TOHATSU MFS 4D User manual

SERVICE
MANUAL
4 STROKE
MFS 4D
MFS 5D
MFS 6D
Models
OB No.003-21034-4BA1｜04-21 NB

i
4st 4/5/6 2020
Introduction
Before reading this manual
This service manual provides information that is needed for inspection, service and repair of
applicable outboard motors. For information about operation of the products that are not described in
this document, refer to the owners manual. For our customers' safe and dependable use of the
product for long term, it is essential to maintain the performance and quality of the outboard. To
ensure this, the maintenance and service have to be done properly by service technicians with
fundamental knowledge and skills. This manual is utilized so that our customers can always use their
outboard motor with full satisfaction.
Safety Information
Safety Statements
The following safety statements are found throughout this manual and indicate information
which, if ignored, could result in fatal safety hazards or property damage:
Attention:
WARNING
Indicates the presence of a hazard or an
unsafe activity which, if ignored, could
result in severe injury or death.
DANGER
Indicates the presence of a hazard which, if
ignored, will result in severe injury or
death.
CAUTION
Indicates the presence of a hazard or an
unsafe activity which, if ignored, could
result in minor personal injury or damage to
the products or facilities.

ii 4st 4/5/6 2020
Lower Unit
7) Disassembly of Propeller Shaft Housing
1. Remove bearing 1by using commercially available bearing
puller.
2. Remove oil seal 2.
1Bearing Do not reuse.
8) Inspection of Propeller Shaft Housing
1. Use cleaning oil and cleaning brush to clean propeller shaft
housing, and check it for crack or damage. Replace if
necessary.
2. Check reverse (C) gear teeth and clutch for crack or
damage. Replace if necessary.
2Oil Seal Do not reuse.
CAUTION
Do not reuse removed bearing.
Before removing, check bearing for play or
deflection. Replace if necessary.
When reusing bearing without removing it, check
it for play or deflection. Replace if necessary.
1
2
P/C Fig. 8
A
B
Sail Pro A
B
1
2
34
5
6
7
13
14
15
16
17 18
19
20
21
22
23
24
25
26
27
28
29
30
31
30a
32
30a
34
35
36
37
38
39
40
41
42
43
44
45 46
47
48
50
51
52
53
54 55
56
61
3
4
8
9
10
11
12
33
49
57 60
58
59
62
63 64
65
GREASE
OBMOBM
OBM
OIL
GEARGEAR
GEAR
GREASE
OBMOBM
OBM
OIL
GEARGEAR
GEAR
TEF
GREASE
TEF
6 N·m (4 lb·ft) [0.6 kgf·m]
OIL
GEARGEAR
GEAR
GREASE
OBMOBM
OBM
LIT
GREASE
LIT
13 N·m (9 lb·ft) [1.3 kgf·m]
GREASE
OBMOBM
OBM
GREASE
OBMOBM
OBM
GREASE
OBMOBM
OBM
LIT
GREASE
LIT
OIL
GEARGEAR
GEAR
Gear Case (Drive Shaft) • Gear Case (Propeller Shaft)
TEF
GREASE
TEF
GREASE
OBMOBM
OBM
OIL
GEARGEAR
GEAR
LIT
GREASE
LIT
Lower Unit
6
Ref.
No. Description Q'ty Remarks
1-1 Gear Case Assy 1 STD
1-2 Gear Case Assy 1 for Sail Pro
2 Roller Bearing 14-20-12 1
3 Plug 8-8 2
4 Gasket 2 Do not reuse.
5 Anode 1
6 Bolt 1 M6 L=16mm
7 Ball Bearing 6004 1
8 Propeller Shaft Housing Assy 1
9 Propeller Shaft Housing 1
10 Oil Seal 15-28-10 1
11 O-Ring 3.2-47 1 Do not reuse.
12 Ball Bearing 6002 1
13 Bevel Gear Assy (A) 1
14 Bevel Gear B 1
15 Bevel Gear Assy (C) 1
16 Washer 15.2-19-1.9 1
17-1 Shim 21-28-0.1 A
17-2 Shim 21-28-0.15 A
18 Propeller Shaft 1
19 Clutch 1
20 Pin 3.5-28 1
21 Spring 1
22 Spring Retainer 1
23 Push Rod 1
24 Water Strainer 1
25 Screw 1 M6 L=20mm
26 Water Pipe (Lower) 1
27 Seal 2
28 Water Pump Impeller 1
29 Key φ2-11 1 Pump Impeller
30 Pump Case (Upper) 1
30a Dowel Pin 2
31 Pump Case Liner 1
32 Water Pump Guide Plate 1
33 Pump Case Gasket 1 Do not reuse.
34 Guide Plate Gasket 1 Do not reuse.
35 Bolt 4 M6 L=45mm
36 Washer 4 M6
37 Pump Case (Lower) 1
38 Oil Seal 10-24-8 1
39-1 Shim 26.5-34.8-0.1 A
39-2 Shim 26.5-34.8-0.15 A
40 Pump Case Gasket (Lower) 1 Do not reuse.
41 Bolt 1 M6 L=25mm
42 Water Pipe Seal (Lower) 1
Lower Unit
1. Special Tools
Removing spring pin
Spring Pin Tool A
P/N. 345-72227-0
Installing spring pin
Spring Pin Tool B
P/N. 345-72228-0
Used in combination with driver rod and
bearing attachment to locate lower gear
case bearing
Center Plate
P/N. 3AB-99701-0
Used in combination with center plate and
bearing attachment
Driver Rod
P/N. 3AB-99702-0
Installing bearings
Bearing Attachment
P/N. 3BV-99905-0
Installing bearings
Needle Bearing Press Kit
P/N. 369-72900-0
Measuring gap between forward and
pinion gears (A and B gears)
Backlash Measuring Tool Kit
P/N. 369-72740-0
Measuring backlash
Clamp A
P/N. 3B7-72720-0
Used to attach dial gauge
when measuring backlash
Dial Gauge Plate
P/N. 3B7-72729-0
1
2
3
45
6
About this manual
This service manual is designed so that service persons are able to perform their work correctly.
Understand the following matters well for efficient repairs.
1Each chapter begins with the introduction of special tools that are used for the work described in the chapter so that
the service persons are able to understand the tools needed.
2Parts that are serviced in each chapter and their details are presented by using a component composition
diagram.
3Fastening torques are described in the component composition diagram and in the body text and are
critical points of the applicable repair.
4Pictograms indicate that there is an important instruction for the relevant parts. It also shows the type of
lubricant and its application point(s).
5The component composition diagrams describe the names of the parts, the quantity of the parts used,
size of fasteners and special notes.
6Specific works are described in detail by using illustrations and adding advice on the work.

iii
4st 4/5/6 2020
Example : <Pressure>
Conventional system (kilo-gram meter unit)
Conventional system (US pound inch unit)
SI unit (1 kgf/cm2= 0.0980665 MPa)
* Measurements are shown using SI unit followed by conventional units (US unit) and [Japanese domestic unit].
0.90 MPa (128 psi) [9.0 kgf/cm2]
Example : <Torque>
*
* The conventional unit for measurement of force uses "kgf (kilogram force)" to discriminate it from
"kg (mass kilogram)" of SI unit system.
18 N·m (13lb·ft) [1.8 kgf·m]
Example : <Volume>
900 mL (30.4 fl.oz)
Example : <Length>
10 mm (0.39 in)
This manual uses SI unit system (International System of Units) for pressure, force (load), torque and stress. In
this manual, the main units are as follows.
<Reference>
What is the SI unit system?
Although the measurement unit is standardized mostly with metric system in the world, the metric system
includes different kinds of unit systems.
Though the metric system was established expecting that a single unit system would be used in the world,
various physical units were established later, resulting in branching the metric system in different unit
systems.
The new unit system is called "International System of Units"because it was established for the purpose of
unifying the different unit systems.
Since the metric system was initially established in France, and International Bureau of Weights and
Measures (IBWM) is located in Paris, General Conference of Weights and Measures (GCWM) passed a
resolution of the international unit system as "Systéme International d'Unités (French)" that is abbreviated as
"SI unit".
For example, conventional metric system uses the unit of mass (kg) and unit of force (kg or kgf) without
discriminating them, but the SI unit system uses, for example, "kg"as the unit of mass, and "N"as the unit of
force, aiming to apply a kind of unit for a kind of physical quantity.

4st 4/5/6 2020
iv
Description of Pictograph
OIL RPM
O Kr/min
ADH
17411741
G17G17
BOND
G103G103
BOND
TB
13421342
OIL-COMP.
SOC
SOC
OIL
GEARGEAR
GREASE
OBM
OBM
4st
OIL
LIT
GREASE
TEF
GREASE
GREASE
RUB
Maintenance
Service
Information Service Data
Specified
Electrical
Value
Lubrication
Oil
Fuel System
(Carburetor)
Special Tool
Specified
Measurement
Value
Lower Unit Electrical
System
Power Unit
Troubleshooting
Tightening
Torque
Accessories Wiring
Diagrams
Bracket
The following symbols represent the contents of individual chapters.
The following symbols indicate items needed for the service.
Specified Part
Test Run
Adjustment
Engine RPM
Use Limit
4 stroke
Engine Oil Gear Oil Waterproof
Grease
Low
Temperature
Resistant
Lithium
Grease
[Konishi Bond]
• G103
Rubber Grease
RUB
[Konishi Bond]
• G17
The following symbols indicate a point to which lubrication oil, sealing agent or screw-locking agent is to be applied.
Teflon® Grease
TEFLON
Screw Lock
Agent
[Three Bond®]
• 1342
Instant
Adhesive
[Three Bond®]
• 1741
Oil Compound
[Shinetsu Silicon]
S.O.C

4st 4/5/6 2020 v
1.Service Information
1. Identification
(Engine Serial Number) ……………… 1-2
2. Work Safety ……………………………… 1-2
1) Fire Prevention …………………………… 1-2
2) Ventilation ………………………………… 1-2
3) Protection ………………………………… 1-2
4) Genuine Parts …………………………… 1-2
5) Tools ……………………………………… 1-3
6) Recommendations on Service ………… 1-3
7) Cautions in Disassembling and
Assembling Components ………………… 1-4
3. Tools and Instruments ………………… 1-5
1) Test Propeller ……………………………… 1-5
2) Instruments………………………………… 1-5
3) Special Tools ……………………………… 1-6
4. Pre-delivery Inspection ……………… 1-8
1) Steering Handle…………………………… 1-8
2) Gear Shift ………………………………… 1-8
3) Engine Oil ………………………………… 1-8
4) Gear Oil …………………………………… 1-8
5) Fuel Tank Line …………………………… 1-9
6) Rigging …………………………………… 1-9
7) Inspection of Tilt Stopper ………………… 1-9
8) Inspection of Stop Switch………………… 1-10
9) Cooling Water Check Port ……………… 1-10
10) Idle Operation……………………………… 1-10
11) Propeller Selection ……………………… 1-11
12)
Inspection of Forward and Reverse Shifts ……… 1- 11
5. Break-in Operation ……………………… 1- 12
6. Test Run …………………………………… 1- 12
7. Checks After Test Run ………………… 1- 13
2.Service Data
1. Outline Dimensions …………………… 2-2
1) Engine Dimensions ……………………… 2-2
2) Clamp Dimensions ……………………… 2-4
2. Engine Lubrication System
Diagram …………………………………… 2-5
3. Cooling Water System Diagram
Specifications …………………………… 2-6
5. Maintenance Data ……………………… 2-10
6. Tightening Torque Specifications … 2-14
7. Sealant and Lubricant ………………… 2-15
3.Maintenance
1. Special Tools ……………………………… 3-2
2. Inspection Schedule …………………… 3-3
3. Inspection Items ………………………… 3-4
1) Inspection of Top Cowl …………………… 3-4
2) Fuel System ……………………………… 3-4
3) Inspection of Fuel Tank…………………… 3-5
4) Inspection of Fuel Filter ………………… 3-5
5) Replacement of Engine Oil ……………… 3-6
6) Inspection of Gear Oil Quantity ………… 3-7
7) Inspection of Water Pump ……………… 3-7
8) Replacement of Gear Oil ………………… 3-9
9) Inspection of Gear Case (for leakage) …… 3- 10
10) Inspection of Spark Plug ………………… 3-11
11) Inspection of Compression Pressure …… 3-12
12) Inspection and Adjustment of
Valve Clearance…………………………… 3-13
13) Throttle Cable……………………………… 3-15
14) Inspection of Idle Engine Speed ………… 3-17
15) Inspection of Ignition Timing …………… 3-17
16) Inspection of Anode ……………………… 3-18
17) Replacement of Anode …………………… 3-18
18) Inspection of Propeller …………………… 3-19
19) Inspection of Thermostat ………………… 3-19
20)
Inspection of Cooling Water Passage …… 3- 20
21) Flushing with Water ……………………… 3-21
22) Greasing Points …………………………… 3-22
4.Fuel System
1. Special Tools ……………………………… 4-2
2. Parts Layout ……………………………… 4-3
Fuel Tank ……………………………………… 4-3
Carburetor • Fuel Pump……………………… 4-4
Integral Fuel Tank …………………………… 4-6
3. Carburetor Inner Passages ………… 4-8
1) Idling Passage …………………………… 4-8
2) Off-Idle Passage ………………………… 4-9
3) High Speed Passage …………………… 4-10
4) Choking Passage ………………………… 4-11
4. Inspection Items ………………………… 4-12
1) Inspection of Fuel Feed System Piping … 4-12
2) Draining Fuel ……………………………… 4-12
3) Inspection of Fuel Tank and
Fuel Tank Cap …………………………… 4-13
4) Inspection of Fuel Cock ………………… 4-13
5) Inspection of Fuel Filter ………………… 4-13
6) Removing Carburetor …………………… 4-15
7) Disassembling Carburetor ……………… 4-16
8) Inspection and clean of Carburetor …… 4-17
9) Inspection of Fuel Connector …………… 4-18
10) Assembling of Carburetor ……………… 4-18
11) Adjustment of Float Height ……………… 4-19
12) Installing Carburetor ……………………… 4-19
13) Removing Fuel Pump …………………… 4-20
14) Disassembly and Inspection of
Fuel Pump ………………………………… 4-20
15) Assembly of Fuel Pump ………………… 4-21
5.Power Unit
1. Special Tools ……………………………… 5-2
2. Parts Layout ……………………………… 5-3
Engine ………………………………………… 5-3
Magneto ……………………………………… 5-4
Cylinder & Oil Pan …………………………… 5-6
Cylinder Head & Valve & Camshaft………… 5-10
Piston & Crankshaft ………………………… 5-12
Recoil Starter ………………………………… 5-13
Top Cowl ……………………………………… 5-14
3. Inspection Items ………………………… 5-15
1) Inspection of Compression Pressure …… 5-15
2) Inspection of Valve Clearance…………… 5-16
3) Removing Power Unit …………………… 5-18
4) Removal and Disassembly of
Crank Case Head ………………………… 5-19
5) Inspection of Crank Case Head ………… 5-20
6) Assembly of Crank Case Head ………… 5-20
7) Installation of Crank Case Head ………… 5-21
8) Disassembly of Power Unit ……………… 5-21
9) Removal of Rocker Arm ………………… 5-24
10) Removing Cylinder Head ………………… 5-25
11) Inspection of Rocker Arm and Pivot …… 5-25
12) Inspection of Push Rod Plate …………… 5-26
13) Inspection of Push Rod ………………… 5-26
14) Disassembly and Inspection of
Oil Pump …………………………………… 5-26

4st 4/5/6 2020
vi
15) Disassembly of Cylinder and Oil Pan…… 5-28
16) Disassembly and Inspection of
Breather Chamber………………………… 5-30
17) Inspection of Lifter………………………… 5-30
18) Inspection of Camshaft…………………… 5-31
19) Inspection of Piston Outer Diameter …… 5-32
20) Inspection of Cylinder Inner Diameter…… 5-32
21) Inspection of Piston Clearance ………… 5-32
22) Inspection of Piston Ring
Side Clearance …………………………… 5-33
23) Inspection of Piston Rings ……………… 5-33
24) Inspection of Piston Pin ………………… 5-34
25) nspection Connecting Rod Small End
Inner Diameter …………………………… 5-34
26) Inspection of Connecting Rod Big End
Inner Diameter …………………………… 5-34
27) Inspection of Connecting Rod Big End
Side Clearance …………………………… 5-35
28) Inspection of Crankshaft ………………… 5-35
29) Disassembly and Inspection of Oil Pan … 5-36
30) Removal of Valves and Springs ………… 5-37
31) Inspection of Valve Springs ……………… 5-37
32) Inspection of Valve ……………………… 5-38
33) Inspection of Valve Guide ……………… 5-38
34) Inspection of Valve Seat ………………… 39
35) Correction of Valve Seat ………………… 5-40
36) Installation of Valves ……………………… 5-43
37) Installation of Piston and
Connecting Rod…………………………… 5-44
38) Assembly of Cylinder Oil Pan …………… 5-45
39) Installation of Cylinder Head …………… 5-47
40) Installing Flywheel………………………… 5-49
41) Installation of Power Unit ………………… 5-52
6.Lower Unit
1. Special Tools ……………………………… 6-2
2. Parts Layout ……………………………… 6-4
Drive Shaft Housing ………………………… 6-4
Gear Case (Drive Shaft) • Gear Case
(Propeller Shaft) ……………………………… 6-6
3. Inspection Item ………………………… 6-10
1) Draining Gear Oil ………………………… 6-10
2) Removing Propeller ……………………… 6-10
3) Removing Lower Unit …………………… 6-11
4) Disassembly of Water Pump …………… 6-11
5) Inspection of Water Pump ……………… 6-12
6) Removing Propeller Shaft Housing Ass'y…… 6- 13
7) Disassembly of Propeller Shaft Housing …… 6- 14
8) Inspection of Propeller Shaft Housing ……… 6- 14
9) Assembly of Propeller Shaft Housing…… 6-15
10) Removing Drive Shaft …………………… 6-15
11) Disassembly of Propeller Shaft Ass'y …… 6- 16
12) Inspection of Propeller Shaft …………… 6-16
13) Assembly of Propeller Shaft Ass'y ……… 6-16
14) Removing Clutch Cam and Cam Rod … 6-17
15) Disassembly of Clutch Cam and
Cam Rod…………………………………… 6-17
16) Inspection of Clutch Cam and Cam Rod …… 6- 17
17) Assembly of Clutch Cam and Cam Rod …… 6- 18
18) Removing Pump Case (Lower) ………… 6-18
19) Disassembly of Pump Case (Lower) …… 6-18
20) Assembly of Pump Case (Lower) ……… 6-18
21) Inspection of Drive Shaft ………………… 6-19
22) Inspection of Pinion (B) Gear and
Forward (A) Gear ………………………… 6-19
23) Disassembly of Gear Case ……………… 6-20
24) Inspection of Gear Case ………………… 6-21
25) Assembly of Gear Case ………………… 6-21
26) Installation of Forward Gear and
Pinion Gear (A and B Gears) …………… 6-22
27) Reassembly of Pump Case (Lower) …… 6-22
28) Installation of Clutch Cam and Cam Rod…… 6- 22
29) Determination of forward (A) gear
backlash …………………………………… 6-23
30) Installation of Water Pump ……………… 6-25
31) Installation of Propeller Shaft Housing ……… 6- 26
32) Filling with Gear Oil ……………………… 6-27
33) Installation of Lower Unit ………………… 6-27
7.Bracket
1. Parts Layout ……………………………… 7-2
Bracket • Reverse Lock……………………… 7-2
Drive Shaft Housing • Shift ………………… 7-4
Bottom Cowl • Tiller Handle ………………… 7-6
Top Cowl ……………………………………… 7-10
2. Disassembling and
Assembling Procedure……………………… 7-11
1) Removal and Inspection of
Drive Shaft Housing ……………………… 7-11
2) Removal and Inspection of Clamp
Bracket …………………………………… 7-13
3) Installation of Clamp Bracket and
Drive Shaft Housing ……………………… 7-14
4) Removal, Inspection and Installation of
Water Pipe ………………………………… 7-16
5) Remove, Inspection and Installation of
Tiller Handle ……………………………… 7-17
6) Adjustment of Throttle Cable …………… 7-20
8.Electrical System
1. Special Tools ……………………………… 8-2
2. Parts Layout ……………………………… 8-4
Magneto ……………………………………… 8-4
3. Ignition System and
Ignition Control System ……………… 8-6
1) Inspection of Ignition Spark ……………… 8-6
2) Inspection of Plug Cap …………………… 8-7
4) Inspection of Stop Switch………………… 8-9
5) Inspection of Oil Pressure Switch ……… 8-9
6) Inspection of Rectifier …………………… 8-10
7) Inspection of Lighting Coil ……………… 8-10
9.Troubleshooting
1. Troubleshooting List …………………… 9-2
2. Power Unit ………………………………… 9-3
1 Engine will not start or is a little hard to start.
(Recoil starter operates normally.) ………… 9-3
2 Engine starts but stalls soon. …………… 9-5
Fuel System ……………………………… 9-5
Ignition System …………………………… 9-6
Intake • Compression Pressure ………… 9-7
3 Idle engine speed will not stabilize. …… 9-8
4 Rough acceleration. ……………………… 9-9
5 Gear shifting cannot be made
normally. …………………………………… 9-10
10.Wiring Diagram

4st 4/5/6 2020 vii
1
2
3
4
5
6
7
8
9
10
Service Information
Service Data
Inspections and
Adjustments
Fuel System
Power Unit
Lower Unit
Bracket
Electrical System
Troubleshooting
Wiring Diagram
INDEX
O K

4st 4/5/6 2020
viii

1
Service Information
1
1. Identification
(Engine Serial Number) ……………… 1-2
2. Work Safety ……………………………… 1-2
1) Fire Prevention …………………………… 1-2
2) Ventilation ………………………………… 1-2
3) Protection ………………………………… 1-2
4) Genuine Parts …………………………… 1-2
5) Tools ……………………………………… 1-3
6) Recommendations on Service ………… 1-3
7) Cautions in Disassembling and
Assembling Components ………………… 1-4
3. Tools and Instruments ………………… 1-5
1) Test Propeller ……………………………… 1-5
2) Instruments………………………………… 1-5
3) Special Tools ……………………………… 1-6
4. Pre-delivery Inspection ……………… 1-8
1) Steering Handle…………………………… 1-8
2) Gear Shift ………………………………… 1-8
3) Engine Oil ………………………………… 1-8
4) Gear Oil …………………………………… 1-8
5) Fuel Tank Line …………………………… 1-9
6) Rigging …………………………………… 1-9
7) Inspection of Tilt Stopper ………………… 1-9
8) Inspection of Stop Switch………………… 1-10
9) Cooling Water Check Port ……………… 1-10
10) Idle Operation……………………………… 1-10
11) Propeller Selection ……………………… 1-11
12)
Inspection of Forward and Reverse Shifts ……… 1- 11
5. Break-in Operation ……………………… 1- 12
6. Test Run …………………………………… 1- 12
7. Checks After Test Run ………………… 1- 13

1-2
Service Information
4st 4/5/6 2020
1. Identification (Engine Serial Number)
Engine serial number is located on the swivel bracket.
2. Work Safety
1) Fire Prevention
Gasoline is hazardous material and very flammable. Do not
handle gasoline near ignition source such as spark or static
electricity.
2) Ventilation
Exhaust gas or gasoline vapor is hazardous. Be sure to
ventilate well when working indoors.
3) Protection
Wear a pair of goggles, working gloves and safety shoes to
protect skin from chemicals and oil and your eyes from
particles generated by grinding or polishing. Avoid contact of
oil, grease or sealing agent to the skin. In case of exposure
to such matters, wash away with soap or warm water
immediately.
4) Genuine Parts
Use parts and/or chemicals that are genuine items or
recommended.
2
1
3XXXXXX
4.41 kW - 5500 r/min
25.6 - 27.1 kg
3JE
MFS6DD
1 Model Name
2 Model Type
3 Serial Number

1-3
1
4st 4/5/6 2020
5) Tools
Use specified special tools to prevent damaging to parts and
to perform work safely and surely. Be sure to follow
installation procedures and specified torque described in this
manual.
6) Recommendations on Service
Remove foreign substances and dirt from outboard motor
and individual parts by cleaning. Apply recommended oil or
grease to rotating areas and sliding surfaces. After carrying
out each work, always conduct a check to ensure smooth
movement and sealing.
3R0728150
3AC728710

1-4
Service Information
4st 4/5/6 2020
LIT
GREASE
LIT
Power Unit Work Board (mm)
ø60
170
20
70
70
120
120
15
30
30
30 50
35
35
7) Cautions in Disassembling and
Assembling Components
(1) Secure outboard motor to a dedicated stand.
(2) Replace parts that cannot be reused such as packings,
gaskets, O-rings, oil seals, spring pins or split pins with new
ones after disassembly. Replace deformed snap rings with
new ones.
(3) Replace parts such as packings, gaskets, O rings, oil seals,
spring pins or split pins with new ones after they are
removed. Replace deformed snap rings with new ones.
(4) When replacing parts, be sure to use genuine parts. For
fluids such as gear oil, use genuine product.
(5) Be sure to use special service tools, and perform the work
properly.
(6) When reassembling parts, use their mating marks. For parts
without mating marks, simple marking makes reassembling
easier. Use applicable parts list for reference.
(7) Clean individual parts that have been removed, and check
their condition.
(8) When reassembling parts, pay extra attention to details such
as the fitting of each part, repair limits, air tightness, clogging
of oil holes for lubrication and greasing, packings, wiring,
piping and so on. For components which use a lot of bolts
and nuts for assembly, such as the cylinder head and
crankcase, tighten all the fasteners uniformly to their
specified torques clockwise in two or three stages, starting
with the inner ones first followed by the outer ones.
(Reverse the order when disassembling.)
(9) When installing bearings, the flat (numbered) side should be
the side in contact with the special assembly tool.
(10) When installing oil seals, be careful not to scratch the
surface of the lip that contacts with the shaft, and install
them in correct direction. Apply recommended grease to the
lip before installation.
(11) When applying liquid packing, be extra careful of the
thickness and quantity. Excess liquid may ooze out if too
much liquid is applied, adversely affecting the interior of the
crankcase. Use adhesives after thoroughly reading the
instructions.
(12) When servicing power unit, use of wood work board makes
the work easier.
1
SOC
OIL-COMP.
GM
SOCSOC
1
2
LOR
Liquid O-Ring
LOR
1Clamp screw

1-5
1
4st 4/5/6 2020
2) Instruments
For the following measuring instruments, use commercially available ones.
0XOWLPHWHU +,2.,6HULVH5HVLVWDQFHN$&YROWDJHWR9'&YROWDJH9
Vernier calipers ( M1 type, 300 mm )
Micrometer ( minimum graduation of 0.01, outer, 0 to 25 mm, 25 to 50 mm, 50 to 75 mm )
Cylinder gauge ( 4 to 6 mm, 10 to 25 mm, 25 to 50 mm, 50 to 75 mm )
Ring gauge ( ø5.5, ø16, ø30, ø59)
Dial gauge ( minimum graduation of 0.01 )
Thickness gauge ( 0.03 to 0.3 mm )
V block
Surface plate ( 500 mm x 500 mm )
Dial gauge magnet base or dial gauge stand
164 mm
9 mm
3. Tools and Instruments
1) Test Propeller
P/N. 3B2-64110-1
Outer diameter : 164mm
Width : 12mm
(Reference value)
This test propeller has been designed for break-in
operation and load test operation.
The engine speed at WOT varies depending on
the conditions such as the level or water of air
temperature, and this measurement is not the
confirmation of output.
Model
Speed at WOT
(Wide Open Throttle)
min-1 (rpm)
MFS 4D/5D 4,500 – 5,500
MFS 6D 5,000 – 6,000

1-6
Service Information
4st 4/5/6 2020
Inspecting pressure
Vacuum/Pressure Gauge
P/N. 3AC-99020-1
Removing spring pin
(ϕ3.0)
Spring Pin Tool A
P/N. 345-72227-0
Installing spring pin
(ϕ3.0)
Spring Pin Tool B
P/N. 345-72228-0
Removing spring pin
(ϕ3.5)
Spring Pin Tool A
P/N. 369-72217-0
Used in combination with driver rod and
bearing attachment to locate lower gear
case bearing
Center Plate
P/N. 3AB-99701-0
Used in combination with center plate and
bearing attachment
Driver Rod
P/N. 3AB-99702-0
Removing/installing flywheel
Flywheel Puller Kit
P/N. 369-72211-0
Removing or installing valve
springs
Valve Spring Compressor Attachment
P/N. 3AB-99076-0
Inspecting spark Installing piston Installing bearings
Bearing Attachment
P/N. 3BV-99905-0
Installing bearings
Needle Bearing Press Kit
P/N. 369-72900-0
3) Special Tools
Spark Tester
P/N. 3F3-72540-0
Piston Slider
P/N. 3H6-72871-0
Measuring engine revolution
speed
Tachometer
P/N. 3AC-99010-0
Measuring compression
pressure
Compression Gauge
P/N. 3AC-99030-0
Installing spring pin
(ϕ3.5)
Spring Pin Tool B
P/N. 369-72218-0
Measuring gaps
Thickness Gauge
P/N. 353-72251-1

1-7
1
4st 4/5/6 2020
Used to attach dial gauge
when measuring backlash
Dial Gauge Plate
P/N. 3B7-72729-0
Measuring gap between forward and
pinion gears (A and B gears)
Backlash Measuring Tool Kit
P/N. 369-72740-0
Measuring backlash
Clamp A
P/N. 3B7-72720-0

1-8
Service Information
4st 4/5/6 2020
ab
c
d
c
d
1
å∫
ç∂
1
2
3
4st OIL
4st
OIL
4. Pre-delivery Inspection
1) Steering Handle
åCheck installations for clattering and play.
∫Adjust steering friction.
çCheck throttle grip for movement. (Fully Open/Fully
Close).
∂Adjust throttle friction.
2) Gear Shift
1. Check that shift lever 1moves from neutral (N) to forward
(F)and reverse (R) smoothly.
(R)
N
(F)
1
F
R
N
21
4) Gear Oil
1. Check quantity of gear oil.
Gear Oil :
195 mL (6.6 fl.oz)
OIL
1Oil Level Gauge
1Oil Plug 2Gasket Do not reuse.
1Steering Adjust Screw cHeavier dLighter
3) Engine Oil
1. Set outboard motor upright.
2. Fill with Engine Oil.
4 Stroke Engine Oil :
450 mL (15.2 fl.oz)
OIL
CAUTION
Engine oil is removed before shipment to
prevent leakage during transportation.
3. Use oil level gauge 1to check oil quantity.
Fill with gear oil until some of the oil spills out of
the plug hole when the upper oil plug is removed.
2Upper limit 3Lower limit
When checking the oil level, screw in the oil level
gauge fully.

1-9
1
4st 4/5/6 2020
6) Rigging
1. Check that clamp bracket is fixed securely to hull.
2. Inspect boat bottom and atnti-ventilation plate to prevent the
engine from overheating or decreasing in propulsive force,
and, if necessary, adjust to prevent decrease in propulsive
force and engine overheating. a
1
[US]
7) Inspection of Tilt Stopper
1. Fully tilt up the outboard motor, lock with the tilt stopper 1,
and then check that the holding mechanism functions
normally.
1
Conduct a test run to determine the best
installation height. a5 - 25 mm (0.2 - 1.0 in)
Dual Tank model
1''FULL'' mark
Separate Tank model
5) Fuel Tank Line
1. Check that fuel tank contains sufficient amount of gasoline,
fuel line is connected and is free of leak.
CAUTION
Since this is a four stroke engine model, do
not use fuel mixed with engine oil. Use of
fuel mixed with engine oil will cause engine
trouble.
Anti-ventilation plate standard position a:
Anti-ventilation plate located 5 - 25 mm
(0.2 - 1.0 in) below boat bottom

1-10
Service Information
4st 4/5/6 2020
8) Inspection of Stop Switch
1. Press stop switch 1hard or pull out lock 2from stop switch
1to check that engine stops. 1
2
1
2
10) Idle Operation
1. After engine has warmed up in neutral, use tachometer to
check idle engine speed is as specified.
1
Idle Engine Speed :
1,300 min-1 (rpm)
RPM
9) Cooling Water Check Port
1. Check that cooling water check port 1discharges water
while the engine is running.
1
Tachometer :
P/N. 3AC-99010-0
1High Tension Cord
1Stop Switch 2Stop Switch Lock
1Stop Switch 2Stop Switch Lock