VMX12

SERVICE MANUAL

 1986 by Yamaha Motor Co., Ltd.

1st Edition, March 1986

All rights reserved. Any reprinting or

unauthorized use without the written

permission of Yamaha Motor Co., Ltd.

is expressly prohibited.

Printed in Japan

CAUTION:

WARNING:

NOTICE

This manual was written by the Yamaha Motor Company primarily for use by Yamaha dealers and their

qualified mechanics. It is not possible to put an entire mechanic’s education into one manual, so it is

assumed that persons using this book to perform maintenance and repairs on Yamaha motorcycles

have a basic understanding of the mechanical concepts and procedures inherent in motorcycle repair

technology. Without such knowledge, attempted repairs or service to this model may render it unfit to

use and/or unsafe.

Yamaha Motor Company, Ltd. is continually striving to improve all models manufactured by Yamaha.

Modifications and significant changes in specifications or procedures will be forwarded to all Autho-

rized Yamaha dealers and will, where applicable, appear in future editions of this manual.

TECHNICAL PUBLICATIONS

SERVICE DIVISION

MOTORCYCLES OPERATIONS

YAMAHA MOTOR CO., LTD.

HOW TO USE THIS MANUAL

PARTICULARLY IMPORTANT INFORMATION

This material is distinguished by the following notation.

NOTE:

A NOTE provides key information to make procedures easier or clearer.

A CAUTION indicates special procedures that must be followed to avoid damage

to the motorcycle.

A WARNING indicates special procedures that must be followed to avoid injury to

a motorcycle operator or person inspecting or repairing the motorcycle.

MANUAL FORMAT

All of the procedures in this manual are organized in a sequential, step-by-step format. The information

has been compiled to provide the mechanic with an easy to read, handy reference that contains com-

prehensive explanations of all disassembly, repair, assembly, and inspection operations.

In this revised format, the condition of a faulty component will precede an arrow symbol and the course

of action required will follow the symbol, e.g.,

Bearings

Pitting/Damage
Replace.

EXPLODED DIAGRAM

Each chapter provides exploded diagrams before each disassembly section for ease in identifying cor-

rect disassembly and assembly procedures.

19

1

3

5

7

9

2

4

8

6

21

20

18

16

17

15

13

14

10

12

11

INSP

ADJ

GEN

INFO

ENG

CARB

ELEC

CHAS

COOL

APPX

ILLUSTRATED SYMBOLS

(Refer to the illustration)

Illustrated symbols 1 to 8 are designed as

thumb tabs to indicate the chapter’s number

and content.

1 General information

2 Periodic inspection and adjustment

3 Engine

4 Cooling system

5 Carburetion

6 Chassis

7 Electrical

8 Appendices

Illustrated symbols 9 to ¹⁴ are used to identify

the specifications appearing in the text.

9 Filling fluid

10 Lubricant

11 Tightening

12 Wear limit, clearance

13 Engine speed

14 Ω, V, A

Illustrated symbols ¹⁵ to ²¹ in the exploded dia-

gram indicate grade of lubricant and location of

lubrication point.

15 Apply engine oil

16 Apply gear oil

17 Apply molybdenum disulfide oil

18 Apply wheel bearing grease

19 Apply lightweight lithium-soap base grease

20 Apply molybdenum disulfide grease

21 Apply locking agent (LOCTITE^)

GENERAL INFORMATION

PERIODIC INSPECTIONS

AND ADJUSTMENTS

ENGINE OVERHAUL

COOLING SYSTEM

CARBURETION

CHASSIS

ELECTRICAL

APPENDICES

GEN

INFO 1

2

3

ENG

4

5

CARB

6

CHAS

7

ELEC

8

INSP

ADJ

COOL

APPX

INDEX

GEN

INFO

CHAPTER 1.

GENERAL INFORMATION

MOTORCYCLE IDENTIFICATION

1-1

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

FRAME SERIAL NUMBER

1-1

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

ENGINE SERIAL NUMBER

1-1

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

IMPORTANT INFORMATION

1-2

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

ALL REPLACEMENT PARTS

1-2

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

GASKETS, OIL SEALS, AND O-RINGS

1-2

. . . . . . . . . . . . . . . . . . . . . . . .

LOCK WASHERS/PLATES AND COTTER PINS

1-2

. . . . . . . . . . . . . . . .

BEARINGS AND OIL SEALS

1-2

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

CIRCLIPS

1-3

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

SPECIAL TOOLS

1-3

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

FOR TUNE-UP

1-3

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

FOR ENGINE SERVICE

1-4

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

FOR CHASSIS SERVICE

1-8

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

FOR MIDDLE GEAR SERVICE

1-9

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

FOR ELECTRICAL COMPONENTS

1-10

. . . . . . . . . . . . . . . . . . . . . . . . . . .

GEN

INFO

1-1

MOTORCYCLE IDENTIFICATION

GEN

INFO

NOTE:

NOTE:

GENERAL INFORMATION

MOTORCYCLE IDENTIFICATION

FRAME SERIAL NUMBER

The frame serial number 1 is stamped into the

steering head pipe.

ENGINE SERIAL NUMBER

The engine serial number 1 is stamped into the

left side of the engine.

The first three digits of these numbers are for

model identifications; the remaining digits are

the unit production number.

Starting Serial Number:

VMX12

2EN-000101

. . . . . . . . . . .

Designs and specifications are subject to

change without notice.

1-2

IMPORTANT INFORMATION

GEN

INFO

CAUTION:

IMPORTANT INFORMATION

ALL REPLACEMENT PARTS

1. We recommend to use Yamaha genuine

parts for all replacements. Use oil and/or

grease recommended by Yamaha for as-

sembly and adjustment.

GASKETS, OIL SEALS, AND O-RINGS

1. All gaskets, seals, and O-rings should be re-

placed when an engine is overhauled. All

gasket surfaces, oil seal lips, and O-rings

must be cleaned.

2. Properly oil all mating parts and bearings

during reassembly. Apply grease to the oil

seal lips.

LOCK WASHERS/PLATES AND COTTER

PINS

1. All lock washers/plates 1 and cotter pins

must be replaced when they are removed.

Lock tab(s) should be bent along the bolt or

nut flat(s) after the bolt or nut has been prop-

erly tightened.

BEARINGS AND OIL SEALS

1. Install the bearing(s) 1 and oil seal(s) 2

with their manufacturer’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 coat-

ing of light-weight lithium base grease to the

seal lip(s). Oil the bearings liberally when

installing.

Do not use compressed air to spin the bear-

ings dry. This causes damage to the bearing

surfaces.

1-3

SPECIAL TOOLS

GEN

INFO

CIRCLIPS

1. All circlips should be inspected carefully be-

fore reassembly. Always replace piston pin

clips after one use. Replace distorted cir-

clips. When installing a circlip 1 , make sure

that the sharp-edged corner 2 is positioned

opposite to the thrust 3 it receives. See the

sectional view.

4 Shaft

SPECIAL TOOLS

The proper special tools are necessary for com-

plete and accurate tune-up and assembly. Us-

ing the correct special tool will help prevent

damage caused by the use of improper tools or

improvised techniques.

FOR TUNE UP

1. Inductive Tachometer

P/N 90890-03113

This tool is needed for detecting engine rpm.

2. Inductive Timing Light

P/N 90890-03109

This tool is necessary for checking ignition tim-

ing.

3. Compression Gauge

P/N 90890-03081

This gauge is used to measure the engine com-

pression.

1-4

SPECIAL TOOLS

GEN

INFO

4. Fuel Level Gauge

P/N 90890-01312

This gauge is used to measure the fuel level in

the float chamber.

5. Vacuum Gauge

P/N 90890-03094

This gauge is needed for carburetor synchro-

nization.

6. Radiator Cap Tester

P/N 90890-01325

This tester is needed for checking the cooling

system.

FOR ENGINE SERVICE

1. Clutch Holder

P/N 90890-04086

This tool is used to hold the clutch when remov-

ing or installing the clutch boss locknut.

2. Tappet Adjusting Tool

P/N 90890-04105

This tool is necessary to replace valve adjusting

pads.

1-5

SPECIAL TOOLS

GEN

INFO

3. Valve Spring Compressor

P/N 90890-04019

This tool is needed to remove and install the

valve assemblies.

4. Valve Guide Remover (5.5 mm)

P/N 90890-01122

This tool is used to remove the valve guides.

5. Valve Guide Reamer (5.5 mm)

P/N 90890-01196

This tool is used to rebore the new valve guide.

6. Valve Guide Installer

P/N 90890-04015

This tool is needed to install the valve guides

properly.

7. Valve Seat Cutter Set

P/N YM-91043

This tool is needed to resurface the valve seat.

1-6

SPECIAL TOOLS

GEN

INFO

8. Flywheel Puller

P/N 90890-01362 – 1

Adapter

P/N 90890-04089 – 2

These tools are used to remove the flywheel.

9. 8 mm Wrench Adapter

P/N 90890-04076

This tool is used to loosen or tighten the cylinder

head securing nut.

10. Piston Ring Compressor

P/N 90890-05158

This tool is used when installing the piston into

the cylinder.

11. Water Pump Seal Installer

Handle

P/N 90890-04058 – 1

Adapter

P/N 90890-04078 – 2

This tool is needed for proper installation of the

water pump seal.

12. Piston Pin Puller

P/N 90890-01304

This tool is used to remove the piston pin.

1-7

SPECIAL TOOLS

GEN

INFO

13. #40 Torx Driver

P/N 90890-04049

This tool is used to loosen or tighten the middle

gear bearing retainer bolt.

14. #30 Torx Driver

P/N YU-29843-6

This tool is used to loosen or tighten the drive

axle bearing retainer bolt.

15. #25 Torx Driver

P/N YU-29843-4

This tool is used to loosen or tighten the shift

cam segment securing bolt.

16. Plastigage Set “Green”

P/N YU-33210

This gauge is needed to measure the clearance

for the connecting rod bearing.

17. Special Torx Driver

P/N 90890-05349

This tool is used when overhauling the carbure-

tors.