Yamaha SR125 1997 User manual

EB000000
SR125
SERVICE MANUAL
1996 by Yamaha Motor Co., Ltd.
1st Edition, September 1996
All rights reserved. Any reprinting or
unauthorized use without the written
permission of Yamaha Motor Co., Ltd.
is expressly prohibited.

NOTE:
WARNING
CAUTION:
EB001000 NOTICE
This manual was produced by the Yamaha Motor Company primarily for use byYamaha dealers and
their qualified mechanics. It is not possible to include all the knowledge of a mechanic in one manual,
so it is assumed that anyone who uses this book to perform maintenance and repairs on Yamaha mo-
torcycle has a basic understanding of the mechanical ideas and the procedures of motorcycle repair.
Repairs attempted by anyone without this knowledge are likely to render the motorcycle unsafe and
unfit for use.
YamahaMotorCompany,Ltd.,iscontinuallystrivingtoimproveallitsmodels.Modificationsandsignif-
icant changes in specifications or procedures will be forwarded to all authorized Yamaha dealers and
will appear in future aditions of this manual where applicable.
Designs and specifications are subject to change without notice.
IMPORTANT INFORMATION
Particularly important information is distinguished in this manual by the following notations.
The Safety Alert Symbol means ATTENTION! BECOME ALERT!
YOUR SAFETY IS INVOLVED!
FailuretofollowWARNINGinstructionscouldresultin severe injuryor
deathtothemotorcycleoperator,abystanderorapersoninspectingor
repairing the motorcycle.
A CAUTION indicates special precautions that must be taken to avoid
damage to the motorcycle.
NOTE: A NOTE provides key information to make procedures easier or clearer.

1
2
6
7
6
43
8
YP002000 HOW TO USE THIS MANUAL
MANUAL ORGANIZATION
This manual consists of chapters for the main categories of subjects. (See “Illustrated symbols”)
1st title 1: This is the title of the chapter with its symbol on the upper right corner of each page.
2nd title 2: This title indicates the section of the chapter and only appears on the first page of each
section. It is located in the upper left corner of the page.
3rd title 3: This title indicates a sub-section that is followed by step-by-step procedures accompa-
nied by corresponding illustrations.
EXPLODED DIAGRAMS
Tohelpidentifypartsandclarifyproceduresteps,thereareexplodeddiagramsatstartofeachremoval
and disassembly section.
1. An easy-to-see exploded diagram 4is provided for disassembly and assembly jobs.
2. Numbers 5are given in the order of jobs in the exploded diagram. A number that is enclosed by a
circle indicates a disassembly step.
3. An explanation of jobs and notes is presented in an easy-to-read way by the use of symbol marks
6. The meanings of the symbol marks are given on the next page.
4. Ajobinstructionchart 7accompaniestheexplodeddiagram, providingtheorderofjobs, namesof
parts, notes in jobs, etc.
5. Forjobsrequiringmoreinformation,thestep-by-stepformatsupplements 8aregiveninadditionto
the exploded diagram and the job instruction chart.

21
1
3
5
7
9
2
4
8
6
23 24
2220
18 1917
15
1413
11 12
10
GEN
INFO SPEC
ENG
CARB
ELEC
CHAS
INSP
ADJ
TRBL
SHTG
16
EB003000
ILLUSTRATED SYMBOLS
Illustrated symbols 1to 9are designed as
thumb tabs to indicate the chapter’s number
and content.
1General information
2Specifications
3Periodic inspection and adjustment
4Engine
5Carburation
6Chassis
7Electrical
8Troubleshooting
Illustrated symbols 9to 16 are used to identify
the specifications appearing in the text.
9Possible to maintain with engine mounted
10 Filling fluid
11 Lubricant
12 Special tool
13 Tightening
14 Wear limit, clearance
15 Engine speed
16 Ω, V, A
Illustratedsymbols 17 to 22 in theexploded dia-
grams indicate the types of lubricants and lu-
brication points.
17 Apply engine oil
18 Apply gear oil
19 Apply molybodenum disulfide oil
20 Apply wheel bearing grease
21 Apply lightweight lithium-soap baes grease
22 Apply molybdenum disulfide grease
Illustratedsymbols 23 to 24 in theexploded dia-
gramsindicatethewheretoapplylockingagent
23 and when to install new parts 24 .
23 Apply locking agent (LOCTITE)
24 Use new one

GENERAL INFORMATION
SPECIFICATIONS
PERIODIC INSPECTION AND
ADJUSTMENT
ENGINE OVERHAUL
CARBURATION
CHASSIS
ELECTRICAL
TROUBLESHOOTING
GEN
INFO 1
SPEC 2
3
ENG 4
CARB 5
CHAS 6
ELEC 7
TRBL
SHTG 8
INSP
ADJ
INDEX

CHAPTER 1.
GENERAL INFORMATION
MOTORCYCLE IDENTIFICATION 1-1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
FRAME SERIAL NUMBER 1-1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
ENGINE SERIAL NUMBER 1-1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
MODEL LABEL 1-1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
IMPORTANT INFORMATION 1-2. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
PREPARATION FOR REMOVAL PROCEDURES 1-2. . . . . . . . . . . . . . .
REPLACEMENT PARTS 1-2. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
GASKETS, OIL SEALS AND O-RINGS 1-2. . . . . . . . . . . . . . . . . . . . . . . .
LOCK WASHERS/PLATES AND COTTER PINS 1-3. . . . . . . . . . . . . . . .
BEARINGS AND OIL SEALS 1-3. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
CIRCLIPS 1-3. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
CHECKING OF CONNECTIONS 1-4. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
HOW TO USE THE CONVERSION TABLE 1-5. . . . . . . . . . . . . . . . . . . . . . . .
SPECIAL TOOLS 1-6. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

1-1
MOTORCYCLE IDENTIFICATION GEN
INFO
NOTE:
YP100000
GENERAL INFORMATION
MOTORCYCLE IDENTIFICATION
SR100020
FRAME SERIAL NUMBER
The frame serial number 1is stamped into the
right side of the frame.
EB100030
ENGINE SERIAL NUMBER
Theengineserialnumber 1isstampedintothe
crankcase.
Designs and specifications are subject to
change without notice.
MODEL LABEL
The model label 1is affixed under the seat.
This information will be needed to order spare
parts.

1-2
IMPORTANT INFORMATION GEN
INFO
EB101000
IMPORTANT INFORMATION
PREPARATION FOR REMOVAL PROCE-
DURES
1. Removeall dirt, mud, dust and foreign mate-
rial before removal and disassembly.
2. Use proper tools and cleaning equipment.
3. Refer to the “SPECIAL TOOLS” section.
4. When disassembling the machine, always
keep mated parts together. This includes
gears,cylinders, pistons andotherparts that
have been “mated” through normal wear.
Mated parts must always be reused or re-
placed as an assembly.
5. During machine disassembly, clean all parts
and place them in trays in the order of disas-
sembly. This will speed up assembly and al-
low for the correct installation of all parts.
6. Keep all parts away from any source of fire.
NB101010
REPLACEMENT PARTS
1. Use only genuine Yamaha parts for all re-
placements. Use oil and grease recom-
mended by Yamaha for all lubrication jobs.
Other brands may be similar in function and
appearance, but inferior in quality.
EB101020
GASKETS, OIL SEALS AND O-RINGS
1. Replaceallgaskets, sealsand O-ringswhen
overhauling the engine. 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.

1-3
OR
IMPORTANT INFORMATION GEN
INFO
CAUTION:
EB101030
LOCK WASHERS/PLATES AND COTTER
PINS
1. Replace all lock washers/plates and cotter
pins after removal. Bend lock tabs along the
bolt or nut flats after the bolt or nut has been
tightened to specification.
EB101040
BEARINGS AND OIL SEALS
Install bearings and oil seals so that the
manufacturer’s marks or numbers are visible.
Wheninstallingoil seals,applyalightcoatingof
lightweight lithium base grease to the seal lips.
Oil bearings liberally when installing, if ap-
propriate.
1Oil seal
Do not use compressed air to spin the bear-
ings dry. This will damage the bearing sur-
faces.
1Bearing
EB101050
CIRCLIPS
1. Checkallcirclips carefully before reassemb-
ly. Always replace piston pin clips after one
use. Replace distorted circlips. When instal-
ling a circlp 1, make sure that the sharp-
edged corner 2is positioned opposite the
thrust 3it receives. See sectional view.
4Shaft

1-4
CHECKING OF CONNECTIONS GEN
INFO
NOTE:
NOTE:
EB801000
CHECKING OF CONNECTIONS
Dealing with stains, rust, moisture, etc. on the
connector.
1. Disconnect:
Connector
2. Dry each terminal with an air blower.
3. Connect and disconnect the connector two
or three.
4. Pulltheleadto check that it will not come off.
5. If the terminal comes off, bend up the pin 1
and reinsert the terminal into the connector.
6. Connect:
Connector
The two connectors “click” together.
7. Check for continuity with a tester.
If there is no continuity, clean the terminals.
Besuretoperformthesteps1to7listedabove
when checking the wireharness.
For a field remedy, use a contact revitalizer
available on the market.
Use the tester on the connector as shown.

1-5
HOW TO USE THE CONVERSION TABLE GEN
INFO
EB201000
HOW TO USE THE CONVERSION TABLE
All specification data in this manual are listed in Sl and METRIC UNITS.
Use this table to convert METRIC unit data to IMPERIAL unit data.
Ex.
METRIC MULTIPLIER IMP
** mm 0.03937 = ** in
2 mm 0.03937 = 0.08 in
CONVERSION TABLE
METRIC TO IMP
Known Multiplier Result
Torque
m:kg
m:kg
cm:kg
cm:kg
7.233
86.794
0.0723
0.8679
ft:lb
in:lb
ft:lb
in:lb
Weight kg
g2.205 0.03527 lb oz
Distance
km/hr
km
m
m
cm
mm
0.6214
0.6214
3.281
1.094
0.3937
0.03937
mph
mi
ft
yd
in
in
Volume/
Capacity
cc (cm3)
cc (cm3)
lit (liter)
lit (liter)
0.03527
0.06102
0.8799
0.2199
oz (IMP liq.)
cu:in
qt (IMP liq.)
gal (IMP liq.)
Miscellaneous kg/mm
kg/cm2
Centigrade
55.997
14.2234
9/5(_C) + 32
lb/in
psi (lb/in2)
Fahrenheit (_F)

1-6
SPECIAL TOOLS GEN
INFO
EB102000
SPECIAL TOOLS
The following special tools are necessary for complete and accurate tune-up and assembly. Use only
theappropriatespecial tools;this willhelp preventdamagecausedbytheuseofinappropriatetools or
improvised techniques.
When placing an order, refer to the list provided below to avoid any mistakes.
Tool No. Tool name/Usage Illustration
90890-01080
90890-04052 Rotor puller Attachment
This tool is used when removing or installing
the meter gear bush.
90890-01083
90890-01084 Rocker arm shaft puller bolt Weight
These tools are used when removing or
installing the rocker arm shafts.
90890-01268 Ringnut wrench
This tool is used to loosen and tighten the
exhaust and steering ringnut.
90890-01311 Valve adjusting tool
This tool is necessary for adjusting valve
clearance.
90890-01312 Fuel level gauge
This gauge is used to measure the fuel level
in the float chamber.
90890-01367
90890-01400 Fork seal driver weight Fork seal driver attachment (ø30 mm)
This tool is used when installing the fork seal.
90890-01403 Ring nut wrench
This tool is used to loosen and tighten the
steering ring nut.
90890-01701 Sheave holder
This tool is used for holding the secondary
sheave.
90890-01996 Cylinder cup installer set
This tool is used for installing the cylinder
cup to the master cylinder piston.

1-7
SPECIAL TOOLS GEN
INFO
Tool No. Tool name/Usage Illustration
90890-03079 Thickness gauge
This tool is used to measure the valve
clearance.
90890-03081
90890-04082 Compression gauge Adaptor
These tools are used to measure the engine
compression.
90890-03112 Pocket tester
These instruments are invaluable for
checking the electrical system.
90890-03113 Engine tachometer
This tool is needed for detecting engine rpm.
90890-03141 Timing light
This tool is necessary for checking ignition
timing.
90890-04019
90890-04108 Valve spring compressor Attachment
These tools are used when removing or
installing the valve and the valve spring.
90890-04064 Valve guide remover 6 mm
This tool is used to remove the valve guide.
90890-04065 Valve guide reamer 6 mm
This tool is used to rebore the valve guide.
90890-04066 Valve guide installer 6 mm
This tool is needed to install the valve guides
properly.
90890-04086 Clutch holding tool
This tool is used for holding the Clutch Boss.

1-8
SPECIAL TOOLS GEN
INFO
Tool No. Tool name/Usage Illustration
90890-04101 Valve lapper
This tool is used for removing and installing
the lifter and for lapping the valve.
90890-06754 Ignition checker
This instrument is necessary for checking the
ignition system components.
90890-85505 Yamaha bond No.1215
This sealant (bond) is used for crankcase
mating surface, etc.

CHAPTER 2.
SPECIFICATIONS
GENERAL SPECIFICATIONS 2-1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
MAINTENANCE SPECIFICATIONS 2-4. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
ENGINE 2-4. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
CHASSIS 2-10. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
ELECTRICAL 2-13. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
GENERAL TORQUE SPECIFICATIONS 2-15. . . . . . . . . . . . . . . . . . . . . . . . . .
LUBRICATION POINT AND GRADE OF LUBRICANT 2-16. . . . . . . . . . . . .
ENGINE 2-16. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
CHASSIS 2-17. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
LUBRICATION DIAGRAM 2-18. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
CABLE ROUTING 2-20. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .