Yamaha MX800V User manual

SERVICE MANUAL
MX800V
MX825V
7UC-F8197-E0LIT-19616-02-50
2017.10×1 !
7UC-F8197-E0_Hyoshi.indd 1-2 2017/10/27 13:08:23

7UC-F8197-E0_Hyoshi.indd 3-4 2017/10/27 13:08:23

MX800V, MX825V
SERVICE MANUAL
©2017 by Yamaha Motor
Corporation, U.S.A.
1st Edition, October 2017
All rights reserved. Any reprinting or
unauthorized use without the written
permission of Yamaha Motor
Corporation, U.S.A.
is expressly prohibited.
LIT-19616-02-50

IMPORTANT
This manual was produced by the Yamaha Motor Powered Products Co., Ltd. primarily for use by
Yamaha dealers and their qualified mechanics. It is not possible to include all the knowledge of a
mechanic in one manual. Therefore, anyone who uses this book to perform maintenance and
repairs on Yamaha machines should have a basic understanding of mechanics and the techniques
to repair these types of machines. Repair and maintenance work attempted by anyone without this
knowledge is likely to render the machine unsafe and unfit for use.
This model has been designed and manufactured to perform within certain specifications in regard
to performance and emissions. Proper service with the correct tools is necessary to ensure that the
machine will operate as designed. If there is any question about a service procedure, it is imperative
that you contact a Yamaha dealer for any service information changes that apply to this model. This
policy is intended to provide the customer with the most satisfaction from their machine and to con-
form to federal environmental quality objectives.
Yamaha Motor Powered Products Co., Ltd. is continually striving to improve all of its models. Modifi-
cations and significant changes in specifications or procedures will be forwarded to all authorized
Yamaha dealers and will appear in future editions of this manual where applicable.
TIP
• This Service Manual contains information regarding periodic maintenance to the emission control
system. Please read this material carefully.
• Designs and specifications are subject to change without notice.
IMPORTANT MANUAL INFORMATION
Particularly important information is distinguished in this manual by the following notations.
This is the safety alert symbol. It is used to alert you to potential personal injury hazards.
Obey all safety messages that follow this symbol to avoid possible injury or death.
A WARNING indicates a hazardous situation which, if not avoided, could result in death or
serious injury.
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 procedures easier or clearer.
WARNING
NOTICE

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.
• The manual is divided into chapters and each chapter is divided into sections. The current section
title is shown at the top of each page “1”.
• Sub-section titles appear in smaller print than the section title “2”.
• To help identify parts and clarify procedure steps, there are exploded diagrams at the start of each
removal and disassembly section “3”.
• Numbers are given in the order of the jobs in the exploded diagram. A number indicates a disas-
sembly step “4”.
• Symbols indicate parts to be lubricated or replaced “5”.
Refer to “SYMBOLS”.
• A 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.
• Jobs requiring more information (such as special tools and technical data) are described sequen-
tially “7”.
1
3
7
2
4
5
6

SYMBOLS
The following symbols are used in this manual for easier understanding.
TIP
The following symbols are not relevant to every machine.
SYMBOL DEFINITION SYMBOL DEFINITION
Filling fluid Lubricant
Special tool Tightening torque
Wear limit, clearance Engine speed
Electrical data Replace the part with a new one.
Lithium-soap base grease Molybdenum disulfide grease
Engine oil Silicone fluid
Apply locking agent (LOCTITE®)
T
R
.
.
New
LS
M
E
S
LT

GENERAL INFORMATION
PERIODIC CHECKS AND
ADJUSTMENTS
ENGINE
FUEL
ELECTRICAL
TROUBLESHOOTING
SPECIFICATIONS
1
2
3
4
5
6
7
8
9
10
INDEX

TABLE OF CONTENTS
GENERAL INFORMATION
MACHINE IDENTIFICATION ......................1-1
SERIAL NUMBER .................................1-1
STARTING SERIAL NUMBER...............1-1
DIMENSIONS .............................................1-2
TOP .......................................................1-2
MOUNTING BASE ................................1-2
REAR.....................................................1-3
REAR (For models equipped with a
muffler) ..................................................1-3
RIGHT SIDE ..........................................1-4
RIGHT SIDE (For models equipped
with a muffler) ........................................1-4
IMPORTANT INFORMATION .....................1-5
PREPARATION FOR REMOVAL AND
DISASSEMBLY......................................1-5
CAUTION ON SERVICE........................1-5
NOTES ON SERVICE ...........................1-5
ALL REPLACEMENT PARTS................1-6
GASKETS, OIL SEALS, AND
O-RINGS ...............................................1-6
BEARINGS AND OIL SEALS ................1-7
BASIC SERVICE INFORMATION ..............1-7
ELECTRICAL SYSTEM.........................1-7
SPECIAL TOOLS AND TESTERS ...........1-10
PERIODIC CHECKS AND
ADJUSTMENTS
INTRODUCTION.........................................2-1
MAINTENANCE INTERVALS CHART .......2-1
PERIODIC MAINTENANCE/
LUBRICATION INTERVALS.......................2-1
PERIODIC MAINTENANCE .......................2-2
SPARK PLUGS......................................2-2
MUFFLER
(For models equipped with a muffler) ....2-3
ENGINE OIL LEAKAGE ........................2-4
ENGINE OIL LEVEL..............................2-5
REPLACING THE ENGINE OIL ............2-6
FUEL LEAKAGE....................................2-8
FUEL FILTER ........................................2-8
OIL COOLER ........................................ 2-9
AIR FILTER ELEMENT ......................... 2-9
ADJUSTING THE VALVE
CLEARANCE ........................................ 2-9
CYLINDER HEADS
DECARBONIZATION .......................... 2-13
ENGINE SPEED ................................. 2-14
ADJUSTING THE ENGINE SPEED.... 2-15
LOW ENGINE SPEED (Replace the
carburetor assembly) .......................... 2-16
FITTINGS AND FASTENERS............. 2-17
ENGINE
ENGINE INSPECTION............................... 3-1
MEASURING THE COMPRESSION
PRESSURE .......................................... 3-1
AIR FILTER ................................................ 3-3
MUFFLER (For models equipped with a
muffler) ...................................................... 3-4
OIL COOLER ............................................. 3-5
REMOVING THE OIL COOLER............ 3-6
CHECKING THE OIL COOLER ............ 3-6
INSTALLING THE OIL COOLER .......... 3-6
RECTIFIER/REGULATOR ......................... 3-8
CASE AND FAN......................................... 3-9
REMOVING THE CASE AND FAN ..... 3-10
CHECKING THE CASE AND FAN...... 3-11
INSTALLING THE CASE AND FAN .... 3-11
TCI UNITS, FLYWHEEL AND STATOR
COIL ASSEMBLY..................................... 3-13
TCI UNITS........................................... 3-13
FLYWHEEL AND STATOR COIL
ASSEMBLY ......................................... 3-14
REMOVING THE FLYWHEEL AND
STATOR COIL ASSEMBLY ................. 3-15
CHECKING THE FLYWHEEL AND
STATOR COIL ASSEMBLY ................. 3-16
INSTALLING THE FLYWHEEL AND
STATOR COIL ASSEMBLY ................. 3-16
INSTALLING THE TCI UNITS............. 3-18
CYLINDER HEAD COVERS, CYLINDER
HEADS ..................................................... 3-19
CYLINDER HEAD #1.......................... 3-19

CYLINDER HEAD #2 ..........................3-21
CHECKING THE ROCKER ARMS
AND ROCKER ARM SHAFTS.............3-23
CHECKING THE PUSH RODS ...........3-23
REMOVING THE CYLINDER
HEADS ................................................3-23
CHECKING THE CYLINDER
HEADS ................................................3-23
INSTALLING THE CYLINDER HEAD
ASSEMBLY..........................................3-24
VALVES ....................................................3-26
REMOVING THE VALVES AND
VALVE SPRINGS.................................3-27
CHECKING THE VALVES AND
VALVE SPRINGS.................................3-27
CHECKING THE VALVE SEATS .........3-29
VALVE LAPPING .................................3-30
INSTALLING THE VALVES AND
VALVE SPRINGS.................................3-31
OIL PUMP.................................................3-32
DISASSEMBLING THE OIL PUMP.....3-33
CHECKING THE OIL PUMP ...............3-33
CHECKING THE RELIEF VALVE ........3-34
CHECKING THE CRANKCASE
COVER 2 .............................................3-34
INSTALLING THE OIL PRESSURE
SWITCH ..............................................3-34
ASSEMBLING THE OIL PUMP...........3-35
INSTALLING THE CRANKCASE
COVER 2 .............................................3-36
PISTONS, CAMSHAFT, CRANKCASE,
AND CRANKSHAFT ................................3-37
CRANKCASE ......................................3-37
PISTONS, CAMSHAFT, AND
CRANKSHAFT ....................................3-39
REMOVING THE FLYWEIGHT
SHAFT ASSEMBLY AND
GOVERNOR FORK.............................3-40
DISASSEMBLING THE FLYWEIGHT
SHAFT ASSEMBLY ............................. 3-40
CHECKING THE FLYWEIGHT
SHAFT ASSEMBLY ............................. 3-40
ASSEMBLING THE FLYWEIGHT
SHAFT ASSEMBLY ............................. 3-41
INSTALLING THE FLYWEIGHT
SHAFT ASSEMBLY AND
GOVERNOR FORK.............................3-41
REMOVING THE CAMSHAFT AND
VALVE LIFTERS ................................. 3-42
CHECKING THE CAMSHAFT ............ 3-42
CHECKING THE VALVE LIFTERS ..... 3-43
CHECKING THE REED VALVE .......... 3-44
INSTALLING THE VALVE LIFTERS
AND CAMSHAFT................................ 3-44
INSTALLING THE COVER 1............... 3-44
INSTALLING THE COVER 2............... 3-45
CHECKING THE CRANKCASE
COVER 1 ............................................ 3-45
INSTALLING THE CRANKCASE
COVER 1 ............................................ 3-46
CHECKING THE CYLINDERS AND
PISTONS ............................................ 3-46
CHECKING THE CRANKCASE.......... 3-48
CHECKING THE PISTON PINS ......... 3-48
CHECKING THE PISTON RINGS ...... 3-48
CHECKING THE CRANKSHAFT........ 3-50
CHECKING THE CONNECTING
RODS OIL CLEARANCE .................... 3-51
INSTALLING THE PISTONS AND
PISTON RINGS .................................. 3-52
INSTALLING THE CRANKSHAFT ...... 3-53
FUEL
FUEL PUMP............................................... 4-1
CHECKING THE FUEL PUMP ............. 4-2
CARBURETOR ASSEMBLY...................... 4-3
REMOVING THE CARBURETOR......... 4-3
DISASSEMBLING THE
CARBURETOR ..................................... 4-4
REMOVING THE CARBURETOR
ASSEMBLY ........................................... 4-5
CHECKING THE CARBURETOR
ASSEMBLY ........................................... 4-5
INSTALLING THE CARBURETOR
ASSEMBLY ........................................... 4-5
INTAKE MANIFOLD................................... 4-7
REMOVING THE INTAKE
MANIFOLD............................................ 4-8
CHECKING THE INTAKE
MANIFOLD............................................ 4-8
INSTALLING THE INTAKE
MANIFOLD............................................ 4-8

ELECTRICAL
CIRCUIT DIAGRAM....................................5-1
ELECTRICAL COMPONENTS...................5-3
CHECKING THE SWITCH
CONTINUITY.........................................5-5
CHECKING THE OIL PRESSURE
SWITCH ................................................5-5
CHECKING THE TCI UNIT
RESISTANCE ........................................5-5
CHECKING THE IGNITION SPARK
GAP .......................................................5-6
CHECKING THE SPARK PLUG
CAPS.....................................................5-7
CHECKING THE STATOR COIL
ASSEMBLY............................................5-7
CHECKING THE RECTIFIER/
REGULATOR.........................................5-8
CHECKING THE STARTER MOTOR
OPERATION ..........................................5-8
ELECTRIC STARTING SYSTEM .............5-10
REMOVING THE STARTER
MOTOR................................................5-10
DISASSEMBLING THE STARTER
MOTOR................................................5-11
CHECKING THE ARMATURE COIL ...5-12
CHECKING THE BRUSH ....................5-13
CHECKING THE STARTER RELAY....5-13
ASSEMBLING THE STARTER
MOTOR................................................5-13
TROUBLESHOOTING
ENGINE DOES NOT START ......................6-1
IGNITION SYSTEM...............................6-1
ELECTRIC STARTING SYSTEM .........6-2
OTHER TROUBLES ...................................6-3
ENGINE STARTS BUT STALLS ............6-3
ENGINE SPEED DOES NOT
INCREASE ............................................6-4
ENGINE SPEED IS UNEVEN ...............6-5
THE BATTERY IS NOT CHARGED.......6-6
GOVERNOR OPERATION ....................6-7
OIL PRESSURE SYSTEM..........................6-8
SPECIFICATIONS
GENERAL SPECIFICATIONS ................... 7-1
MAINTENANCE SPECIFICATIONS .......... 7-3
ENGINE ................................................ 7-3
ELECTRICAL........................................ 7-7
TIGHTENING TORQUES........................... 7-8
GENERAL TORQUE
SPECIFICATIONS.................................... 7-10
LUBRICATION POINTS AND TYPE OF
LUBRICANTS .......................................... 7-11
WIRE ROUTING DIAGRAM..................... 7-12
UPPER SIDE VIEW ............................ 7-12
LEFT SIDE VIEW................................ 7-16
RIGHT SIDE VIEW ............................. 7-18
REAR SIDE VIEW............................... 7-24

1
2
3
4
5
6
7
8
9
10
GENERAL INFORMATION
1-1
GENERAL INFORMATION
MACHINE IDENTIFICATION
SERIAL NUMBER
The serial number is printed on the label “1” affixed to the
position of the multi-purpose engine as shown in the illus-
tration.
TIP
• The first four digits identify the model, and the remaining
digits indicates the production number.
• Designs and specifications are subject to change without
notice.
STARTING SERIAL NUMBER
:
1
Model Code Starting serial num-
ber
MX800VH7J6 7U3J00 7U3J-1000101–
MX825VH7J6 7UCJ00 7UCJ-1000101–

DIMENSIONS
1-2
1
2
3
4
5
6
7
8
9
10
GENERAL INFORMATION
DIMENSIONS
TOP
MOUNTING BASE
*1: UNC: Unified coarse thread (Unit: in)
*2: PCD: Pitch Circle Diameter
mm (in)
mm (in)
499.2(19.65)
157.1(6.19)
35°
35°
45°
45°
PCD 254
4 3/8-16UNC

1-3
1
2
3
4
5
6
7
8
9
10
GENERAL INFORMATION
DIMENSIONS
REAR
REAR (For models equipped with a muffler)
mm (in)
mm (in)
451.2(17.76)
235.1(9.26)
451.2(17.76)
445.4(17.54)
235.1(9.26)

DIMENSIONS
1-4
1
2
3
4
5
6
7
8
9
10
GENERAL INFORMATION
RIGHT SIDE
RIGHT SIDE (For models equipped with a muffler)
mm (in)
mm (in)
416.2(16.39)
108.8(4.28) 639(25.16)
416.2(16.39)
116.7(4.59) 108.8(4.28)
639(25.16)

1-5
1
2
3
4
5
6
7
8
9
10
GENERAL INFORMATION
IMPORTANT INFORMATION
IMPORTANT INFORMATION
PREPARATION FOR REMOVAL AND
DISASSEMBLY
CAUTION ON SERVICE
Fire prevention
When servicing the engine, always keep the engine and
yourself away from fire.
NOTES ON SERVICE
Correct tools
Be sure to use the correct special tool for the job to guard
against damage.
Oil, grease and seals
Be sure to use genuine Yamaha oils, grease and sealers,
or the equivalents.
Expendable parts
Always replace the gaskets, O-rings, cotter pins and cir-
clips with new parts when servicing engine.

IMPORTANT INFORMATION
1-6
1
2
3
4
5
6
7
8
9
10
GENERAL INFORMATION
Tightening torque
Be sure to follow torque specifications. When tightening
bolts, nuts or screws, start with the largest-diameter fas-
tener and work from an inner position to an outer position
in a crisscross pattern.
Notes on disassembly and assembly
• Parts should be cleaned in solvent and blown dry with
compressed air after disassembly.
• Contact surfaces of moving parts should be oiled when
reassembled.
• Make sure that the parts, move smoothly after each sec-
tion of the machine is assembled.
ALL REPLACEMENT PARTS
We recommend the use of genuine Yamaha parts for all
replacements. Use oil and/or grease, recommended by
Yamaha, for assembly and adjustment.
GASKETS, OIL SEALS, AND O-RINGS
1. All gaskets, seals, and O-rings should be replaced
when an engine is overhauled. All gaskets surfaces,
oil seal lips, and O-rings must be cleaned.
2. Properly oil all mating parts and bearings during reas-
sembly. Apply grease to the oil seal lips.

1-7
1
2
3
4
5
6
7
8
9
10
GENERAL INFORMATION
BASIC SERVICE INFORMATION
BEARINGS AND OIL SEALS
Install the bearing(s) “1” and oil seal(s) “2” with their manu-
facture’s marks or numbers facing outward. (In other
words, the stamped letters must be on the side exposed to
view.) When installing oil seal(s), apply a light coating of
lightweight lithium base grease to the seal lip(s). Oil the
bearings liberally when installing.
BASIC SERVICE INFORMATION
ELECTRICAL SYSTEM
Checking the electrical system
TIP
Before checking the electrical system, make sure that the
battery voltage is at least 12 V.
1
2
Do not use compressed air to spin the bearings dry.
This causes damage to the bearing surfaces.
NOTICE
a
Never insert the tester probes into the coupler termi-
nal slots. Always insert the probes from the opposite
end “a” of the coupler, taking care not to loosen or
damage the leads.
NOTICE

BASIC SERVICE INFORMATION
1-8
1
2
3
4
5
6
7
8
9
10
GENERAL INFORMATION
Checking the connections
Check the leads, couplers, and connectors for stains, rust,
moisture, etc.
1. Disconnect:
• Lead
• Coupler
• Connector
2. Check:
• Lead
• Coupler
• Connector
Moisture Dry with an air blower.
Rust/stains Connect and disconnect several
times.
• When disconnecting a coupler, release the coupler
lock, hold both sections of the coupler securely, and
then disconnect the coupler.
• There are many types of coupler locks; therefore, be
sure to check the type of coupler lock before discon-
necting the coupler.
NOTICE
When disconnecting a connector, do not pull the
leads. Hold both sections of the connector securely,
and then disconnect the connector.
NOTICE

1-9
1
2
3
4
5
6
7
8
9
10
GENERAL INFORMATION
BASIC SERVICE INFORMATION
3. Connect:
• Lead
• Coupler
• Connector
TIP
• When connecting a coupler or connector, push both sec-
tions of the coupler or connector together until they are
connected securely.
• Make sure all connections are tight.
4. Check:
• Continuity
(with the digital circuit tester)
TIP
• If there is no continuity, clean the terminals.
• When checking the wire harness, perform steps (1) to
(3).
• As a quick remedy, use a contact revitalizer available at
most part stores.
Model 88 Multimeter with tachometer:
YU-A1927
For waterproof couplers, never insert the tester leads
directly into the coupler. When performing any checks
using a waterproof coupler, use the specified test har-
ness or a suitable commercially available test harness.
NOTICE

SPECIAL TOOLS AND TESTERS
1-10
1
2
3
4
5
6
7
8
9
10
GENERAL INFORMATION
SPECIAL TOOLS AND TESTERS
The proper special tools are necessary for complete and accurate tune-up and assembly. Using the
correct special tool will help prevent damage caused by the use of improper tools or improvised
techniques.
Valve spring compressor
90890-01253
Ignition checker
90890-06754
Digital tachometer
YU-39951-B, 90890-
06760
Feeler gauge set
YU-26900-9
Oil filter wrench
YM-01469
Engine compression tes-
ter
YU-33223
Primary clutch holder
YU-01235
Rotor holding tool
90890-01235
Heavy duty puller
YU-33270-B
Cylinder gauge
Commercially obtainable
Piston ring compressor
YM-08037
Dial indicator gauge
YU-A8428
Pressure/vacuum tester
YB-35956-B
Model 88 Multimeter with
tachometer
YU-A1927
66.8
YU-33223
SVU1160