test crankcase / cylinder sealing
23 897831-16131 Pressure plug Plugging exhaust port to test crankcase / cylinder sealing
24 91037 Compression gauge Measuring cylinder compression
25 Y089-000091 D-shaped tool Adjusting mixture needle
1-6 Special tools
1
78: a = 80 mm
9: a = 70 mm
19
3
10
20
22
12
54
11
17
2: b =6mm
21
6
16
23
14: a = 12 mm
b
= 32 mm
15: a = 15 mm
b
= 24.5mm
18
24
13
25

SERVICE INFORMATIONSRM-420ES 7
2 CARBURETTOR ADJUSTMENT PROCEDURE
2-1 General adjusting rules
A. Before starting the unit for adjustment, check the following items.
1. The correct spark plug must be clean and properly gapped.
2. The air filter element must be clean and properly installed.
3. The muffler exhaust port must be clear of carbon.
4. The fuel lines, tank vent and fuel filter are in good condition and clear of debris.
5.
The fuel is fresh ( > 89 octane : RON ) and properly mixed at 50 : 1 with “ISO L-EGD” or “JASO FC/FD” 2-stroke oil.
6. Install nylon line cutter with 2 nylon lines with 150 mm, even if 3-tooth blade is installed, for proper en-
gine loading to make sure engine speed on both SRM-420ES(L) and SRM-420ES(U).
B. Preliminary adjustment. Adjustment by Idle adjust screw of carburetor.
Start and run engine for 3 minute alternating engine speed between WOT for 50 seconds and idle for 10 sec-
onds.
Adjust idle engine speed to 2,800 +/- 100 r/min by turning Idle adjust screw. Confirm WOT engine speed
approx. 10,000 r/min. If engine does not run correctly after this adjustment, proceed to the next step 2-2.
2-2 Presetting Idle adjust screw, L mixture needle and H mixture needle
Tools Required : Small screwdriver with 2.5 mm
blade, P/N G310-000050 electronic tachometer,
P/N Y089-000091 D-shaped tool (A).
1. Turn L and H mixture needle clockwise until
lightly seated, and then turn out both mixture nee-
dles following turns.
L mixture needle (B) : 2 3/8
H mixture needle (C) : 3
NOTE : If needles are overtighented during seat-
ing, damage to carburettor may occur.
2. Remove air cleaner lid to expose the Idle adjust
screw and throttle plate. Turn Idle adjust screw (D)
anticlockwise until Idle adjust screw tip just touch-
es throttle plate. Then turn it clockwise 2 1/8 turns.
Reinstall air cleaner lid.
NOTE : The initial carburettor settings for Idle ad-
just screw, Idle and H mixture needles are intended
to start and run the engine before final carburettor
adjustments are made through this procedure. The
actual number of turns needed for engine opera-
tion may vary.
(A)
(D)
(C)
(B)

SERVICE INFORMATION SRM-420ES
8
2-3 Adjusting carburettor
SRM-420ES(L): Remove shield and cut trimmer
head line lengths to 190 mm.
SRM-420ES(U) : Remove shield and blade, and
cut trimmer head line lengths to 190 mm.
1. Start and warm engine for 3 minute alternating
engine speed between WOT for 50 seconds and
idle for 10 seconds.
2. Adjust L mixture needle (B) to reach maximum
idle speed using 2.5 mm blade screwdriver.
3. Set Idle speed to 3,550 r/min by turning Idle
adjust screw (D). Engine speed should be stable at
3,550 +/- 50 r/min.
4. Turn L mixture needle (B) anticlockwise to re-
duce engine idle speed 800 r/min to set idle speed
at 2,750 r/min. The idle speed range is 2,650 - 2,850
r/min.
5. Turn Idle adjust screw (D) clockwise to increase
idle engine speed to set idle at 2,800 r/min. The
idle speed range is 2,700 to 2,900 r/min.
NOTE : Engine speed must be allowed to stabilize
a minimum of 20 seconds after each adjustment of
idle mixture needle to assure accurate tachometer
readings.
6. Adjust H mixture needle (C) to reach maximum
WOT engine speed. Then turn H mixture needle (C)
anticlockwise to reduce WOT engine speed 120
r/min (RANG : 100-140 r/min).
max. approx. 9,000 r/min
NOTE : Nylon line length should be 190 mm with-
out shield.
7. SRM-420ES(L) : Stop engine, and restart en-
gine and verify engine idle speed ranges from 2,400
to 3,200 r/min, and expand and cut nylon line by
shield knife and WOT engine speed ranges from
9,500 to 10,500 r/min.
NOTE : Nylon line length should be 150 mm with
shield
SRM-420ES(U) : Stop engine and reinstall shield
for 3-tooth blade (255 mm) and the blade. Restart
engine and verify engine idle speed ranges from
2,400 to 3,200 r/min, and WOT engine speed
ranges from 10,500 to 11,500 r/min.
Make sure the nylon line cutter does not rotate
when engine is at idle. Engine should start and ac-
celerate smoothly.
NOTE : WOT, and idle speed in field operation
may vary from final adjustment specifications due
to changing ambient conditions, fuel, and engine
loads. Safe engine speed variances should be
within the WOT and Idle speed ranges listed in
Section 1-2, otherwise the carburettor should be
readjusted.
(C)
(B)
(D)
t = 190 mm