Page 1
SERVICE
MANUAL
Model
EH025/EH035
ENGINE
PUB-ES1740
Rev. 05/03
Page 2
940 Lively Blvd. • Wood Dale, IL 60191 • Phone: 630-350-8200 • Fax: 630-350-8212
e-mail: sales@robinamerica.com • www.robinamerica.com
© Copyright 2003 Robin America, Inc.
Page 3
CONTENTS
Section Title Page
1. SPECIFICATIONS....................................................................................................... 1
2. PERFORMANCE ........................................................................................................ 2
2-1 MAXIMUM OUTPUT........................................................................................................ 2
2-2 CONTINUOUS RATED OUTPUT .................................................................................... 2
2-3 MAXIMUM TORQUE AND FUEL CONSUMPTION WITH MAXIMUM OUTPUT............. 2
2-4 PERFORMANCE CURVES ............................................................................................. 3
3. FEATURES.................................................................................................................. 5
3-1 THE SMALLEST AND LIGHTEST 4-STROKE ENGINE IN THE MARKET..................... 5
4-STROKE ENGINE ALLOWING OPERATION IN THE TILTED POSITION,
3-2
REQUIRED IN BRUSH CUTTING WORK AND OTHER SIMILAR APPLICATIONS ......................
4. GENERAL DESCRIPTION OF ENGINE COMPONENTS .......................................... 8
4-1 CYLINDER BLOCK AND CRANKCASE.......................................................................... 8
4-2 CRANKSHAFT AND CONNECTING ROD ...................................................................... 8
4-3 PISTON............................................................................................................................ 8
4-4 PISTON RINGS ...............................................................................................................9
4-5 CAM GEAR...................................................................................................................... 9
4-6 COOLING SYSTEM......................................................................................................... 9
4-7 LUBRICATION SYSTEM ................................................................................................. 9
4-8 IGNITION SYSTEM ....................................................................................................... 10
4-9 CARBURETOR.............................................................................................................. 10
4-10 AIR CLEANER ............................................................................................................. 10
4-11 DECOMPRESSION SYSTEM.......................................................................................11
4-12 SECTIONAL VIEW OF ENGINE.................................................................................. 12
5
5. DISASSEMBLY AND REASSEMBLY ....................................................................... 14
5-1 PREPARATIONS AND SUGGESTIONS........................................................................ 14
5-2 SPECIAL TOOLS ........................................................................................................... 14
5-3 DISASSEMBLY PROCEDURES.................................................................................... 14
5-4 REASSEMBLY PROCEDURES..................................................................................... 26
6. MAGNETO ................................................................................................................ 41
6-1 FLYWHEEL MAGNETO................................................................................................. 41
6-2 IGNITION OF MAGNETO.............................................................................................. 41
7. AUTOMATIC DECOMPRESSION SYSTEM............................................................. 42
7-1 FUNCTION AND MECHANISM..................................................................................... 42
7-2 INSPECTION .................................................................................................................42
Page 4
Section Title Page
8. CARBURETOR ........................................................................................................ 43
8-1 OPERATION AND CONSTRUCTION............................................................................43
8-2 DISASSEMBLY AND REASSEMBLY.............................................................................44
9. RECOIL STARTER .................................................................................................. 47
9-1 HOW TO DISASSEMBLE..............................................................................................47
9-2 HOW TO REASSEMBLE...............................................................................................49
9-3 CHECK AFTER REASSEMBLE ....................................................................................50
9-4 OTHER GUIDES............................................................................................................50
10. TROUBLESHOOTING ........................................................................................... 51
10-1 STARTING DIFFICULTIES ..........................................................................................51
10-2 ENGINE MISFIRES .....................................................................................................52
10-3 ENGINE STOPS ..........................................................................................................52
10-4 ENGINE OVERHEATS ................................................................................................53
10-5 ENGINE KNOCKS .......................................................................................................53
10-6 ENGINE BACKFIRES THROUGH CARBURETOR.....................................................53
11. INSTALLATION ..................................................................................................... 54
11-1 INSTALLING.................................................................................................................54
11-2 VENTILATION..............................................................................................................54
11-3 EXHAUST GAS DISCHARGE .....................................................................................54
11-4 POWER TRANSMISSION TO DRIVEN MACHINES...................................................54
12. SERVICE DATA ...................................................................................................... 55
12-1 CLEARANCE DATA AND LIMITS ................................................................................55
12-2 TORQUE SPECIFICATIONS .......................................................................................58
12-3 OIL GRADE CHART ....................................................................................................59
13. MAINTENANCE AND STORAGE.......................................................................... 60
13-1 DAILY MAINTENANCE................................................................................................60
13-2 INITIAL 20 HRS. MAINTENANCE ...............................................................................60
13-3 EVERY 50 HRS. (10 DAYS) MAINTENANCE .............................................................60
13-4 EVERY 100-200 HRS. (MONTHLY) MAINTENANCE .................................................61
13-5 ENGINE STORAGE.....................................................................................................61
Page 5
1. SPECIFICATIONS
MODEL EH025 EH035
Type
Bore x Stroke 34 x 27 mm (1.34 x 1.06 in.) 39 x 28 mm (1.54 x 1.10 in.)
Piston Displacement 24.5 cm
Compression Ratio 8.3 8.6
Output
Max. Torque 1.18 N
Direction of Rotation Counterclockwise As Viewed From P.T.O. Shaft Side
Cooling system Forced Air Cooling
Valve Arrangement Overhead Valve
Lubrication Forced Lubrication
Lubricant Automotive Oil SAE #20, #30 or 10W-30 ; Class SF or higher
Capacity of Lubricant 0.08 liters (0.021 U.S. gal.) 0.10 liters (0.026 U.S. gal.)
Carburetor Diaphragm Type
Fuel Automotive Unleaded Gasoline
Continuous 0.55 kW (0.75 HP) /7000 r.p.m. 0.81 kW (1.10 HP) /7000 r.p.m.
Max. 0.81 kW (1.10 HP) /7000 r.p.m. 1.18 kW (1.60 HP) /7000 r.p.m.
・
m (0.12 kgf・m) /5000 r.p.m. 1.76 N・m (0.18 kgf・m) /5000 r.p.m.
Air-Cooled, 4-Cycle, Single-Cylinder,
Horizontal P.T.O. Shaft, Gasoline Engine
3
(1.49 cu.in.) 33.5 cm3(2.04 cu.in.)
Fuel Consumption Ratio
Fuel Feed System Diaphragm Pump
Fuel Tank Capacity 0.5 liters (0.13 U.S. gal.) 0.65 liters (0.17 U.S. gal.)
Ignition System Flywheel Magneto (Solid State)
Spark Plug NGK CMR6A (M10 x 1.0)
Starting System Recoil Starter
Air Cleaner Semi-Wet Type
Dry Weight 2.8 kg (6.17 lb.) 3.5 kg (7.72 lb.)
Dimensions (L x W x H)
408 g/kW
170 mm x 213 mm x 225 mm
(6.69 in. x 8.39 in. x 8.86 in.)
・
h (300 g/HP・h) 340 g/kW・h (250 g/HP・h)
At Continuous Rated Output
191 mm x 234 mm x 246 mm
(7.52 in. x 9.21 in. x 9.69 in.)
Specifications are subject to change without notice.
- 1 -
Page 6
2. PERFORMANCE
2-1 MAXIMUM OUTPUT
The maximum output is the output of an engine with its throttle valve fully opened under the condition that
all the moving parts are properly broken in after the initial break-in period. A new engine may not produce
full maximum output while its moving parts are still not broken-in.
2-2 CONTINUOUS RATED OUTPUT
The continuous rated output is the output of an engine at optimum governed speed which is most favorable from the view point of engine's life and fuel consumption. When the engine is installed on a certain
equipment, it is recommended that the continuous output required from the equipment should be kept
below this continuous rated output.
2-3 MAXIMUM TORQUE AND FUEL CONSUMPTION WITH MAXIMUM OUTPUT
The maximum torque is the torque at the output shaft when the engine is producing maximum output at
certain revolution. The fuel consumption rate is the amount of fuel in grams consumed per horsepowerhour when the engine is working at continuous rated output.
- 2 -
Page 7
2-4 PERFORMANCE CURVES
EH025
(PS)
(kW
1.2
1.0
0.8
0.6
OUTPUT
0.4
0.2
0
CLUTCH MEET
4000 - 4400 r.p.m.
1.0
0.8
0.6
0.4
0.2
0
(Nm)
MAXIMUM TORQUE
)
(kg-m
1.2
1.0
0.8
0.6
CONTINUOUS RATED
HORSEPOWER
MAXIMUM HORSEPOWER
RECOMMENDED
HORSEPOWER RANGE
600
) (
g/PSh
CLUTCH
CHARACTERISTICS
(g/kWh
)
0.12
0.10
0.08
TORQUEFUEL CONSUMPTION RATE
0.06
)
450
400
500
400
350
300
250
300
4000 5000 6000 7000
(r.p.m.)Revolution
8000
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Page 8
EH035
(PS)
(kW
1.6
1.4
1.2
1.0
OUTPUT
0.8
0.6
0.4
CLUTCH MEET
4000 - 4400 r.p.m.
1.2
1.0
0.8
0.6
0.4
0.2
(Nm)
MAXIMUM TORQUE
(kg-m
1.8
1.6
)
1.4
1.2
CONTINUOUS RATED
HORSEPOWER
MAXIMUM HORSEPOWER
RECOMMENDED
HORSEPOWER RANGE
(g/kWh
) (
g/PSh
600
)
0.18
0.16
0.14
TORQUEFUEL CONSUMPTION RATE
0.12
)
450
400
500
400
350
300
250
300
4000 5000 6000 7000
(r.p.m.)Revolution
8000
- 4 -
Page 9
3. FEATURES
3-1 THE SMALLEST AND LIGHTEST 4-STROKE ENGINE IN THE MARKET
1) Small-sized lubricant oil tank, thanks to the Robin original lubrication system.
2) Compact construction because of the optimum design, not taking any bore-up into consideration.
3) Shorter shaft length at the output side (magneto side), by arranging the cam gear unit at the opposite
side of the magneto.
4) Light weight construction, because of the resin made came gear, rocker cover and other parts.(EH025)
And because of the resin made came gear, other parts.(EH035)
5) Parts of the valve driving system with thoroughgoing light weight construction
3-2 4-STROKE ENGINE ALLOWING OPERATION IN THE TILTED POSITION, REQUIRED IN
BRUSH CUTTING WORK AND OTHER SIMILAR APPLICATIONS
1) Robin's original lubricating system
Small-sized lubrication system with high reliability , that makes it possible to operate the engine in tilted
position.
Basic system
Oil flow
Blow-by air (including fresh air) and oil mist
Fig. 3-1
- 5 -
Page 10
(a) Since Robin lubricating system makes use of the pressure fluctuations in the crankcase, a lead valve
is arranged at the lower part of the crankcase. By utilizing the negative pressure that occurs during
the piston rising stroke, lubricant oil is supplied from the oil tube (located inside the oil tank, that is
separated from the crankcase) to the crankcase, through the oil passage of the crankshaft which has
rotary valve that opens and shuts with an appropriate timing.
(b) At the same time, fresh air and blow-by air containing oil mist coming from the rocker arm compart-
ment are sucked through the two assist holes that open at the piston top dead center.
(c) The supplied oil is diffused by the crank arm and other parts, thereby transforming in mist.
That diffused oil mist is compressed during the piston lowering stroke, and an appropriate quantity of
the compressed oil mist is pumped to the cam gear compartment and to the rocker arm compartment
through the lead valve, and oil pasage. Thus, it lubricates the various parts of the engine. The remaining oil mist returns to the oil tank via bypass hole.
(d) The oil tank has two pressure relief holes located at its left and right sides which are connected to the
assist hole of the cylinder unit. These pressure relief holes have the function to keep the pressure of
the oil tank constant.
(e) Oil inside the rocker arm compartment is sucked back to the crankcase by the strong negative pres-
sure inside the crankcase, through the two return paths located at the left and right sides.
(f) The blow-by gas and a small amount of oil mist flow from the rocker arm compartment to the oil
separator inside the air cleaner, through the breather pipe. Then separated into blow-by gas and oil
mist.
(g) The separated oil mist returns into the crankcase, passing through the assist hole of the cylinder.
Engine operation in tilted positions
(a) When the engine is tilted carburetor side down.
The return path at the carburetor side inside
the rocker arm compartment comes to the
lower position. Then, the stagnant oil is sucked
back to the crankcase. At that time, the check
valve of the pressure relief hole prevents oil
from flowing back, because the carburetor side
pressure relief hole, located inside the oil tank,
is in the oil.
- 6 -
Fig. 3-2
Page 11
(b) When the engine is tilted muffler side down.
In the same way as that of the carburetor side
down, the return path in the rocker arm compartment and the pressure relief hole operate
and return the stagnant oil into the crankcase.
(c) Engine tilted back and forth
The breather hole located inside the rocker arm
compartment is arranged approximately at the
center of the rocker arm compartment, so as
to prevent stagnant lubricant oil from being
gushed out at either back or forth inclined position. The stagnant oil is sucked back into the
crankcase through the return path.
(d) Upside down position
Fig. 3-3
Basically, it is presumed that the engine is not
used (is not required to operate) continuously
in the upside down position, and only the practical tilted positions are taken into consideration
as priorities. Measures are adopted, however,
so that the engine can be run for a short time
in upside down positions during the work and/
or during idling.
The oil return passage tube at the muffler side
is extended up to the rocker arm cover in order to suck the oil that stagnates in the rocker
arm compartment while the engine is in the
upside down position. At that time, the pressure relief hole located inside the oil tank is
closed by the check ball, so as to prevent oil
from back flowing from the oil tank.
Fig. 3-4
Lubrication inside the cylinder is carried out with a sufficient volume of oil, irrespective of the position of
the engine, and there is no risk of engine seizure, wear and other similar problems caused by improper
lubrication. The oil volume supplied into the cam gear compartment and into the rocker arm compartment is limited to an appropriate amount, to minimize the oil consumption.
- 7 -
Page 12
4. GENERAL DESCRIPTION OF ENGINE COMPONENTS
4-1 CYLINDER BLOCK AND CRANKCASE
The cylinder block and crankcase are aluminum
die-castings split in upper and lower parts.
The cylinder block and the cylinder head are a
single piece. The valve seats are molded and the
valve guides (intake valves and exhaust valves)
and the valve stem seal (intake side only) are
press fitted. The cylinder bore is finished with hard
chromium plating.
Fig. 4-1
4-2 CRANKSHAFT AND CONNECTING ROD
The crankshaft is made of malleable cast iron, and
the entire crank pin surface is hardened by cementation.
The crank gear is press fitted at the opposite side
to the P.T.O..
CONNECTING ROD
CRANKSHAFT
The connecting rod is a carbon steel casting, and
needle roller bearings are press fitted in the large
and small ends.
4-3 PISTON
The piston is made of high silicon alminun, and
measures are taken to improve its wearing resistance.
Fig. 4-2
PISTON
- 8 -
Fig. 4-3
Page 13
4-4 PISTON RINGS
The piston rings are made of special cast iron. The top ring is a barrel face type, the second ring is a
tapered one, and the oil ring consists of three pieces, so as to reduce the oil consumption.
4-5 CAM GEAR
The cam gear consists of the combination of the
cam and the gear. The cam is a sintered component, widely used in this kind of application. The
gear is made of synthetic resin to reduce both
weight and gear noise.
1
2
3
Fig. 4-4
1
2
3
TOP
RING
SECOND
RING
OIL RING
BARREL
TAPER
THREE-PIECE
ASSEMBLY
4-6 COOLING SYSTEM
Fig. 4-5
This engine adopts the forced air-cooled system, where cooling air is sent to the cylinder block by an
even-pitched cooling fan that works as a flywheel as well. This cooling air is guided properly to the
cylinder block by the baffle plate.
4-7 LUBRICATION SYSTEM
The rotary parts and the sliding parts of the engine are lubricated by lubricant oil, which is forcibly supplied by utilizing the pressure generated by the up-down movement of the piston. Moreover, the oil
compartment is provided separately in order to prevent lubricant oil from flowing directly into the cylinder.
- 9 -
Page 14
4-8 IGNITION SYSTEM
The ignition system is a TIC flywheel magneto
type. The ignition timing is 25 degrees before the
top dead center.
The magneto consists of the flywheel and the ignition coil. The flywheel (that works as a cooling
fan as well) is mounted on the crankshaft and the
ignition coil is mounted directly on the cylinder
block.
4-9 CARBURETOR
This engine adopts a diaphragm type carburetor.
The carburetor is calibrated carefully for easy starting, good acceleration, low fuel consumption and
sufficient output.
Fig. 4-6
4-10 AIR CLEANER
The air cleaner element is urethane foam (semiwet type).
This air cleaner has a compartment that separates
blow-by gas from lubricant oil.
EH025
EH035
Fig. 4-7
ELEMENT
PLATE
AIR CLEANER COVER
FIXING BOLT
ELEMENT
PLATE
AIR CLEANER COVER
FIXING BOLT
Fig. 4-8
-
10
-
Page 15
4-11 DECOMPRESSION SYSTEM
The decompression equipment is installed inside
the gear of the cam-gear unit. The decompression equipment opens the intake valve before the
compression top to relieve the compression pressure for easy start.
CAMLIFTER
WEIGHT
CRESCENT CAM
Fig. 4-9
-
11
-
Page 16
4-12 SECTIONAL VIEW OF ENGINE
CARBURETOR
AIR
CLEANER
RETURN
PIPE
BREATHER PIPE
INTAKE VALVE
EXHAUST VALVE
MUFFLER COVER
MUFFLER
CONNECTING
ROD
CHECK BALL
Fig. 4-10
OIL GAUGE
-
12
-
Page 17
SPARK PLUG
ROCKER ARM
PUSH ROD
PISTON
IGNITION COIL
FLYWHEEL
PISTON RING
PISTON PIN
CAM GEAR
RECOIL
STARTER
FUEL TANK
Fig. 4-11
-
13
-
OIL TUBE
Page 18
5. DISASSEMBLY AND REASSEMBLY
5-1 PREPARATIONS AND SUGGESTIONS
1) When disassembling the engine, memorize the locations of individual parts so that they can be
reassembled correctly. If you are uncertain of identifying some parts, it is suggested attach tags to
them.
2) Have boxes ready to keep disassembled parts by group.
3) To prevent losing and misplacing, temporarily assemble each group of disassembled parts.
4) Carefully handle disassembled parts, and clean them with washing oil if necessary.
5) Use the correct tools in the correct way.
5-2 SPECIAL TOOLS (EH025 ONLY)
Tool No. Tool Use
560-90020-00 Flywheel puller For pulling off the flywheel
Fig. 5-1
5-3 DISASSEMBLY PROCEDURES
Step Parts to remove Remarks and procedures Fasteners
Engine oil drain Remove the oil gauge.
Plug cover, plug cap, stop switch 1)
1
Engine cover Remove engine cover from blower
Remove plug cover from engine
cover.
Remove the plug cap.
2)
Disconnect lead wire of stop
3)
switch from ignition coil
(Except Stop switch : EH035)
*Hold lead wire with plier and pull
it out straight.
housing and recoil.
M5x8 mm: 1 pce.
(EH035)
M5x12 mm: 2 pcs.
(EH025)
M4x16 mm: 2 pcs.
(EH025)
M5x12 mm: 3 pcs.
(EH035)
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14
-
Page 19
OIL GAUGE
EH025
PLUG COVER
Fig. 5-2
Fig. 5-3
Fig. 5-4
M5 x 8 SCREW : 1 pce.
STOP SWITCH
EH035
PLUG COVER
STEP 1 STEP 1
ENGINE COVER
ENGINE COVER
LEAD WIRE
M5 x 12 SCREW AND
WASHER AY : 1 pce.
M5 SCREW AND
WASHER : 2 pcs.
Fig. 5-5
M4 SCREW AND
WASHER : 2 pcs.
M5 x 12 SCREW AND
WASHER AY : 2 pcs.
-
15
-
Fig. 5-6
Page 20
Step Parts to remove Remarks and procedures Fasteners
Air cleaner, insulator, insulator
carburetor
2
*Breather unit of the air cleaner (plate
separator, check valve)
*Disassemble the breather unit
only if necessary.
1)
Remove air cleaner cover and air
cleaner element.
2)
Remove fuel tube from carburetor,
and then remove breather pipe and
return pipe from cylinder.
It is convenient to use a small-sized
screwdriver to remove tubes.
3)
Remove air cleaner plate.
The air cleaner plate is fastened
together with the carburetor.
4)
Remove insulator and insulator
carburetor.
1)
Remove the plate separator.
Make sure of removing the plate
separator by holding its edge.
When holds the square pipe, there is
risk of damaging the pipe.
2)
Remove the check valve plate
(fastened together with the check
valve) with a small-sized screwdriver.
It is recommendable to pry the hook
of the check valve plate with a screwdriver to remove the plate.
3)
Remove the check valve (1).
M5 x 14 mm ; 1 pc.
M5 x 68 mm; 2 pcs.
M5 x 18 mm ; 2pcs.
M5 x 12 mm ; 1pce.
-
16
-
Page 21
EH025
CHOKE PLATE
PLATE
M5 x 40
SCREW : 2 pcs.
CHOKE LEVER
AIR CLEANER
PLATE
O-RING
CARBURETOR
AIR CLEANER
COVER
M5 x 14 SCREW
AND WASHER
: 1 pce.
PLATE,
SEPARATOR
STEP 2
INSULATOR,
CARBURETOR
GASKET,
CARBURETOR
ELEMENT
CHECK
VALVE
CHECK VALVE
PLATE
GASKET,
SEPARATOR
INSULATOR
M5 x 12 SCREW
AND WASHER : 1 pce.
BREATHER PIPE
CHECK
VALVE (1
O-RING
GASKET,
INSULATOR
M5 x 18
SCREW AND
WASHER : 2 pcs.
SPACER
RETURN
PIPE
)
RETURN PIPE
Fig. 5-8
Fig. 5-9
EH035
CHOKE PLATE
PLATE
M5 x 40
SCREW : 2 pcs.
AIR CLEANER
COVER
M5 x 14 SCREW
AND WASHER
: 1 pce.
PLATE,
SEPARATOR
Fig. 5-7
STEP 2
CHOKE LEVER
CARBURETOR
ELEMENT
O-RING
CHECK VALVE PLATE
CHECK VALVE
GASKET, SEPARETOR
INSULATOR,
CARBURETOR
GASKET,
CARBURETOR
O-RING
AIR CLEANER
PLATE
RETURN PIPE
CHECK VALVE (1
GASKET,
INSULATOR
INSULATOR
M5 x 18 SCREW AND WASHER : 2 pcs.
M5 x 12 SCREW AND WASHER : 1 pce.
)
Fig. 5-10
Fig. 5-11
-
17
-
Page 22
Step Parts to remove Remarks and procedures Fasteners
Muffler and Muffler cover Remove the muffler cover from the
muffler.
The muffler and the muffler cover are
fastened together with two M5 x 40 mm
socket head bolts.
Recoil starter Remove recoil starter from crankcase.
3
Fuel tank Remove fuel tank from housing blower.
Pulley Remove the pulley from the crank-
shaft. Utilize the hole of the pulley, and
remove the pulley by tapping it with a
metallic rod and a hammer. (The thread
is clockwise).
M5 x 5mm; 1 pc.
M5 x 40mm
socket head bolt ;
2 pcs.
M4 x16mm; 2 pcs.
(EH025)
M5 x14mm; 4 pcs.
(EH035)
M5 SOKET HEAD
BOLT : 2 pcs.
HOLE OF THE PULLEY
Fig. 5-12
FUEL
TANK
EH025
Fig. 5-13
STEP 3
PULLEY
M4 SCREW AND
WASHER : 2 pcs.
MUFFLER
GASKET
RECOIL
STARTER
M5 SCREW : 1 pc.
MUFFLER
COVER
MUFFLER
EH035
RECOIL
STARTER
PULLEY
M5 SCREW AND
WASHER : 4 pcs.
-
18
-
Page 23
Step Parts to remove Remarks and procedures Fasteners
Blower housing Remove blower housing from cylinder
and crankcase
4
Clutch Remove the clutch from the flywheel.
EH025
M5 SCREW AND
WASHER : 3 pcs.
BLOWER HOUSING
M6 BOLT,
CLUTCH : 2 pcs.
STEP 4
SPRING
M5 x18mm; 3 pcs.
(EH025)
M5 x16mm; 4 pcs.
(EH035)
M6 x23mm; 2 pcs.
(EH025)
M8 x23.5mm; 2 pcs.
(EH035)
EH035
M5 SOCKET
HEAD BOLT : 4 pcs.
BLOWER HOUSING
CLUTCH
M8 BOLT,
CLUTCH : 2 pcs.
STEP 4
SPRING
CLUTCH
Fig. 5-14
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19
-
Page 24
Step Parts to remove Remarks and procedures Fasteners
Flywheel 1) Remove flywheel from crankshaft.
*Use the flywheel puller as shown
in the Figure, and remove the flywheel by rotating the center shaft
5
Ignition coil
clockwise.
Remove ignition coil from cylinder
block.
M4 x 20 mm ;
2 pcs.
Spark plug
Remove the spark plug from the cylinder block
SPARK PLUG
STEP 5
IGNITION COIL
Fig. 5-15
M4 SCREW AND
WASHER : 2 pcs.
FLYWHEEL
Fig. 5-16
-
20
-
M6 BOLT AND
WASHER : 1 pce.
Page 25
Step Parts to remove Remarks and procedures Fasteners
Oil case 1)2)Remove oil case from crankcase.
Remove the oil case from the
recoil side of the crankcase, by
tapping the oil case with a plastic
or wooden hammer.
Oil tube and Retainer plate 1)2)Pull out the oil tube, by holding its
6
base. It is recommendable to pry
the oil tube with a small-sized
screwdriver.
Remove retainer plate from crank-
case. When removing the retainer
plate, take care not to lose the
lead valve.
M5 x18 mm;
4 pcs.
M4 x10 mm; 1 pc.
OIL TUBE
LEAD VALVE
RETAINER PLATE
M4 SOCKET HEAD
BOLT : 1 pce.
Fig. 5-18
STEP 6
GASKET, CASE
OIL CASE
M5 SCREW AND
WASHER : 4 pcs.
Fig. 5-17
OIL TUBE
OIL WEIGHT
-
21
-
Page 26
Step Parts to remove Remarks and procedures Fasteners
Rocker cover Remove rocker cover from cylinder
block.
Cam gear cover Remove cam gear cover from cylinder
block.
Cam lifter, Cam gear and
Push rod
7
1)
Position the cam peak portion
down, then remove the cam lifter
shaft, and remove the cam lifter.
2)
Remove the cam gear shaft, and
remove the cam gear.
3)
Remove the push rod.
Rocker arm Remove the rocker arm shaft, then re-
move the rocker arm. Hold the rocker
arm shaft, that can be seen between
the intake and exhaust rocker arm,
with pincers, then remove the shaft.
M5 SCREW AND
WASHER : 3 pcs.
M5 x 16mm ; 3 pcs.
(EH025)
M5 x 16mm ; 4 pcs.
(EH035)
M5 x 14mm ; 3 pcs.
ROCKER ARM
ADJUSTING SCREW
STEP 7
GASKET,
ROCKER COVER
ROCKER SHAFT
ROCKER COVER
PUSH ROD
GASKET,
CAMGEAR COVER
CAMGEAR COVER
CAMLIFTER
SHAFT
M5 SCREW AND
WASHER : 3 pcs.
CAMLIFTER
CAMGEAR
Fig. 5-19
CAMGEAR SHAFT
Fig. 5-20
-
22
-
Page 27
Step Parts to remove Remarks and procedures Fasteners
Crankcase Remove the crankcase from the
cylinder block by tapping it with a
plastic or wooden hammer from the
recoil side. Take care not to lose the
check balls (2 pcs.) that are held by
8
the washer of the screw.
Crankshaft Remove crankshaft from cylinder
block. When removing the crankshaft
from the cylinder block, take care not
to damage the oil seal.
M5 x 14mm ; 8 pcs.
(EH025)
M5 x 16mm ; 4 pcs.
(EH035)
M5 x 33mm ; 4 pcs.
(EH035)
M5 SOCKET HEAD
BOLT : 8 pcs.
Fig. 5-21
CYLINDER BLOCK
STEP 8
CRANKSHAFT
CRANKCASE
Fig. 5-22
-
23
-
Page 28
Step Parts to remove Remarks and procedures Fasteners
Valve, Valve spring and
9
Spring retainer
Hold the valve from the inner side of the
cylinder, then push the spring retainer
and remove it by sliding.
SPRING RETAINER
VALVE SPRING
STEP 9
INTAKE VALVE
EXHAUST VALVE
Fig. 5-23
SPACER
Fig. 5-24
-
24
-
Page 29
Step Parts to remove Remarks and procedures Fasteners
Piston and Piston ring 1)2)Remove the two piston clips, take
out the piston pin, and then
remove the piston from the small
end of the connecting rod.
When removing the piston, take
care to prevent dust from getting in
the bearing at the connecting rod
10
small end.
To remove the two piston rings
and the oil ring, open wide the
open end of the rings and remove
them from the piston.
Take care not to widen the open
end of the rings too much, or the
rings may break.
CLIP
PISTON
STEP 10
PISTON RING
PISTON PIN
CLIP
CRANKSHAFT
Fig. 5-25
-
25
-
Page 30
5-4 REASSEMBLY PROCEDURES
● PRECAUTIONS FOR REASSEMBLY
1) Clean parts thoroughly before reassembly.
Pay most attention to cleanliness of piston, cylinder, crankshaft, connecting rod and bearings.
2) Scrape off all carbon deposits from cylinder head, piston top and piston ring grooves.
3) Check lip of oil seals. Replace oil seal if the lip is damaged. Apply oil to the lip before reassembly.
4) Replace all the gaskets with new ones.
5) Replace keys, pins, bolts, nuts, etc., if necessary.
6) Torque bolts and nuts to specification referring to the "TORQUE SPECIFICATIONS".
7) Apply oil to rotating and sliding portions.
8) Check and adjust clearances and end plays where specified in this manual.
9) Check resistance and/or noise by rotating parts by hand, when reassemble main parts.
5-4-1 CYLINDER BLOCK, VALVE SPRING AND SPRING RETAINER
(1) Before reassemble, apply 4 cycle engine oil
(10W-30) to cylinder inner surface, piston slide
face and valve guide holes.
SPRING RETAINER
(2) Install valve spring and spring retainer as
shown in Fig. 5-26. Push spring retainer down
until valve stem comes through the hole of
spring retainer, then slide the spring retainer.
1.INSERT THE
VALVE SPRING
2.SLIDE THE
SPRING RETAINER
SPRING
RETAINER
VALVE
SPRING
Fig. 5-26
VALVE SPRING
SPACER MOUNTING
POSITION
INTAKE VALVE
SPACER
EXHAUST VALVE
Fig. 5-27
-
26
-
Page 31
5-4-2 CONNECTING ROD, PISTON AND PISTON RINGS
Install the piston on the connecting rod
(1) After installing the piston rings, apply 4-cycle engine oil to the rings.
NOTE ;
Install the top ring and the second ring with their open ends displaced by 180 degrees. When installing a
new ring, place the white mark at the right-hand side, and when reassembling a used one, install it with
the contact face down.
WHITE MARK
CLIP
PISTON
1
2
3
PISTON RING
PISTON PIN
CLIP
Fig. 5-28
1
2
3
TOP
RING
SECOND
RING
OIL RING
BARREL
TAPER
THREE-PIECE
ASSEMBLY
CRANKSHAFT
APPLY GREASE
ON THE INNER FACE
Fig. 5-29
-
27
-
Page 32
5-4-3 CYLINDER BLOCK AND CRANKCASE
Installing cylinder block and crankcase
Make sure that the liquid packing (Three Bond 1216) is evenly applied on the crankcase before installing
the cylinder block.
Tightening torque of the hexagonal socket head bolts (8 pce.) of the lower part of the crankcase :
Tightening torque : 4.5 - 6.5 N・m
(45 - 65 kgf・cm)
(3.3 - 4.7 ft・lb.)
M5 SOCKET HEAD
BOLT : 8 pcs.
CYLINDER
BLOCK
CRANKCASE
LOWER PART
Tightening order
6
1
Fig. 5-30
4
7
Fig. 5-31
2
LIQUID PACKING
(THREE BOND 1216)
8
3
5
M5 SOCKET HEAD
BOLT : 8 pcs.
DO NOT APPLY LIQUID
PACKING IN EXCESS
CRANKCASE
M5 x 16 SOCKET
HEAD BOLT : 4 pcs.
Fig. 5-32
M5 x 33 SOCKET
HEAD BOLT : 4 pcs.
-
28
Fig. 5-33
-
Page 33
5-4-4 OIL CASE
Install the lead valve with the cutout facing to the
oil filling port.
Retainer plate M4 x 10 mm hexagonal socket head
bolt (1 pc.)
Oil case M5 x 18 mm screw, and washer (4 pcs.)
Tightening torque
M4 BOLT M5 SCREW
3 - 4 N・m
(30 - 40 kgf・cm)
(2.2 - 2.9 ft・lb.)
4 - 5.5 N・m
(40 - 55 kgf・cm)
(2.9 - 4.0 ft・lb.)
M4 SOCKET HEAD
BOLT : 1 pce.
RETAINER PLATE
LEAD VALVE
CUTOUT
OIL CASE
GASKET, CASE
M5 SCREW AND
WASHER : 4 pcs.
OIL WEIGHT
OIL TUBE
*ASSEMBLE
SEPARATELY
CRANKCASE
LOWER PART
Fig. 5-34
-
29
-
Page 34
5-4-5 FLYWHEEL
Installing the flywheel
Degrease the crankshaft and the tapered portion
of the flywheel perfectly when installing them.
Align the flywheel key with the crankshaft key
groove.
Flywheel tightening bolt M6 x 16 mm, with spring
washer :
Tightening torque : 9 - 12 N・m
(90 - 120 kgf・cm)
(6.5 - 8.8 ft・lb.)
Fig. 5-35
FLYWHEEL
5-4-6 IGNITION COIL
Installing the ignition coil (Air gap adjustment)
Air gap :0.3 mm
Ignition coil tightening torque
M4 x 20 mm, with washer and spring washer
(2 pcs.)
NOTE :
Measure the air gap between the flywheel magnet and the ignition coil.
Tightening torque : 2 - 4 N・m
(20 - 40 kgf・cm)
(1.4 - 2.9 ft・lb.)
M6 BOLT AND
WASHER : 1 pc.
Fig. 5-36
PLUG CAP
THICKNESS GAUGE
IGNITION
COIL
FLYWHEEL
Fig. 5-37
-
30
-
Page 35
5-4-7 BLOWER HOUSING
Installing the blower housing.
Blower housing tightening torque
M5 x 18 mm Screw : 3 pcs. (EH025)
M5 x 16 mm Socket hesd bolt : 4 pcs. (EH035)
Tightening torque : 4 - 5.5 N・m
(40 - 55 kgf・cm)
(2.9 - 4.0 ft・lb.)
5-4-8 CAM GEAR
Installing the cam gear.
(1) Align the mark punched on the flywheel (key
position groove) with the timing mark on the
ignition coil.
M5 SCREW AND
WASHER : 3 pcs.
BLOWER HOUSING
Fig. 5-38
TIMING MARK
(2) Install the cam gear with the cam top facing
down vertically (use the timing mark for
reference).
TIMING MARK
Fig. 5-40
Fig. 5-39
CAMGEAR
SHAFT,
CAMGEAR
Fig. 5-41
-
31
-
Page 36
5-4-9 PUSH ROD, CAMLIFTER AND ROCKER ARM
Installing the push rod, cam lifter and rocker arm
(1) Apply sufficient oil in the rocker shaft hole.
(2) Install the cam lifter.
(3) Pass the push rod through the hole of the cyl-
inder block. Align the push rod end with the
cam lifter ball groove.
APPLY A SUFFICIENT AMOUNT OF OIL
Fig. 5-42
ADJUSTING SCREW
BALL
GROOVE
PUSH ROD
BALL
GROOVE
(4) Install the rocker arm assembly. Align the push
rod end with the ball groove of the adjusting
screw.
-
32
CAM LIFTER
Fig. 5-43
ROCKER
ARM
ADJUSTING
SCREW
PUSH ROD
CAM LIFTER SHAFT
CAM LIFTER
Fig. 5-44
-
Page 37
5-4-10 CAMGEAR COVER
Installing the cam gear cover
Before installing the cam gear cover, apply oil on
the camgear and the cam lifter sliding surface.
Camgear cover tightening torque M5 x 14 mm
screw (3 pcs.)
Tightening torque : 4 - 5.5 N・m
(40 - 55 kgf・cm)
(2.9 - 4.0 ft・lb.)
CAMGEAR COVER
Fig. 5-45
GASKET,
CAMGEAR COVER
CAMGEAR COVER
5-4-11 VALVE CLEARANCE ADJUSTMENT
Loosen the nut and adjust the valve clearance by
rotating the adjusting screw with a hexagon bar
wrench. Adjust the valve clearance at the compression top dead center.
After the adjustment, tighten the nut firmly.
Valve clearance : 0.15 mm
(0.0059 in.)
Tightening torque : 5 - 6.5 N・m
(50 - 65 kgf・cm)
(3.6 - 4.7 ft・lb.)
M5 SCREW AND
WASHER : 3 pcs.
Fig. 5-46
THICKNESS GAUGE
ADJUSTING SCREW
Fig. 5-47
-
33
-
Page 38
5-4-12 ROCKER COVER
Before installing the rocker cover, apply oil on the
sliding surfaces of the rocker arm and the valve
stems.
Rocker cover tightening torque
ROCKER COVER
M5 SCREW AND
WASHER : 3 pcs.
M5 x 16 mm screw : 3 pcs. (EH025)
M5 x 16 mm screw : 4 pcs. (EH035)
GASKET,
ROCKER COVER
Tightening torque : 4 - 5.5 N・m
(40 - 55 kgf・cm)
(2.9 - 4.0 ft・lb.)
5-4-13 PULLEY, FUEL TANK AND RECOIL STARTER
Install the pulley on the crankshaft.
Pulley tightening torque :
Tightening torque : 4 - 5.5 N・m
(40 - 55 kgf・cm)
(2.9 - 4.0 ft・lb.)
Install the tank on the main bearing cover.
Install the recoil on the crankcase.
Recoil tightening torque
M4 x 16 mm screw : 2 pcs. (lower side) (EH025)
Tightening torque : 1 - 2.5 N・m
(10 - 25 kgf・cm)
(0.7 - 1.8 ft・lb.)
M5 x 14 mm screw : 4 pcs. (EH035)
PLATE
PLATE
Fig. 5-48
M5 SOCKET HEAD BOLT : 2 pcs.
MUFFLER COVER
M5 SCREW
: 1 pce.
MUFFLER
GASKET, MUFFLER
A
FUEL TANK
Tightening torque : 1 - 2.5 N・m
(10 - 25 kgf・cm)
(0.7 - 1.8 ft・lb.)
5-4-14 MUFFLER AND MUFFLER GASKET
Install the gasket, muffler and muffler cover on
the cylinder head exhaust port.
M5 x 40 mm socket head bolt (2 pcs.)
M5 x 5 mm screw (1 pc.)
Tightening torque
M5 BOLT M5 SCREW
7 - 9 N・m
(70 - 90 kgf・cm)
(5.1 - 6.5 ft・lb.)
3 - 5 N・m
(30 - 50 kgf・cm)
(2.2 - 3.6 ft・lb.)
DAMPER
EH025
PULLEY
RECOIL
STARTER
A
M4 SCREW AND
WASHER : 2 pcs.
Fig. 5-49
-
34
-
EH035
A
PULLEY
M5 SCREW AND
WASHER : 4 pcs.
RECOIL
STARTER
Page 39
5-4-15 INSULATOR AND INSULATOR CARBURETOR
Cover the insulator on the insulator carburetor and
tighten them together.
M5 x 18 mm screw : 2 pcs. (EH025, EH035)
M5 x 12 mm screw : 1 pc. (EH025, EH035)
Tightening torque : 4 - 5.5 N・m
(40 - 55 kgf・cm)
(2.9 - 4.0 ft・lb.)
NOTE :
The end face of the adjustment screw shall be
aligned with the insulator end face (no protrusion).
The angular side of the gasket shall face up.
EH025
INSULATOR,
CARBURETOR
M5 x12
SCREW AND
WASHER : 1 pc.
EH035
INSULATOR,
CARBURETOR
INSULATOR
GASKET,
INSULATOR
INSULATOR
M5 x 18 SCREW AND
WASHER : 2 pcs.
GASKET,
INSULATOR
M5 x12 SCREW AND
WASHER : 1 pc.
Approx. 2 mm
M5 x 18 SCREW AND
WASHER : 2 pcs.
Fig. 5-50
Alignment
Fig. 5-51
-
35
-
Page 40
5-4-16 CARBURETOR AND AIR CLEANER
(a) Assemble the plate, choke plate, air cleaner plate, carburetor, gasket carburetor, spacer, o-ring,
breather pipe and return pipe.
NOTE :
When installing the choke plate, keep the choke lever fully closed. (lever touching the upper stopper).
Apply grease or silicone on the choke plate after installing it.
Air cleaner tightening torque Air cleaner tightening torque
M5 x 68 mm screw : 2 pcs. M5 x 14 mm screw : 1 pce.
Tightening torque : 2 - 4 N・m
(20 - 40 kgf・cm)
(1.4 - 2.9 ft・lb.)
EH025
CHOKE LEVER
CHOKE PLATE
PLATE
M5 SCREW
: 2 pcs.
AIR CLEANER
COVER
M5 SCREW
AND WASHER
: 1 pce.
PLATE,
SEPARATOR
ELEMENT
CHECK VALVE
GASKET, SEPARATOR
AIR CLEANER
PLATE
CHECK
VALVE (1
O-RING
CHECK VALVE
PLATE
GASKET,
CARBURETOR
CARBURETOR
O-RING
SPACER
BREATHER PIPE
RETURN
PIPE
)
Tightening torque : 0.5 - 1 N・m
(5 - 10 kgf・cm)
(0.35 - 0.7 ft・lb.)
EH035
CHOKE PLATE
PLATE
M5 SCREW
: 2 pcs.
AIR CLEANER
COVER
M5 SCREW AND
WASHER : 1 pce.
PLATE,
SEPARATOR
CHOKE LEVER
CARBURETOR
O-RING
ELEMENT
CHECK VALVE (1
O-RING
CHECK VALVE
PLATE
CHECK VALVE
GASKET, SEPARATOR
GASKET,
CARBURETOR
AIR CLEANER
PLATE
BREATHER PIPE
RETURN PIPE
)
Fig. 5-52
STOPPER (UPPER)
-
36
-
STOPPER
(LOWER)
STOPPER (UPPER)
STOPPER
(LOWER)
CHOKE OPENCHOKE CLOSE
Fig5-53
Page 41
(b) Connect the fuel tank tube to the fuel joint of
the carburetor. (Check the bent of the tube).
(c) Connect the return pipe to the pipe joint at the
center of the cylinder.
BREATHER PIPE
HOSE CLAMP
AIR CLEANER PLATE
UPPER CLAW
(d) Connect the breather pipe to the pipe on the
rocker cover and fasten it with the hose clamp.
(e) Install the air cleaner cover after hooking it on
the upper claw of the air cleaner plate.
5-4-17 SPARK PLUG
Installing the spark plug.
Tightening torque : 9 - 13 N・m
(90 - 130 kgf・cm)
(6.5 - 9.4 ft・lb.)
RETURN
PIPE
TUBE
TUBE
Fig. 5-54
5-4-18 CLUTCH
Install the clutch with the “← ”(EH025),
“R”(EH035) mark on the clutch shoe at the front
side (facing the assembly worker).
Bolt (clutch)
M6 x 23mm : 2 pcs. (EH025)
M8 x 23.5mm : 2 pcs. (EH035)
Tightening torque : 7.5 - 10 N・m
(75 - 100 kgf・cm)
(5.4 - 7.2 ft・lb.)
M6 BOLT : 2 pcs. (EH025)
M8 BOLT : 2 pcs. (EH035)
SPRING
CLUTCH
Fig. 5-55
-
37
-
Page 42
5-4-19 ENGINE COVER, STOP SWITCH AND PLUG COVER
Installing the engine cover, stop switch and plug
cover.
(1) Assemble the stop switch on the engine cover
in advance. Connect the stop switch wire to
the terminal of the switch. (EH025)
(2) Faston terminals (2 places) from the stop
switch. (EH025)
Either Faston terminal can be connected with
the coil terminal. (EH025)
Faston terminals (2 places) of the coil. (EH025)
The cylinder side is the grounding terminal.
(EH025)
※ Install the engine cover by placing it on the
engine from above, and screw its front side
on the blower housing (two places) and its rear
side on the crankcase (two places). (screw the
rear side together with the recoil).
MUFFLER
NOTE :
When installing the engine cover, make sure that
there is no coil terminal disconnected and no high
voltage cord bent.
ENGINE COVER
Fig. 5-56
THE INSULATOR CARBURETOR
SHALL BE PLACED INSIDE.
Fig. 5-57
-
38
-
Page 43
(4) Install the plug cover by hooking the lower claw on
the engine cover first and then fitting its upper part.
M5 x 12 mm screw (2 pcs.) (EH025,EH035)
Tightening torque : 2 - 4 N・m
(20 - 40 kgf・cm)
(1.4 - 2.9 ft・lb.)
M5 x 8 mm screw (1 pce.) (EH035)
Tightening torque : 1.5 - 3 N・m
(15 - 30 kgf・cm)
(1.1 - 2.1 ft・lb.)
M4 x 16 mm screw (2 pcs.) (EH025) M5 x 14 mm screw (1 pce.) (EH035)
Tightening torque : 1 - 2 N・m
(10 - 20 kgf・cm)
(0.7 - 1.4 ft・lb.)
EH025
PLUG COVER
STOP SWITCH
ENGINE COVER
EH035
PLUG COVER
ENGINE COVER
Tightening torque : 1 - 2 N・m
(10 - 20 kgf・cm)
(0.7 - 1.4 ft・lb.)
M5 x 8 SCREW : 1 pce.
M5 x 14 SCREW
AND WASHER
M5 x 12 SCREW AND
WASHER : 2 pcs.
M4 x 16 SCREW AND
WASHER : 2 pcs.
Fig. 5-58
-
M5 x 12 SCREW AND
WASHER AY : 2 pcs.
39
-
Page 44
5-4-20 ENGINE OIL, OIL GAUGE
(1) Place the engine horizontally and fill oil from
the oil filling port up to the threaded mouth.
Use Robin genuine oil or engine oil class SF
or higher.
Oil capacity : EH025 0.08L (80 cc)
EH035 0.10L (100 cc)
(2) After filling oil, tighten the oil gauge.
(3) Test run
An engine that has been completely overhauled should be thoroughly RUN-IN, especially when the cylinder, piston rings, valves,
etc., have been changed with new ones.
-
End of the reassembly
-
OIL GAUGE
Fig. 5-59
Fig. 5-60
UPPER LIMIT
(
MOUTH OF THE OIL
CHARGING PORT
OIL LEVEL
)
-
40
-
Page 45
6. MAGNETO
6-1 FLYWHEEL MAGNETO
The ignition system of the EH025 is the T.I.C. (Transistor, Igniter, Circuit) point less ignition system.
6-2 IGNITION OF MAGNETO
When the engine does not start, has difficulty in starting or does not run correctly, carry out the following
checks for magneto failure.
(1) Check carefully the high voltage wiring for damage and short-circuit.
(2) Check the spark.
1) Remove the spark plug from the cylinder and connect the spark plug with the plug cap and ground
it to the cylinder. (The electrode gap of the spark plug should be 0.7 to 0.8 mm.)
2) Rotate the flywheel by pulling the recoil starter and check the spark and examine the intensity of
the spark.
3) If the plug does not spark, remove the spark plug and the plug cap, place the high voltage wire end
a few millimeters away from the cylinder, pull the recoil starter and check whether the high voltage
wire end sparks.
-
41
-
Page 46
7. AUTOMATIC DECOMPRESSION SYSTEM
7-1 FUNCTIONS AND MECHANISM
The decompression system is installed on the cam in order to open the intake valve and relieve the
compression pressure at the first half of the engine compression cycle. The flyweight installed inside the
cam gear has an appropriate shape (weight) to have the effect of the centrifugal force, and the end of the
rotary shaft has a crescent cam shape. Since the gravity force on the weight is larger than the centrifugal
force on the weight at the low cam gear revolution when starting, the crescent cam projects the cam
profile and lifts up the follower of the cam lifter, opens the intake valve.
FLYWEIGHT
CAMLIFTER
CRESCENT
CAM
ROTATION
Fig. 7-1
When the engine is running, the crescent cam is retracted into the camshaft profile because the centrifugal force applied onto the flyweight becomes larger than the gravity force and the decompression turns
OFF.
FLYWEIGHT
CAMLIFTER
CRESCENT
CAM
ROTATION
Fig. 7-2
7-2 INSPECTION
(1) When assembling the cam gear assembly, be sure that the spring hook is hooked on the flyweight.
(2) Be sure that the flyweight moves smoothly.
-
42
-
Page 47
8. CARBURETOR
8-1 OPERATION AND CONSTRUCTION
8-1-1 FUNCTIONS AND CONSTRUCTION OF THE DIAPHRAGM SYSTEM
This engine is equipped with a diaphragm type carburetor.
Since the fuel level is kept constant, irrespective of the tilting angle of the engine, it can be operated at
any position. The float chamber is provided with a diaphragm and is covered with a cover . When negative
pressure is generated in the air intake, the diaphragm bulges up, thereby pushing up the metering lever
and opening the inlet needle valve. When the negative pressure disappears, the spring forces the valve
shut. Therefore, fuel flow rate can be controlled by appropriately determining the diaphragm area and the
spring load.
AIR INTAKE
INLET NEEDLE VALVE
JET
DIAPHRAGM
ASSEMBLY
Fig. 8-1
FUEL
METERING LEVER
FUEL
-
43
-
Page 48
8-2 DISASSEMBLY AND REASSEMBLY
14
13
3
15
16
20
21
22
23
24
17
18
19
12
2
1
4
5
6
8
9
10
11
25
1. Screw
2. Plug
3. Swivel
4. Washer
5. Ring, spring retaining
6. Valve assembly, throttle
7. Body assembly, carburetor
8. O-ring
Fig. 8-2
9. Jet
10. Gasket, pump
11. Diaphragm, pump
12. Spring, pump
13. Body assembly, pump
14. Inlet screen
15. Metering lever spring
16. Metering lever pin
-
44
-
17. Inlet needle valve
18. Metering lever
19. Screw, metering lever pin
20. Metering diaphragm gasket
21. Diaphragm assembly, metering
22. Body assembly air purge
23. Primer pump
24. Primer pump cover
25. Screw
Page 49
8-2-1 PRECAUTIONS
(1) Wash the carburetor with clean gasoline before disassembly.
(2) Disassemble and reassemble the carburetor by referring to the exploded view.
(3) Refrain from disassembling the throttle valve assy. (6), pump body assy. (13) and the main body.
8-2-2 DISASSEMBLY AND REASSEMBLE PROCEDURES
(1) Removes the screw (25) and the primer pump cover (24). Remove dust or foreign matter stuck on the
primer pump (23), if any.
(2) Remove the pump body assy. (13) from the main body (Be careful not to lose the spring (15)).
Remove dust or foreign matter caught in the inlet screen (14), if any.
(3) Remove the jet (19) from the main body.
(4) Remove the screw (1) and remove the throttle valve assy. (6) from the main body.
(5) When assembling the carburetor, be sure that the jet (9) and the spring (12) are firmly installed.
8-2-3 PRECAUTIONS FOR INSPECTION
(1) Wash the main body with gasoline and blow it clean with compressed air.
(2) Check the jet for dust stuck on the surface, corrosion, etc. If there is dust stuck on the jet, wash it and
blow it clean with compressed air. If the jet is corroded, replace it with a new one. (NOTE : When
replacing a jet, be sure of using a new one with the same number).
(3) Check the gasket for deformation and damage. If it is deformed or damaged, change with a new one.
(4) The pump (diaphragm) should not be hardened nor damaged.
(5) The inlet valve and the outlet valve should be flat and not bent.
(6) The diaphragm assy. should be free of any hardening, damage or bent.
(7) After assembling the pump body assy.,check it for deformation of the metering lever and metering
spring, height of the metering lever, dust stuck on the inlet screen, valve leakage, etc. To check the
main check valve for correct operation, connect a vinyl or rubber hose to the check valve portion from
the jet side and breathe it with your mouth. If the valve stops when blown and closes when sucked,
the valve is working normally. If there is any abnormality , immerse it in gasoline for approximately 10
minutes and then blow and suck it repeatedly. If the valve can not be fixed even by doing so, replace
it with a new pump body assy.
(NOTE : Refrain from blowing the main check valve with compressed air. When using an air gun,
keep them approximately 30 cm apart of each other when the compressed air has a pressure of 6 kg/
2
cm
).
(8) Check the primer pump for any hole, damage or abnormal hardening. Be sure that the combination
valve is working normally.
-
45
-
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8-2-4 MARKS ON THE CARBURETOR
Marks are stamped as shown in the figure at the
right.
11
1 Model No.
11
22
2 Date of manufacture
22
Example
11
1 : 116 ---------- WYL116 (Walbro model No.)
11
22
2 : 914
22
week 14 (May. 29-Apr. 2)
1
1999
2
Fig. 8-3
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9. RECOIL STARTER
9-1 HOW TO DISASSEMBLE
The recoil starter rarely have problem under normal use. When it fails, however, or when greasing,
disassemble and reassemble it according to the following procedure.
Tools : Screwdriver and pincers (pliers)
(1) Remove the recoil starter from the engine.
(2) Pull out the starter knob, hold the rotary reel
with your thumb as shown in Figure 9-1 when
the reel notch gets aligned with the starter rope
outlet, and pull the starter rope to inside the
recoil starter with a screwdriver.
Hook the starter rope to the notch, and rewind
the reel to the arrow direction until it stops, by
controlling the rotation of the reel with your
thumb.
NOTCH
Fig. 9-1
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(3) Remove the parts as shown in Fig. 9-2.
Remove the reel slowly while turning it back and forth gently, otherwise the spiral spring may escase
from the case which may invite danger. (It the spiral spring escapes, put it in the case by following
procedure shown in Fig. 9-6.)
Untie the starter rope knot at the reel end and withdraw it to complete disassembling.
EH025
SET SCREW
EH035
SWING ARM
COLLAR
STARTER KNOB
REEL
SPIRAL SPRING
STARTER SHAFT
REEL
SPIRAL SPRING
SET SCREN
STARTER KNOB
Fig. 9-2
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9-2 HOW TO REASSEMBLE
(1) Pass the starter rope through the starter knob
and make an overhand knot as shown in Fig.
9-3. Pass the opposite side of the starter rope
from the starter case to the reel, and make a
knot in the same way, then put the rope end
securely into the rope housing in the reel.
Then, apply a small amount of grease on the
starter shaft and on the spiral spring.
(2) Check that the spring is securely set in the
reel and form the spring end to have 1 to 2
mm clearance between inner end of the spring
and the reel bush so that the inner end catches
the hook securely as shown in Fig. 9-4. The
shape of spring inner end (approx. 10 cm from
the end) can be adjusted with plier if neces-
sary.
(3) Prior to installing the reel in the starter case,
wind the starter rope to the reel in the arrow
direction of Figure 9-5, take out the third turn
of the starter rope from the reel notch and then
install the reel securely inside the starter case
so that the spiral spring inner end catches the
hook. Next, hold the starter rope as shown in
Figure 9-5, and rotate the reel 4 to 5 turns in
the arrow direction by utilizing the reel notch.
After winding the reel, hold it securely to pre-
vent it from reverse turn and pull out the starter
knob to stretch the rope tight and then release
the knob slowly. Rassemble the parts in re-
verse order of disassembling shown in Fig.
9-2. Tighten the setscrew securely.
REEL
APPLY
GREASE
REEL BUSH
Fig. 9-3
SPIRAL SPRING END
SPIRAL SPRING
1 to 2 mm
Fig. 9-4
APPROX.
10 mm
APPROX.
10 mm
INNER END
STARTER SHAFT
REEL
HOOK
*Be sure to check the following to make sure
that the parts are securely installed.
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49
Fig. 9-5
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Page 54
9-3 CHECK AFTER REASSEMBLE
(1) Pull the starter knob a few times to check if:
A. The starter knob is too heavy to pull, check that each part has been assembled as specified.
B. The ratchet fails to function, check is parts such as friction spring have been missing.
(2) Pull out the starter knob to extend the rope to its extreme to see if:
A. The starter rope still remains in the rope slot of the reel, unwind the rope by 1 to 2 turns as shown
in Fig. 9-1, as the spring may be over-stressed.
B. The starter rope is found weak to recoil or droops in halfway, apply grease or mobile oil to the
rotating part and to the friction parts. If it persists, wind-up the spring by 1 to 2 turns. (In this case,
check that the spring is not over-stressed.)
C. The spring escapes with a sound and the starter rope fails to spring back to its original position,
reassemble the starter from the beginning.
9-4 OTHER GUIDES
(1) When the spring escapes from the reel :
Make a ring having a rather small diameter
than spring housing using a thin wire.
Hook the outer end of the spring onto a part of
the ring and re-wind the spring into the wire
ring as shown in Fig.9-6 then put it into the
housing.
Remove the ring slowly while holding down
the spring to avoid getting out of place.
The ring can easily be removed by prying it
with the tip of a screwdriver.
Refer to Fig.9-4 for which way the spiral spring
must be placed.
(2) When it is lubricated :
WIRE RING
SPRING
Fig. 9-6
Lubricate the starter shaft and spring with a
grease (If possible, heat-resistant type is preferable) or a mobile oil when the starter is being disassembled and prior to long-term storage.
(3) When the swing arm does not move smoothly:
Apply grease (Alevin No. 3) or mobile oil on it.
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10. TROUBLESHOOTING
The following three conditions must be fulfilled for satisfactory engine start.
1. The cylinder filled with a proper fuel-air mixture.
2. Good compression in the cylinder.
3. Good spark, properly timed, to ignite the mixture.
The engine cannot be started unless these three conditions are met. There are also other factors which
make engine start difficult, e. g., a heavy load on the engine when it is about to start at low speed, and a
high back pressure due to a long exhaust pipe.
The most common causes of engine troubles are given below :
10-1 STARTING DIFFICULTIES
10-1-1 FUEL SYSTEM
(1) No gasoline in the fuel tank.
(2) The carburetor is not choked sufficiently especially when the engine is cold.
(3) Water, dust or gum in the gasoline interfering the fuel flow to the carburetor.
(4) Inferior grade gasoline or poor quality gasoline not vaporized enough to produce the correct fuel-air
mixture.
(5) If the carburetor overflows, excessive fuel runs into the cylinder when starting the engine, making the
fuel-air mixture too rich to burn. If this happens, remove the spark plug, and turn the starting pulley a
few turns in order to let the rich fuel-air mixture out of the spark plug hole into the atmosphere.
Keep the choke valve open during this operation.
Dry the spark plug well, screw it into place, and try to start again.
10-1-2 COMPRESSION SYSTEM
If starting difficulties and loss of power are not due to the fuel system or ignition system, the following
must be checked for possible lack of compression.
(1) Engine inside is completely dried up because of a long period of storage.
(2) Loose or broken spark plug. This causes a hissing noise made by mixture gas running out of cylinder
in compression stroke during cranking.
(3) Damaged head gasket or loose cylinder head. A similar hissing noise is produced during compres-
sion stroke.
(4) Incorrect Valve clearance
If the correct compression is not obtained even after remedying the above, disassemble the engine
and check further as follows :
a) Valve stuck open due to carbon or gum on the valve stem.
b) If the piston rings are stuck on the piston, remove the piston and connecting rod from the engine.
Clean or replace the parts.
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10-1-3 IGNITION SYSTEM
Check the followings for lack of spark.
(1) Wires of the ignition coil, spark plug or contact breaker disconnected.
(2) Ignition coil damaged and shorted.
(3) Spark plug cable wet or soaked with oil.
(4) Spark plug dirty or wet.
(5) Spark plug electrode gap incorrect.
(6) Spark plug electrode is connected or bridged.
(7) Incorrect spark timing.
10-2 ENGINE MISFIRES
(1) Incorrect spark plug electrode gap. Adjust it to anywhere between 0.7 and 0.8 mm.
(2) Ignition cable worn and leaking.
(3) Sparks weak.
(4) Ignition wire connections loose.
(5) Water in gasoline.
(6) Insufficient compression.
10-3 ENGINE STOPS
(1) Fuel tank empty. Water, dirt, gum, etc. in gasoline.
(2) Vapor lock, i. e., gasoline evaporating in the fuel lines due to overheat around the engine.
(3) Vapor lock in the fuel lines or carburetor due to the use of too volatile winter gas in the hot season.
(4) Air vent hole in the fuel tank cap plugged.
(5) Bearing parts seized due to lack of oil.
(6) Magneto or ignition coil faulty.
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10-4 ENGINE OVERHEATS
(1) Crankcase oil level low. Add oil immediately.
(2) Spark timing incorrect.
(3) Low grade gasoline is used, or engine is overloaded.
(4) Cooling air circulation restricted.
(5) Cooling air path misdirected causes loss of cooling efficiency.
(6) Cylinder head cooling fins clogged up with dirt.
(7) Engine operated in an enclosed space without sufficient cooling air.
(8) Exhaust gas discharge restricted, or carbon deposits in the combustion chamber.
(9) Engine running on low-octane gasoline detonates due to heavy load at low speed.
10-5 ENGINE KNOCKS
(1) Poor quality gasoline.
(2) Engine operating under heavy load at low speed.
(3) Carbon or lead deposits in the cylinder head.
(4) Spark timing incorrect.
(5) Loose connecting rod bearing due to wear.
(6) Loose piston pin due to wear.
(7) Curses of engine overheat.
10-6 ENGINE BACKFIRES THROUGH CARBURETOR
(1) Water or dirt in gasoline, or low-grade gasoline.
(2) Intake valve stuck.
(3) Valves overheated, or hot carbon particles in the combustion chamber.
(4) Engine cold.
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11. INSTALLATION
Engine life, ease of maintenance and inspection, frequency of checks and repairs, and operating cost all
depend on the way in which the engine is installed. Review the following instructions carefully for installing the engine.
11-1 INSTALLING
When mounting the engine, carefully examine its position, the method of connecting it to a machine, the
foundation, and the method of supporting the engine.
When determining its mounting position, in particular, make sure that gasoline and oil can easily be
supplied and checked, the spark plug can easily be checked, the air cleaner can easily be serviced, and
that the oil can easily be discharged.
11-2 VENTILATION
Fresh air is necessary for cooling the engine and burning the fuel.
In the case the engine is operated under a hood or in a small room, temperature rise in the engine room
can cause vapor lock, oil deterioration, increased oil consumption, loss of power, piston seizure, shorter
engine life, etc., making it impossible to operate the engine properly . It is necessary, therefore, to provide
a duct or baffle to guide cooling air to the engine to prevent recirculation of the hot air used for engine
cooling, and temperature rise of the machine. Keep the engine room temperature below 50°C even in the
hottest period of the year.
11-3 EXHAUST GAS DISCHARGE
Exhaust gas is noxious. When operating the engine indoors, be sure to discharge the exhaust gas
outdoor. If a long exhaust pipe is used in such a case, the internal resistance increases causing loss of
engine power. Thus pipe inside diameter must be increased in proportion to exhaust pipe length.
Exhaust pipe : Less than 3 m long, pipe inside diameter 30 mm ,
Less than 5 m long, pipe inside diameter 33 mm.
11-4 POWER TRANSMISSION TO DRIVEN MACHINES
11-4-1 BELT DRIVE
Take the following notes into consideration.
* V-belts are preferable to flat belts.
* The driving shaft of the engine must be parallel to the driven shaft of the machine.
* The driving pulley of the engine must be in line with the driven pulley of the machine.
* Install the engine pulley as close to the engine as possible.
* If possible, span the belt horizontally.
* Disengage the load when starting the engine.
If no clutch is used, use a belt tension pulley or the like.
11-4-2 FLEXIBLE COUPLING
When using a flexible coupling, run out and misalignment between the driven shaft and engine shaft
must be minimized. Run out and misalignment tolerance are specified by the coupling manufacturer.
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12. SERVICE DATA
12-1 CLEARANCE DATA AND LIMITS
Unit : mm (in)
CYLINDER
*Valve guide inside dia.
*Inside dia.
ITEM
EH025
EH035
STD
EH025
EH035
STD Limit
3.005 - 3.025
(0.118 - 0.119)
3.505 - 3.525
(0.138 - 0.139)
34.00 - 34.02
(1.3386 - 1.3394)
39.00 - 39.02
(1.5354 - 1.5362)
3.1
(0.122)
3.6
(0.142)
34.06
(1.3409)
39.06
(1.5378)
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Unit : mm (in)
ITEM
PISTON
* Piston size (At skirt in thrust direction)
*Ringgroove side clearance
8.2 mm
-
4.5
STD
2nd
Oil ring
EH025
EH035
Top
EH025
EH035
STD Limit
33.959
(1.3370
38.959
(1.5338
-
33.980
-
1.3378)
-
38.980
-
1.5346)
0.03 - 0.07
(0.0012 - 0.0028)
0.02 - 0.06
(0.0008 - 0.0024)
0.03 - 0.07
(0.0012 - 0.0028)
0.04 - 0.14
(0.0016 - 0.0055)
33.940
(1.3362)
38.940
(1.5331)
0.12
(0.005)
0.12
(0.005)
0.20
(0.008)
* Piston pin hole
* Piston pin outside dia.
* Piston ring end gap
EH025
EH035
EH025
EH035
Top
2nd
EH025
EH035
EH025
EH035
7.996 - 8.005
(0.3148 - 0.3152)
9.996 - 10.005
(0.3935 - 0.3939)
7.994 - 8.000
(0.3147 - 0.3149)
9.994 - 10.000
(0.3935 - 0.3937)
0.1-0.25
(0.0039-0.0098)
0.1 - 0.25
(0.0039 - 0.0098)
8.03
(0.3161)
10.03
(0.3949)
7.988
(0.3145)
9.988
(0.3932)
0.8
(0.0315)
0.8
(0.0315)
Oil
ring
-
EH025
EH035
56
-
0.1 - 0.6
(0.0039 - 0.0236)
0.8
(0.0315)
Page 61
Unit : mm (in)
CAMSHAFT
*Cam height (IN. and EX.)
* Journal outside dia.
D
2
VALVE
*Valve stem outside dia.
ITEM
STD Limit
EH025
23.20 - 23.30
(0.9134 - 0.9173)
EH035
D
1
EH025
D
1
EH035
EH025
D
2
EH035
EH025
5.01 - 5.06
(0.1972 - 0.1992)
4.99 - 5.00
(0.1965 - 0.1969)
2.975 - 2.990
(0.1171 - 0.1177)
IN.
EH035
EH025
3.475 - 3.490
(0.1368 - 0.1374)
2.950 - 2.965
(0.1161 - 0.1167)
EX.
EH035
3.450 - 3.465
(0.1358 - 0.1364)
22.65
(0.8917)
-----------
-----------
2.9
(0.1142)
3.4
(0.1339)
2.9
(0.1142)
3.4
(0.1339)
*Clearance between valve stem dia. and valve
guide.
*Valve clearance
*Valve lift
*Valve spring free length (IN. and EX.)
IN.
EX.
IN. / EX.
(cold)
IN. / EX.
EH025
EH035
EH025
EH035
EH025
EH035
0.015 - 0.050
(0.0006 - 0.0020)
0.017 - 0.050
(0.0007 - 0.0020)
0.040 - 0.075
(0.0016 - 0.0030)
(0.0051 - 0.0067)
3.0 - 3.2
(0.1181 - 0.1260)
17.7
(0.6969)
21.0
(0.8268)
0.2
(0.0079)
0.2
(0.0079)
0.13 - 0.17
2.6
(0.1024)
-----------
-----------
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12-2 TORQUE SPECIFICATIONS
Tightening Torque
ITEMS
N-m Kg-cm ft-lb.
Retainer plate (Crankcase) 3 - 4 30 - 40 2.2 - 2.9
Cylinder block (Crankcase) 4.5 - 6.5 45 - 65 3.3 - 4.7
Oil case (Crankcase) 4 - 5.5 40 - 55 2.9 - 4.0
Cam gear cover 4 - 5.5 40 - 55 2.9 - 4.0
Ignition coil 2 - 4 20 - 40 1.4 - 2.9
Flywheel 9 - 12 90 - 120 6.5 - 8.8
Clutch 7.5 - 10 75 - 100 5.4 - 7.2
Rocker arm (adjust screw) 5 - 6.5 50 - 65 3.6 - 4.7
Rocker cover 4 - 5.5 40 - 55 2.9 - 4.0
Muffler 7 - 9 70 - 90 5.1 - 6.5
Muffler cover 3 - 5 30 - 50 2.2 - 3.6
Insulator carburetor
(insulator&crankcase)
Recoil starter 1 - 2.5 10 - 25 0.7 - 1.8
Blower housing (engine cover) 2 - 4 20 - 40 1.4 - 2.9
Spark plug 9 - 13 90 - 130 6.5 - 9.4
Cover (air cleaner) 0.5 - 1 5 - 10 0.04 - 0.7
Air cleaner plate 2 - 4 20 - 40 1.4 - 2.9
Pulley 4 - 5.5 40 - 55 2.9 - 3.9
Plug cover EH035 1.5 - 3 15 - 30 1.1 - 2.2
4 - 5.5 40 - 55 2.9 - 4.0
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12-3 OIL GRADE CHART
Use oil classified SF or higher.
Multi-grade oil tends to increase its consumption at high ambient temperature.
Comparison between oil viscosity and temparature
5W
10W
Specified
Lubricant
Quality
Single
grade
Multi-
grade
20W
#20
#30
#40
10W-30
10W-40
20W-40
-
-
20
4
-
10
14
32
0
10
50
20
68
30
86
40 °C
104 °F
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Page 64
13. MAINTENANCE AND STORAGE
The following maintenance jobs apply when the engine is operated correctly under normal conditions.
The indicated maintenance intervals are by no means guarantees for maintenance free operations during these intervals.
For example, if the engine is operated in extremely dusty conditions, the air cleaner should be cleaned
every day instead of every 50 hours.
13-1 DAILY MAINTENANCE
MAINTENANCE ITEMS REMARKS
1) Clean away dust and chaff from engine. Governor linkage is especially sensitive to dust.
2) Check fuel leakage from fuel system. If any,
retighten fasteners or replace necessary parts.
3) Inspect for loose hardware and retighten if
necessary.
4) Check oil level and add up to full mark.
Loose bolts and nuts may come off and result in
breakage of other parts.
13-2 INITIAL 20 HRS. MAINTENANCE
MAINTENANCE ITEMS REMARKS
1) Change crankcase oil. To remove sludge from run-in operation.
13-3 EVERY 50 HRS. (10 DAYS) MAINTENANCE
MAINTENANCE ITEMS REMARKS
1) Change crankcase oil. Contaminated oil quickens wear.
2) Clean air cleaner.
3) Check and clean spark plug.
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13-4 EVERY 100-200 HRS. (MONTHLY) MAINTENANCE
SMETIECNANETNIAMSKRAMER
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13-5 ENGINE STORAGE
(1) Perform the above 13-1 and 13-2 maintenance jobs.
(2) Drain fuel from the fuel tank and carburetor.
(3) To prevent rust in the cylinder bore, apply oil through the spark plug hole and turn the crankshaft
several turns by hand. Reinstall the plug.
(4) Turn the starting pulley by hand and leave it where the resistance is the heaviest.
(5) Clean outside of the engine with oiled cloth.
(6) Put a plastic cover or the like over the engine and store the engine in dry place.
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PRINTED IN THE USA
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