Yamaha MZ400 Manual

MZ400
MX400
SUPPLEMENTARY
SERVICE MANUAL
7HS-F8197-10LIT-19616-02-36
2016_02×1 !
7HS-F8197-10_cover.indd 1 2016/02/25 15:28:11

7HS-F8197-10_cover.indd 2 2016/02/25 15:28:11

FOREWORD
This Supplementary Service Manual has been
prepared to introduce service procedure and
data for the MZ400, MX400.
For complete information on service proce-
dures, it is necessary to use this Supplementary
Service Manual together with following manual:
This manual was written by the Yamaha Motor
Powered Products Co., Ltd. primarily for use
by Yamaha dealers and their qualified mechan-
ics. It is not possible to put an entire mechan-
ic’s education into one manual, so it is
assumed that persons using this book to per-
form maintenance and repairs on Yamaha
Multi-Purpose Engine have a basic under-
standing of the mechanical precepts and pro-
cedures inherent to Multi-Purpose Engine
repair technology. Without such knowledge,
attempted repairs or service to this model may
render it unfit for use and/or unsafe.
Yamaha Motor Powered Products Co., Ltd. is
continually striving to further improve all mod-
els manufactured by Yamaha. Modifications
and significant changes in specifications or
procedures will be forwarded to all Authorized
Yamaha dealers and will, where applicable,
appear in future editions of this manual.
TIP
This Service Manual contains information
regarding periodic maintenance to the
emission control system. Please read this
material carefully.
MX360
SERVICE MANUAL:
7HC-F8197-10/LIT-19616-02-32
MX360
SUPPLEMENTARY SERVICE MANUAL:
7HC-F8197-11/LIT-19616-02-34
MZ400, MX400
SUPPLEMENTARY SERVICE MANUAL
©2016 by Yamaha Motor
Corporation, U.S.A.
1st Edition, February 2016
All rights reserved. Any reprinting or
unauthorized use without the written
permission of Yamaha Motor
Corporation, U.S.A.
is expressly prohibited.
LIT-19616-02-36

HOW TO USE THIS MANUAL
PARTICULARLY IMPORTANT
INFORMATION
Particularly important information is distin-
guished in this manual by the following nota-
tions.
This is the safety alert symbol. It is used to
alert you to potential personal injury haz-
ards. Obey all safety messages that follow
this symbol to avoid possible injury or
death.
WARNING
A WARNING indicates a hazardous situa-
tion which, if not avoided, could result in
death or serious injury.
NOTICE
A NOTICE indicates special precautions
that must be taken to avoid damage to the
machine or other property.
TIP
A TIP provides key information to make proce-
dures easier or clearer.

HOW TO USE THIS MANUAL
This manual is intended as a handy, easy-to-read reference book for the mechanic.
Comprehensive explanations of all installation, removal, disassembly, assembly, repair and check
procedures are laid out with the individual steps in sequential order.
9The manual is divided into chapters and each chapter is divided into sections. The current sec-
tion title is shown at the top of each page 1.
9Sub-section titles appear in smaller print than the section title 2.
9To help identify parts and clarify procedure steps, there are exploded diagrams at the start of
each removal and disassembly section 3.
9Numbers are given in the order of the jobs in the exploded diagram. A number indicates a dis-
assembly step 4.
9Symbols indicate parts to be lubricated or replaced 5.
Refer to “ILLUSTRATED SYMBOLS”.
9A job instruction chart accompanies the exploded diagram, providing the order of jobs, names of
parts, notes in jobs, etc. 6. This step explains removal procedure only. For installation, reverse
the steps.
9Jobs requiring more information (such as special tools and technical data) are described
sequentially 7.
ENG
3-20
CYLINDER HEAD COVER, CYLINDER HEAD
6543
2
78
9
78
11 Nm (1.1 m · kgf, 8.0 ft · lbf)
20 Nm (2.0 m · kgf, 14 ft · lbf)
2.3 Nm (0.23 m · kgf, 1.7 ft · lbf)
12 Nm (1.2 m · kgf, 8.7 ft · lbf)
50 Nm (5.0 m · kgf, 36 ft · lbf)
1st
2nd
7 Nm (0.7 m · kgf, 5.1 ft · lbf)
9
1
Order Job/Parts to remove Q’ty Remarks
Removing the cylinder head cover,
cylinder head
Remove the parts in the order listed.
Fuel tank Refer to “FUEL TANK” on 3-4.
Muffler Refer to “MUFFLER” on 3-6.
Air filter Refer to “AIR FILTER” on 3-3.
Carburetor Refer to “CARBURETOR” on 4-1.
Flywheel cover Refer to “FLYWHEEL” on 3-12.
1 Spark plug cap 1
2 Spark plug 1
3 Air filter case stay 1
4 Cylinder head cover 1
5 Cylinder head cover gasket 1
6 Cylinder air shroud 1
7 Locknut 2
8 Adjuster 2
9 Screw 2
CYLINDER HEAD COVER, CYLINDER HEAD
ENG
3-22
CYLINDER HEAD COVER, CYLINDER HEAD
CHECKING THE PUSH ROD
1. Check:
9 Push rod runout
Runout limit:
Refer to “SPECIFICATIONS” in
the Supplementary service
manual.
Out of specifications → Replace.
CHECKING THE CYLINDER HEAD
1. Check:
9 Cylinder head combustion chamber
Check the combustion chamber for car-
bon deposits.
Any carbon deposits → Eliminate.
TIP
Be sure not to damage the contact surface of
the cylinder.
2. Check:
9 Cylinder head
Cracks/damage around the hole of
spark plug → Replace.
CHECKING THE ROCKER ARM
1. Check:
9 Rocker arm
Wear/damage/cracks → Replace.
1
4
3
6
7
2
5

ILLUSTRATED SYMBOLS
(Refer to the illustration)
SYMBOL DEFINITION SYMBOL DEFINITION
General information Periodic checks and
adjustments
Engine Carburetor
Electrical Troubleshooting
Specifications Filling fluid
Lubricant Special tool
T
R
.
.
Tightening torque Wear limit, clearance
Engine speed Electrical data
Replace the part with a new one. LS Lithium-soap base grease
MMolybdenum disulfide grease
E
Engine oil
M
Molybdenum disulfide oil LT Apply locking agent (LOCTITE®)

INDEX
GENERAL INFORMATION GEN
INFO
SPECIFICATIONS SPEC
1
2

CHAPTER 1.
GENERAL INFORMATION
MACHINE IDENTIFICATION .....................1-1
ENGINE SERIAL NUMBER..................1-1
STARTING SERIAL NUMBER..............1-1
CHAPTER 2.
SPECIFICATIONS
GENERAL SPECIFICATIONS ...................2-1
MAINTENANCE SPECIFICATIONS ..........2-3
ENGINE ................................................2-3
ELECTRICAL........................................2-7

1-1
GEN
INFO
MACHINE IDENTIFICATION
1
2
GENERAL INFORMATION
MACHINE IDENTIFICATION
ENGINE SERIAL NUMBER
The serial number is printed on the label 1
affixed to the position 2of the multi-purpose
engine as shown in the illustration.
TIP
The first four digits identify the model, and
the remaining digits indicates the production
number.
STARTING SERIAL NUMBER
Model Code Starting serial
number
MZ400KH2P6 7HSB 7HSB-1000101–
MX400AA6L6 7HSJ 7HSJ-1000101–
TIP
Designs and specifications are subject to
change without notice.
1

2-1
SPEC
GENERAL SPECIFICATIONS
SPECIFICATIONS
GENERAL SPECIFICATIONS
Model name: MZ400 MX400
Model code number: 7HSB 7HSJ
Dimensions:
Overall length mm (in) 456 (17.95) 392.5 (15.45)
(PTO:B type)
418 (16.46)
(PTO:A type)
Overall width mm (in) 479 (18.86) 462 (18.19)
(PTO:B type)
480 (18.90)
(PTO:A type)
Overall height mm (in) 306 (12.05) 490 (19.29)
(PTO:B type)
490 (19.29)
(PTO:A/B type)
Dry weight kg (lb) 33 (72.75) 33 (72.75)
(PTO:B type)
39 (85.98)
(PTO:A type)
Engine:
Engine type Air cooled 4-stroke gasoline OHV
Single cylinder
Cylinder arrangement
Displacement L (cm3)0.402 (402)
Bore × Stroke mm (in) 85.0 × 71.0 (3.35 × 2.80)
Compression ratio 8.2:1
Standard compression pressure
kPa (kg/cm2, psi) 450–550 (4.5–5.5, 65.3–79.8)
Net output* kW (PS) / r/min 8.93 (12.14) / 3600
Fuel Unleaded regular gasoline
Fuel tank capacity L (US gal, Imp gal) —6.1 (1.61, 1.34)
Engine oil quantity L (US qt, Imp qt) 1.1 (1.16, 0.97)
Recommended engine oil AYAMALUBE 4 (10W-40),
SAE 10W-30 or 10W-40
BSAE #30
CSAE #20
DSAE 10W
AYAMALUBE 4 (10W-40)
BSAE #30 CSAE #20 DSAE 10W
Recommended engine oil grade API Service SE type or higher
Lubrication system Forced splashing
Air filter system Dry
Cooling system Air cooled
Starting system Electric and
recoil starter
(PTO:K type)
Recoil starter (PTO:B type)
Electric and recoil starter
(PTO:A type)
Stopping system Misfire
Rotating direction Clockwise (from flywheel)
Governor type Centrifugal weight system

2-2
SPEC
GENERAL SPECIFICATIONS
Model name: MZ400 MX400
Model code number: 7HSB 7HSJ
Electrical:
Ignition system TCI
Ignition timing (3600 r/min) BTDC 23° ± 3°
Spark plug type BPR4ES (NGK)
Spark plug gap mm (in) 0.7–0.8 (0.028–0.031)
* The power rating of the engine indicated in the SPECIFICATIONS is the net power output tested
on an engine model and measured at 3600 r/min.
Actual power output for an installed engine will vary depending on numerous factors, including
the operating speed of the engine, environmental conditions, and other variables. 2

2-3
SPEC
MAINTENANCE SPECIFICATIONS
Model name: MZ400 MX400
Model code number: 7HSB 7HSJ
Piston: mm (in)
Piston clearance 0.015–0.029 (0.0006–0.0011)
<Limit> 0.06 (0.0024)
Piston skirt diameter “D” 84.977–84.998 (3.3455–3.3464)
<Limit> 84.921 (3.3433)
Measuring point “H” 10 (0.3937)
Oversize 1st 85.25 (3.3563)
2nd 85.5 (3.3661)
Piston pin hole inside diameter 20.004–20.015 (0.7876–0.7880)
<Limit> 20.045 (0.7892)
Piston pin: mm (in)
Piston pin diameter 19.995–20.000 (0.7872–0.7874)
<Limit> 19.975 (0.7864)
Piston ring: mm (in)
Top ring
Type Barrel
Dimensions “B × T” 1.2 × 3.1 (0.0472 × 0.1220)
End gap 0.20–0.35 (0.0079–0.0138)
<Limit> 0.6 (0.0236)
Side clearance 0.04–0.08 (0.0016–0.0031)
<Limit> 0.13 (0.0051)
2nd ring
Type Taper
Dimensions “B × T” 1.2 × 3.2 (0.0472 × 0.1260)
End gap 0.30–0.45 (0.0118–0.0177)
<Limit> 0.8 (0.0315)
Side clearance 0.03–0.07 (0.0012–0.0028)
<Limit> 0.13 (0.0051)
Oil ring
Type 3-piece type
Dimensions “B × T” 2.5 × 2.5 (0.0984 × 0.0984)
End gap 0.2–0.7 (0.0079–0.0276)
Cylinder head: mm (in)
Warpage limit 0.05 (0.002)
Cylinder: mm (in)
85.000–85.020 (3.3465–3.3472)
Inside diameter “D”
<Limit> 85.04 (3.348)
Taper limit 0.05 (0.002)
Warpage limit 0.05 (0.002)
MAINTENANCE SPECIFICATIONS
ENGINE
B
T

2-4
SPEC
MAINTENANCE SPECIFICATIONS
Model name: MZ400 MX400
Model code number: 7HSB 7HSJ
Crankshaft: mm (in)
Big end side clearance “A” 0.20–0.65 (0.008–0.026)
<Limit> 0.8 (0.0315)
Runout “B”
<Limit> 0.02 (0.0008)
Crank pin outside diameter “C” 35.969–35.984 (1.4161–1.4167)
<Limit> 35.90 (1.4134)
Crankshaft free play 0–0.2 (0.000–0.008)
Connecting rod: mm (in)
Small end diameter “A” 20.006–20.020 (0.7876–0.7882)
Oil clearance 0.006–0.025 (0.0002–0.0010)
Big end diameter “B” 36.000–36.015 (1.4173–1.4179)
Big end oil clearance 0.016–0.046 (0.0006–0.0018)
<Limit> 0.09 (0.0035)
Camshaft: mm (in)
Camshaft outside diameter 113.4–113.7 (4.465–4.476)
Camshaft lobe dimensions
“A” IN 32.5–32.6 (1.2795–1.2835)
<Limit> 32.3 (1.2717)
“A” EX 32.5–32.6 (1.2795–1.2835)
<Limit> 32.3 (1.2717)
“B” IN 26.0–26.1 (1.0236–1.0276)
<Limit> 25.8 (1.0157)
“B” EX 26.0–26.1 (1.0236–1.0276)
<Limit> 25.8 (1.0157)
Camshaft journal diameter 15.965–15.990 (0.6285–0.6295)
<Limit> 15.950 (0.628)

2-5
SPEC
MAINTENANCE SPECIFICATIONS
Model name: MZ400 MX400
Model code number: 7HSB 7HSJ
Valve: mm (in)
Head diameter “A” IN 31.9–32.1 (1.2559–1.2638)
EX 27.9–28.1 (1.0984–1.1063)
Stem diameter “B” IN 5.948–5.963 (0.2342–0.2348)
EX 5.940–5.955 (0.2339–0.2344)
<Limit> IN 5.918 (0.2330)
EX 5.910 (0.2327)
Stem length “C” IN 88.1 (3.4685)
EX 88.1 (3.4685)
Valve face contact width “D”
IN 0.7–0.9 (0.0276–0.0354)
EX 0.7–0.9 (0.0276–0.0354)
<Limit> IN 1.6 (0.063)
EX 1.6 (0.063)
Valve seat contact width IN 0.7–0.9 (0.0276–0.0354)
EX 0.7–0.9 (0.0276–0.0354)
<Limit> IN 1.6 (0.063)
EX 1.6 (0.063)
Valve seat width IN 0.7–0.9 (0.0276–0.0354)
EX 0.7–0.9 (0.0276–0.0354)
Valve margin thickness IN 1.0–1.4 (0.0394–0.0551)
EX 1.0–1.4 (0.0394–0.0551)
Valve stem runout limit 0.01 (0.0004)
“θ”90°
Valve guide
Guide inside diameter IN 6.000–6.012 (0.2362–0.2367)
EX 6.000–6.012 (0.2362–0.2367)
Stem to guide clearance IN 0.037–0.064 (0.0015–0.0025)
EX 0.045–0.072 (0.0018–0.0028)
Valve clearance (cold) IN 0.08–0.12 (0.0031–0.0047)
EX 0.08–0.12 (0.0031–0.0047)
Push rod: mm (in)
Runout limit 0.15 (0.0059)

2-6
SPEC
Model name: MZ400 MX400
Model code number: 7HSB 7HSJ
Valve spring: mm (in)
Free length IN 36.2 (1.4252)
EX 36.2 (1.4252)
<Limit> IN 34.39 (1.3539)
EX 34.39 (1.3539)
Installed length IN 29 (1.1417)
EX 29 (1.1417)
Installed compression spring force
IN N (kgf, lbf) 91.20–104.93 (9.12–10.49, 20.50–23.59)
EX N (kgf, lbf) 91.20–104.93 (9.12–10.49, 20.50–23.59)
Tilt limit mm (in) 1.7 (0.0669)
Carburetor: mm (in)
Type/manufacture RUIXNG
I.D. mark 7HP-E4301-**
Bore size ø26
Main jet 1.23 (0.050) 1.27 (0.050)
Main air jet 1.4 (0.055)
Pilot air jet 1.2 (0.045)
Pilot outlet 1.0 (0.039)
Valve seat size 1.8 (0.070)
Pilot jet 0.54 (0.02) 0.55 (0.02)
Pilot screw 1 3/4 turns out
Throttle valve 13° 14°
Float height “H” 14.9 (0.59)
Governor arm:
Tension spring attach hole
3 1
Engine speed: r/min
3700–3800 3750–3850
High engine speed
Low engine speed 1900–2100
1
2
3
4
5
6
7
8
9
MAINTENANCE SPECIFICATIONS

2-7
SPEC
MAINTENANCE SPECIFICATIONS
ELECTRICAL
Model name: MZ400 MX400
Model code number: 7HSB 7HSJ
Ignition system:
Ignition timing at 3600 r/min BTDC 23° ± 3°
Primary coil resistance (Ω± 20 %) 0.6
Secondary coil resistance (kΩ± 20 %) 11.2
Spark plug cap resistance kΩ3.75–6.25 (at 20 °C (68 °F))
TCI unit air gap mm (in) 0.4–0.6 (0.0157–0.0236)
Minimum spark gap mm (in) 6.0 (0.24)
Electric starting system:
Depth of insulator mm (in) 0.4–0.8 (0.0157–0.0315)
Insulation resistance MΩMore than 10
Brush spring pressure N (kgf, lbf) 13.1
Brush wear limit length mm (in) 6.0 (0.24)

7HS-F8197-10_cover.indd 2 2016/02/25 15:28:11

MZ400
MX400
SUPPLEMENTARY
SERVICE MANUAL
7HS-F8197-10LIT-19616-02-36
2016_02×1 !
7HS-F8197-10_cover.indd 1 2016/02/25 15:28:11