Yamaha SR125'99 3MW-AE3 User manual

FOREWORD
This Supplementary Service Manual has been prepared to introduce new service and data for the
SR125 ’99. For complete service information procedures it is necessary to use this Supplementary
Service Manual together with the following manual.
SR125 SERVICE MANUAL: 3MW-AE1
SR125 SUPPLEMENTARY SERVICE MANUAL: 3MW-AE2
SR125 ’99
SUPPLEMENTARY
SERVICE MANUAL
1998 by Yamaha Motor Co., Ltd.
First Edition, October 1998
Any reproduction or unauthorized use
without the written permission of
Yamaha Motor Co., Ltd. is expressly
prohibited.

NOTE:
CAUTION:
EB001000
NOTICE
This manual was produced by the Yamaha Motor Company 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,
so it is assumed that anyone who uses this book to perform maintenance and repairs on Yamaha mo-
torcycleshasabasicunderstandingofthemechanicalideasandtheproceduresofmotorcyclerepair.
Repairs attempted by anyone without this knowledge are likely to render the motorcycle unsafe and
unfit for use.
YamahaMotorCompany,Ltd.iscontinuallystrivingtoimproveallitsmodels.Modificationsandsignifi-
cant changes in specifications or procedures will be forwarded to all authorized Yamaha dealers and
will appear in future editions 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!
Failuretofollow WARNINGinstructionscouldresult insevereinjuryordeathto
thescooteroperator,abystanderoraperson inspecting orrepairingthescoot-
er.
ACAUTIONindicatesspecialprecautionsthatmustbe taken to avoid damage
to the scooter.
NOTE: A NOTE provides key information to make procedures easier or clearer.

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2
6
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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
Tohepsidentifypartsandclarifyproceduresteps,thereareexplodeddiagramsatstartofeachremov-
al 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. Ajob instructionchart 7accompaniestheexplodeddiagram,providingthe orderofjobs,namesof
parts, notes in jobs, etc.
5. Forjobsrequiring more information, the step-by-step formatsupplements8 are given in addition to
the exploded diagram and the job instruction chart.

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1
3
5
7
9
2
4
8
6
24 25
2321
19 2018
16 1715
1413
11 12
10
GEN
INFO SPEC
ENG
CARB
ELECCHAS
COOL
INSP
ADJ
TRBL
SHTG
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
5Cooling system
6Carburetion
7Chassis
8Electrical
9Troubleshooting
Illustrated symbols 10 to 17 are used to identify the
specifications appearing in the text.
10 Possible to maintain with engine mounted
11 Filling fluid
12 Lubricant
13 Special tool
14 Tightening
15 Wear limit, clearance
16 Engine speed
17 Ω, V, A
Illustratedsymbols 18 to 23 intheexplodeddia-
grams indicate the types of lubricants and lu-
brication points.
18 Apply engine oil
19 Apply gear oil
20 Apply molybdenum disulfide oil
21 Apply wheel bearing grease
22 Apply lightweight lithium-soap base grease
23 Apply molybdenum disulfide grease
Illustratedsymbols 24 to 25 intheexplodeddia-
gramsindicatethewheretoapplylockingagent
24 and when to install new parts 25 .
24 Apply locking agent (LOCTITE)
25 Use new one

CONTENTS
GENERAL SPECIFICATIONS
GENERAL SPECIFICATIONS 1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
MAINTENANCE SPECIFICATIONS 2. . . . . . . . . . . . . . . . . . . . . . . . . . .
ENGINE 2. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
CHASSIS 2. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
ELECTRICAL 2. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
TIGHTENING TORQUES 3. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
ENGINE 3. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
CHASSIS 3. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
CABLE ROUTING 4. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
PERIODIC INSPECTIONS AND ADJUSTMENTS
CHECKING AND ADJUSTING THE STEERING HEAD 9. . . . . . . . . . . . .
CHECKING AND ADJUSTING THE STEERING HEAD 9. . . . . . . . .
ENGINE OVERHAUL
CYLINDER HEAD 11. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
CYLINDER HEAD 11. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
CHECKING THE TIMING CHAIN TENSIONER 12. . . . . . . . . . . . . . . .
CYLINDER HEAD INSTALLATION 12. . . . . . . . . . . . . . . . . . . . . . . . . . .
CHASSIS
STEERING 15. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
UNDER BRACKET 15. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
’99 SR125 WIRING DIAGRAM

–1–
GENERAL SPECIFICATIONS SPEC
SPECIFICATIONS
GENERAL SPECIFICATIONS
Model SR125
Model code: 3MW8
Dimensions:
Overall height 1,100 mm
Chassis:
Caster angle
Trail 26.75
90 mm
Wheel travel:
Rear wheel travel 76 mm
Bulb wattage quantity:
Headlight
Auxiliary light
Tail/brake light
Flasher light
Meter light
High beam indicator
Neutral indicator
Turn indicator
12 V 60 W/55 W 1
12 V 4 W 1
12 V 5 W/21 W 1
12 V 21 W 4
14 V 3 W 1
12 V 1.7 W 1
12 V 1.7 W 1
12 V 1.7 W 1

–2–
MAINTENANCE SPECIFICATIONS SPEC
MAINTENANCE SPECIFICATIONS
ENGINE
Item Standard Limit
Cam chain:
Cam chain type/No. of links
Cam chain adjustment DID 25SH/104 ENDLESS
Automatic
SSS
SSS
Carburetor:
Engine idle speed 1,300 – 1,400 rpm SSS
CHASSIS
Item Standard Limit
Steering system:
Steering bearing type Angular bearing SSS
Front suspension:
Fork spring free length
Fitting length
Oil capacity
Oil level
Oil grade
353.4 mm
338.4 mm
0.187 L (187 cm3)
138 mm
Fork oil 10 W or equivalent
321 mm
SSS
SSS
SSS
SSS
ELECTRICAL
Item Standard Limit
Ignition coil:
Primary winding resistance
Secondary winding resistance 0.184 – 0.276 Ωat 20_C
6.32 – 9.48 kΩat 20_C
SSS
SSS
Flasher relay:
Type
Model/manufacturer
Flasher frequency
Full transistor type
FE246BH/DENSO
75 – 95 cycle/min
SSS
SSS
SSS

–3–
MAINTENANCE SPECIFICATIONS SPEC
NOTE:
TIGHTENING TORQUES
ENGINE
Part to be tightened Part name Thread
size
Q’ty Tightening
torque Remarks
g
size
y
Nm mSkg
Timing chain tensioner bolt
Timing drain tensioner cap bolt Bolt Bolt 2 110 10 0.1 0.1
CHASSIS
Part to be tightened Thread size Tightening
torque Remarks
g
Nm mSkg
Handle crown and front fork
Handle crown and steering shaft
Handlebar holder (under and upper)
Steering ring nut
M8
M22
M8
M25
19
110
20
4
1.9
11.0
2.0
0.4 Refer to NOTE
1. First,tighten the ring nut to approximately 38Nm (3.8mSkg)with atorque wrench, thenloosen the
ring nut completely.
2. Retighten the ring nut to specification.

–4–
CABLE ROUTING SPEC
12 Wireharness
13 Horn lead
14 Headlight earth lead
15 Auxilialy light lead
16 Meter lead
A Fasterthehandlebarswitchlead
(leftand right)frontbrake switch
lead clutch switch lead to the
handlebar with a band.
B Don’t contact the horn and wire-
harness.
C To auxiliary light.
D To headlight.
CABLE ROUTING
1Speed meter cable
2Handlebar switch lead (left)
3Main switch lead
4Front brake switch lead
5Throttle cable
6Brake hose
7Handlebar switch lead (right)
8Clutch cable
9Clutch switch lead
10 Right flasher lead
11 Left flasher lead

–5–
CABLE ROUTING SPEC
13 Clutch cable guide
14 Right handlebar switch lead
15 Front brake switch lead
16 Clutch switch lead
17 Clutch cable
18 Rear stop switch
19 Sidestand relay
20 Battery breather hose
A Aligntheclamptothewhitetape
on the wireharness.
B Route the brake hose through
the brake hose holder.
C Route the clutch cable through
the clutch cable guide.
D Route the throttle cable, front
brake switch lead handlebar
switch lead through the guide.
1Flasher relay
2Clamp
3Wireharness
4High tension cord
5Collar
6Ignition coil
7Earth lead
8Ignition coil lead
9Throttle cable
10 Brake hose
11 Brake hose holder
12 Wire guide

–6–
CABLE ROUTING SPEC
E Clamp the clutch cable to the
down tube of the frame.
F Cover the sack to the couplers.

–7–
1Pick up coil lead
2Neutral switch lead
3C.D.I unit
4Rear flasher lead (right)
5Rear flasher lead (left)
6Tail/Brake light lead
7Clutch switch lead
8Wireharness
9Clamp
10 Throttle cable
11 Thermo switch lead
12 Thermo switch
A Fasten the junction to the wire-
harness with a band and cut the
end of band. (except for ignition
coil lead and earth lead.)
B Clamp the sidestand switch
lead, battery negative lead and
cut the end.
C Route the battery positive lead
between air filter case and mud
guardsetthebatterypositiveter-
minal.
CABLE ROUTING SPEC
13 Battery negative lead
14 Starter motor lead
15 Rectifier/Regulator
16 Starter relay
17 Battery positive lead
18 Side stand switch lead
19 Side stand switch
20 Clutch cable
21 Wire guide
22 Brake hose
23 Brake hose holder
24 Wire holder
25 Speed meter cable
26 Handlebar switch lead

–8–
H Route the brake hose through
the brake hose holder.
I Clamp the speed meter cable to
the under bracket and through
the wire holder of front fender.
CABLE ROUTING SPEC
D Routetheleadsinsidetheframe
bracket.
E Clamp the starter relay lead rec-
tifier/regulator lead and side-
stand switch lead.
F Clamp the rectifier/regulator
lead.
G Fastentheleadswitin40mfrom
rectifire/regulator with a band.

–9–
CHECKING AND ADJUSTING THE STEERING HEAD INSP
ADJ
WARNING
NOTE:
EB304130
CHECKING AND ADJUSTING THE STEER-
ING HEAD
1. Stand the motorcycle on a level surface.
Securely support the motorcycle so that
there is no danger of it falling over.
Placethemotorcycleonasuitablestandsothat
the front wheel is elevated.
2. Check:
Ssteering head
Grasp the bottom of the front fork legs and
gently rock the front fork.
Looseness/binding Adjust the steering
head.
3. Remove:
Shandlebar 1
4. Loosen:
Supper bracket pinch bolts 1
5. Remove:
Ssteering stem nut 2
Swasher 3
6. Remove:
Sspeed meter 1
Supper bracket 2

–10–
CHECKING AND ADJUSTING THE STEERING HEAD INSP
ADJ
NOTE:
WARNING
NOTE:
110 Nm (11.0 mSkg)
26 Nm (2.6 mSkg)
6.Adjust:
Ssteering head
a. Remove the lock washer 1, the upper ring
nut 2, and the rubber washer 3.
b. Loosenthelowerringnut 4andthentighten
it to specification with a ring nut wrench 5.
Set the torque wrench at a right angle to the
steering nut wrench.
Steering nut wrench
90890-01268
Lower ring nut (initial tightening
torque)
38 Nm (3.8 mSkg)
c. Loosen the lower ring nut completely, then
tighten it to specification.
Do not overtighten the lower ring nut.
Lower ring nut (final tightening
torque)
4 Nm (0.4 mSkg)
d. Check the steering head for looseness or
bindingby turning the frontfork all the wayin
both directions. If any binding is felt, remove
the lower bracket and check the upper and
lower bearings.
Refer to “STEERING HEAD” in chapter 6.
e. Install the rubber washer 3.
f. Install the upper ring nut 2.
g. Finger tighten the upper ring nut 2, then
align the slots of both ring nuts. If necessary,
hold the lower ring nut and tighten the upper
ring nut until their slots are aligned.
h. Install the lock washer 1.
Make sure that the lock washer tabs asit cor-
rectly in the ring nut slots b.
7. Install:
Ssteering stem nut
Supper bracket pinch bolt

–11–
CYLINDER HEAD ENG
Order Job name/Part name Q’ty Remarks
1
2
3
4
5
6
7
Cylinder head removal
Timing chain tensioner assembly
Cam sprocket/Timing chain
Ignition coil
Cylinder head
Dowel pins
Gasket
Cylinder head gasket
1
1/1
1
1
3
1
1
Remove the parts in order.
Reverse the removal procedure for
installation.
Refer to “CYLINDER HEAD
INSTALLATION” section.
Refer to “CYLINDER HEAD
REMOVAL/INSTALLATION” section.
22 Nm (2.2 mSkg)
20 Nm (2.0 mSkg)
60 Nm (6.0 mSkg)
10 Nm (1.0 mSkg)
CYLINDER HEAD

–12–
CYLINDER HEAD ENG
NOTE:
New
New
22 Nm (2.2 mSkg)M8 (1 X4)
20 Nm (2.0 mSkg)M8 (5 X6)
NOTE:
EB401430
CHECKINGTHETIMINGCHAINTENSIONER
1. Check:
Stiming chain tensioner
Cracks/damage/rough movement Re-
place.
a. Lightly press the timing chain tensioner rod
into the timing chain tensioner housing by
hand.
While pressing the timing chain tensioner rod,
windit clockwise with a thin screwdriver 1until
it stops.
b. Remove the screwdriver and slowly release
the timing chain tensioner rod.
c. Makesurethatthetimingchaintensionerrod
comes out of the timing chain tensioner
housing smoothly. If there is rough move-
ment, replace the timing chain tensioner.
SR********
CYLINDER HEAD INSTALLATION
1. Install:
Sdowel pins 1
Sgasket 2
Sgasket (cylinder head) 3
2. Install:
Scylinder head
SApply engine oil onto the nut threads.
STighten the bolts starting with the lowest num-
bered one.