engine YAMAHA YZ125LC 2003 Owner's Manual

1-16
GEN
INFO
TORQUE-CHECK POINTS
EC1A0013
TORQUE-CHECK POINTS
Frame construction Frame to rear frame
Combined seat and tank Fuel tank to frame
Engine mounting Frame to engine
Engine bracket to engine
Engine bracket to frame
Steering Steering shaft to Steering shaft to frame
handlebar Steering shaft to handle crown
Handle crown to handlebar
Suspension Front Steering shaft to Front fork to handle crown
front fork Front fork to under bracket
Rear For link type Assembly of links
Link to frame
Link to shock absorber
Link to swingarm
Rear Installation of shock Shock absorber to frame
absorber
Rear Installation of swingarm Tightening of pivot shaft
Wheel Installation of wheel Front Tightening of front axle
Tightening of axle holder
Rear Tightening of rear axle
Wheel to sprocket
Brake Front Caliper to front fork
Brake disc to wheel
Tightening of union bolt
Master cylinder to handlebar
Tightening of air bleeder
Rear Brake pedal to frame
Brake disc to wheel
Tighening of union bolt
Master cylinder to frame
Tightening of air bleeder
Fuel system Fuel tank to fuel cock
NOTE:
Concerning the tightening torque, refer to “
MAINTENANCE SPECIFICATIONS” section in
the CHAPTER 2.

1-17
GEN
INFO
CLEANING AND STORAGE
EC1B0000
CLEANING AND STORAGE
EC1B1000
CLEANING
Frequent cleaning of your machine will enhance
its appearance, maintain good overall perfor-
mance, and extend the life of many components.
1. Before washing the machine, block off the
end of the exhaust pipe to prevent water
from entering. A plastic bag secured with a
rubber band may be used for this purpose.
2. If the engine is excessively greasy, apply
some degreaser to it with a paint brush. Do
not apply degreaser to the chain, sprockets,
or wheel axles.
3. Rinse the dirt and degreaser off with a gar-
den hose; use only enough pressure to do
the job.
cC
Excessive hose pressure may cause water
seepage and contamination of wheel bear-
ings, front forks, brakes and transmission
seals. Many expensive repair bills have re-
sulted from improper high pressure deter-
gent applications such as those available
in coin-operated car washers.
4. After the majority of the dirt has been hosed
off, wash all surfaces with warm water and a
mild detergent. Use an old toothbrush to
clean hard-to-reach places.
5. Rinse the machine off immediately with
clean water, and dry all surfaces with a soft
towel or cloth.
6. Immediately after washing, remove excess
water from the chain with a paper towel and
lubricate the chain to prevent rust.
7. Clean the seat with a vinyl upholstery clean-
er to keep the cover pliable and glossy.
8. Automotive wax may be applied to all paint-
ed or chromed surfaces. Avoid combination
cleaner-waxes, as they may contain abra-
sives.
9. After completing the above, start the engine
and allow it to idle for several minutes.

1-18
GEN
INFO
CLEANING AND STORAGE
EC1B2001
STORAGE
If your machine is to be stored for 60 days or
more, some preventive measures must be taken
to avoid deterioration. After cleaning the ma-
chine thoroughly, prepare it for storage as fol-
lows:
1. Drain the fuel tank, fuel lines, and the carbu-
retor float bowl.
2. Remove the spark plug, pour a tablespoon
of SAE 10W-30 motor oil in the spark plug
hole, and reinstall the plug. With the engine
stop switch pushed in, kick the engine over
several times to coat the cylinder walls with
oil.
3. Remove the drive chain, clean it thoroughly
with solvent, and lubricate it. Reinstall the
chain or store it in a plastic bag tied to the
frame.
4. Lubricate all control cables.
5. Block the frame up to raise the wheels off
the ground.
6. Tie a plastic bag over the exhaust pipe out-
let to prevent moisture from entering.
7. If the machine is to be stored in a humid or
salt-air environment, coat all exposed metal
surfaces with a film of light oil. Do not apply
oil to rubber parts or the seat cover.
NOTE:
Make any necessary repairs before the machine
is stored.

2-1
SPECGENERAL SPECIFICATIONS
Model name: YZ125LC (EUROPE)
YZ125R (USA)
YZ125(R) (CDN, AUS, NZ, ZA)
Model code number: 5UN1 (USA, CDN, ZA)
5UN2 (EUROPE)
5UN4 (AUS, NZ)
Dimensions:USA, ZAAUS, NZ EUROPE CDN
Overall length 2,134 mm←2,130 mm←
(84.0 in) (83.9 in)
Overall width 827 mm←←←
(32.6 in)
Overall height 1,318 mm 1,315 mm 1,311 mm 1,315 mm
(51.9 in) (51.8 in) (51.6 in) (51.8 in)
Seat height 993 mm←992 mm←
(39.1 in) (39.1 in)
Wheelbase 1,438 mm←←←
(56.6 in)
Minimum ground clearance 400 mm←398 mm←
(15.7 in) (15.7 in)
Basic weight:
With oil and full fuel tank 94.5 kg (208.3 lb)
Engine:
Engine type Liquid cooled 2-stroke, gasoline
Cylinder arrangement Single cylinder, forward inclined
Displacement 124 cm
3(4.36 lmp oz, 4.19 US oz)
Bore ×Stroke 54 ×54.5 mm (2.126 ×2.146 in)
Compression ratio 8.7~11.0 : 1
Starting system Kick starter
Lubrication system: Premix (30 : 1)(Yamalube 2-R)
Oil type or grade (2-Cycle):
Transmission oil Yamalube 4 (10W-30) or SAE 10W-30 type SE
motor oil
Periodic oil change 0.65 L (0.57 Imp qt, 0.69 US qt)
Total amount 0.70 L (0.62 Imp qt, 0.74 US qt)
Coolant capacity (including all routes): 0.95 L (0.84 Imp qt, 1.00 US qt)
Air filter: Wet type element
Fuel:
Type Except for ZA: Premium unleaded gasoline
only with a research octane
number of 95 or higher
For ZA: Premium gasoline
Tank capacity 8.0 L (1.76 Imp gal, 2.11 US gal)
EC200000
SPECIFICATIONSEC211000
GENERAL SPECIFICATIONS

2-3
SPECMAINTENANCE SPECIFICATIONS
Item Standard Limit
Cylinder head:
Combustion chamber capacity 10.05 cm
3…
(0.354 Imp oz, 0.340 US oz)
Warp limit…
0.03 mm (0.0012 in)
Cylinder:
Bore size 54.000~54.014 mm 54.1 mm (2.130 in)
(2.1260~2.1265 in)
Taper limit…
0.05 mm (0.0020 in)
Out of round limit…
0.01 mm (0.0004 in)
Piston:
Piston size/ 53.957~53.972 mm…
(2.1243~2.1249 in)
Measuring point* 17.5 mm (0.69 in)…
Piston clearance 0.040~0.045 mm 0.1 mm (0.004 in)
(0.0016~0.0018 in)
Piston offset 1.0 mm (0.039 in)/EX-side…
Piston pin:
Piston pin outside diameter 14.995~15.000 mm 14.975 mm
(0.5904~0.5906 in) (0.5896 in)
Piston ring:
Sectional sketch Plain…
B=1.0 mm (0.039 in)…
T=2.35 mm (0.093 in)…
End gap (installed) 0.5~0.7 mm (0.020~0.028 in) 1.2 mm (0.047 in)
Side clearance (installed) 0.035~0.070 mm 0.1 mm (0.004 in)
(0.0014~0.0028 in)
Crankshaft:
Crank width “A” 55.90~55.95 mm …
(2.201~2.203 in)
Runout limit “C” 0.03 mm (0.0012 in) 0.05 mm (0.0020 in)
Connecting rod big end
side clearance “D” 0.20~0.70 mm (0.008~0.028 in)…
Small end free play “F” 0.8~1.0 mm (0.031~0.039 in) 2.0 mm (0.08 in)
Clutch:
Friction plate thickness 2.9~3.1 mm (0.114~0.122 in) 2.8 mm (0.110 in)
Quantity 8 …
Clutch plate thickness 1.5~1.7 mm (0.059~0.067 in) …
Quantity 7 …
Warp limit … 0.2 mm (0.008 in)
Clutch spring free length 41.2 mm (1.622 in) 39.2 mm (1.543 in)
Quantity 5 …
Clutch housing thrust clearance 0.20~0.25 mm (0.008~0.010 in) …
Clutch housing radial clearance 0.015~0.049 mm …
(0.0006~0.0019 in)
Clutch release method Outer pull, rack and pinion pull …
EC212000
MAINTENANCE SPECIFICATIONSEC212100
ENGINE

2-10
SPECMAINTENANCE SPECIFICATIONS
Part to be tightened Thread size Q'tyT ightening torqueNm m•kg ft•lb
Rear brake master cylinder and frame M 6 ×1.0 2 10 1.0 7.2
Rear brake master cylinder cap M 4 ×0.7 2 2 0.2 1.4
Rear brake hose union bolt (caliper) M10 ×1.25 1 30 3.0 22
Rear brake hose union bolt (master cylinder) M10 ×1.25 1 30 3.0 22
Rear wheel axle and nut M20 ×1.5 1 125 12.5 90
Nipple (spoke) – 72 3 0.3 2.2
Driven sprocket and wheel hub M 8 ×1.25 6 42 4.2 30
Disc cover and rear brake caliper M 6 ×1.0 2 7 0.7 5.1
Protector and rear brake caliper M 6 ×1.0 2 7 0.7 5.1
Chain puller adjust bolt and locknut M 8 ×1.25 2 16 1.6 11
Engine mounting:
Engine and frame (front) M10 ×1.25 1 69 6.9 50
Engine and frame (lower) M10 ×1.25 1 69 6.9 50
Engine bracket and frame M 8 ×1.25 2 34 3.4 24
Engine bracket and engine M 8 ×1.25 1 34 3.4 24
Pivot shaft and nut M16 ×1.5 1 85 8.5 61
Relay arm and swingarm M14 ×1.5 1 80 8.0 58
Relay arm and connecting rod M14 ×1.5 1 80 8.0 58
Connecting rod and frame M14 ×1.5 1 80 8.0 58
Rear shock absorber and frame M10 ×1.25 1 56 5.6 40
Rear shock absorber and relay arm M10 ×1.25 1 53 5.3 38
Rear frame and frame (upper) M 8 ×1.25 1 32 3.2 23
Rear frame and frame (lower) M 8 ×1.25 2 29 2.9 21
Swingarm and brake hose holder M 5 ×0.8 4 1 0.1 0.7
Swingarm and patch M 4 ×0.7 4 2 0.2 1.4
Chain tensioner mounting M 8 ×1.25 2 19 1.9 13
Chain support and swingarm M 6 ×1.0 3 7 0.7 5.1
Seal guard and swingarm M 5 ×0.8 4 6 0.6 4.3
Fuel tank mounting M 6 ×1.0 2 10 1.0 7.2
Fuel tank and fuel cock M 6 ×1.0 2 7 0.7 5.1
Fuel tank and seat set bracket M 6 ×1.0 1 7 0.7 5.1
Fuel tank and hooking screw (fitting band) M 6 ×1.0 1 7 0.7 5.1
Fuel tank and fuel tank bracket M 6 ×1.0 4 7 0.7 5.1
Air scoop mounting M 6 ×1.0 6 4 0.4 2.9
Front fender mounting M 6 ×1.0 4 7 0.7 5.1
Rear fender mounting (front) M 6 ×1.0 2 7 0.7 5.1
Rear fender mounting (rear) M 6 ×1.0 2 11 1.1 8.0
Side cover mounting M 6 ×1.0 2 7 0.7 5.1
Seat mounting M 8 ×1.25 2 19 1.9 13
Number plate M 6 ×1.0 1 7 0.7 5.1
NOTE:

- marked portion shall be checked for torque tightening after break-in or before each race.


 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

2-12
SPEC
GENERAL TORQUE SPECIFICATIONS/
DEFINITION OF UNITS
This chart specifies torque for standard faste-
ners with standard I.S.O. pitch threads. Torque
specifications for special components or assem-
blies are included in the applicable sections of
this book. To avoid warpage, tighten multi-faste-
ner assemblies in a crisscross fashion, in pro-
gressive stages, until full torque is reached.
Unless otherwise specified, torque specifications
call for clean, dry threads. Components should
be at room temperature.
A: Distance across flats
B: Outside thread diameter
EC230000
DEFINITION OF UNITS
EC220001
GENERAL TORQUE SPECIFICATIONS
A B TORQUE SPECIFICATION
(Nut) (Bolt)
Nm m•kg ft•lb
10 mm 6 mm 6 0.6 4.3
12 mm 8 mm 15 1.5 11
14 mm 10 mm 30 3.0 22
17 mm 12 mm 55 5.5 40
19 mm 14 mm 85 8.5 61
22 mm 16 mm 130 13 94
Unit Read Definition Measure
mm milimeter 10-
3meter Length
cm centimeter 10-2meter Length
kg kilogram 103gram Weight
N Newton 1 kg ×m/sec2Force
Nm Newton meter N ×m Torque
m•kg Meter kilogrma m ×kg Torque
Pa Pascal N/m2Pressure
N/mm Newton per millimeter N/mm Spring rate
L Liter — Volume or capacity
cm3Cubic centimeter — Volume or capacity
r/min Revolution per minute — Engine speed

2-13
SPECCABLE ROUTING DIAGRAM
EC240000
CABLE ROUTING DIAGRAM
1Brake hose
2Cable guide
3“ENGINE STOP” button lead
4Fuel tank breather hose
5Clamp
6Throttle cable
7Air vent hose (right)
8Air vent hose (left)
9Transmission oil breather hose
0Overflow hose
qYPVS breather hose
wRadiator breather hose
eCDI magneto lead
rWireharnessAPass the throttle cable and
“ENGINE STOP” button lead
into the cable guide. Align
with the cable guide the
front end of the tape on the
throttle cable.
BPass the fuel tank breather
hose between the handlebar
and tension bar, then insert
its end into the hole of the
number plate.
CPass the throttle cable and
“ENGINE STOP” button lead
over the radiator hose.
DClamp the throttle cable,
“ENGINE STOP” button lead
and wireharness to the main
pipe. With the clamp ends
downward, tighten the throttle
cable to the extent that it
moves smoothly.
EClamp the “ENGINE STOP”
button lead (where there is no
protector), wireharness and
throttle cable all together to the
main pipe with the clamp ends
downward.FClamp the CDI magneto lead
on the upper part of
the frame gusset at its
protecting tube.
GClamp the throttle cable and
wireharness to the main pipe.
With the clamp ends downward,
tighten the throttle cable to the
extent that it moves smoothly.
HPass the air vent hose at
the rear of the throttle cable.
IPass the transmission oil
breather hose, air vent hoses
and overflow hose between
the frame and connecting rod.
JPass the radiator breather
hose and YPVS breather hose
outside the engine bracket
and inside the down tube. Then
pass the radiator breather
hose inside the YPVS
breather hose.
KClamp the radiator breather
hose and CDI magneto lead
on the rear of the down-tube.

2-13
SPEC
SCHEMA DE CHEMINEMENT DES CABLES
KABELFÜHRUNGSÜBERSICHTPLAN
DIAGRAMMA DEL PASSAGGIO DEI CAVI
KABELFÜHRUNGSÜBER-
SICHTPLAN
1Bremsschlauch
2Kabelführung
3Leitungskabel des Motorstoppknopfes
„ENGINE STOP“
4Kraftstofftank-Belüftungsschlauch
5Klemme
6Gasseil
7Belüftungsschlauch (Rechts)
8Belüftungsschlauch (Links)
9Getriebeöl-Belüftungsschlauch
0Überlaufschlauch
qYPVS-Belüftungsschlauch
wKühler-Belüftungsschlauch
eLeitungskabel des CDI-Magnetzünders
rKabelbaum
ADas Gasseil und den Leitungsdraht der
„ENGINE STOP“-Taste durch die
Kabelführing führen.
Vorderes Bandende am Gaskabel mit
der Kabelführung ausrichten.
BDen Kraftstofftank-Belüftungsschlauch
zwischen der Lenkstange und der Zug-
stange durchführen und danach sein
Ende in die Bohrung des Nummern-
schildes einsatzen.
CDas Gasseil und das Leitungskabel des
Motorstoppknopfes „ENGINE STOP“
über dem Kühlerschlauch durchführen.
DGaskabel, Motorstoppknopf „ENGINE
STOP“ und Kabelbaum am Hauptrohr
festklemmen. Mit den Schellenenden
nach unten zieht man das Gaskabelen-
de so fest, dass es sich reibungslos
bewegt.
ELeitung des Motorstoppknopfes „ENGI-
NE STOP“ (wenn kein Schutz vorhan-
den ist), Kabelbaum und Gaskabel
gemeinsam am Hauptrohr festklem-
men, mit den Schellenenden nach
unten.
FDas Leitengskabel des CDI-Magnetzün-
ders am oberen Teil der Rehmensfütze
an ihrem Schutzrohr festklemmen.
GGaskabel und Kabelbaum am Haupt-
rohr festklemmen. Mit den Enden der
Schelle nach unten zeigend, zieht man
das Gaskabel so fest, dass es sich rei-
bungslos bewegt.
HDen Belüftungsschlauch hinter dem
Gasseil durchführen.
IDen Getriebeöl-Belüftungsschlauch, die
Belüftungsschläuche und den Üderlauf-
schlauch zwischen dem Rahmen und
der Verbindungsstange durchführen.
JKühlerbelüftungsschlauch und YPVS-
Belüftungsschlauch an der Aussenseite
der Motorhalterung und an den Innen-
seite des Abwärtsrohrs führen. Dann
Kühlerbelüftungsschlauch in den YPVS-
Belüftungsschlauch einführen.
KDen Kühler-Belüftungsschlauch und
das Leitungskabel des CDI-Magnetzün-
ders an der Rückseite des Fallrohres
festklemmen.
SCHEMA DE
CHEMINEMENT DES
CABLES
1Tuyau de frein
2Guide de câble
3Fil de bouton d’arrêt du moteur “ENGINE
STOP”
4Tuyau de reniflard de réservoir à essence
5Bride
6Câble d’accélérateur
7Tuyau de ventilation (droit)
8Tuyau de ventilation (gauche)
9Tuyau de reniflard d’huile de boîte de
vitesses
0Tube de trop-plein
qTube de reniflard YPVS
wTuyau de reniflard de radiateur
eFil de magnéto CDI
rFaisceau de fils
åFaire passer le câble d’accélérateur et le fil
du bouton “ENGINE STOP” (arrêt
moteur) dans le guidage de câble.
Aligner sur le guide-câble l’extrémité
avant du ruban du câble d’accélérateur.
∫Faire passer le tuyau de reniflard du réser-
voir à carburant entre le guidon et la barre
de tension, puis l’insérer dans l’orifice de
la plaque minéralogique.
çFaire passer le câble d’accélérateur et le fil
du bouton d’arrêt moteur “ENGINE
STOP” au-dessus de la durit de radiateur.
∂Fixez le câble d’accélérateur, le fil du
bouton “ENGINE STOP” et le faisceau
de fils sur le tube principal. Les extrémi-
tés de la bride étant orientées vers le bas,
serrez le câble d’accélérateur de manière
à ce qu’il se déplace aisément.
´Fixez le fil du bouton “ENGINE STOP”,
le faisceau de fils et le câbled’accéléra-
teur ensemble sur le tube principal avec
les extrémités de la bride orientées vers
le bas.
ƒFixer le fil de magnéto de CDI sur la partie
supérieure du couvre-joint du tube de pro-
tection.
©Bridez le câble d’accélérateur et le fais-
ceau de fils sur le tube principal. En
orientant les extrémités de la bride vers
le bas, serrez le câble d’accélérateur de
façon à ce qu’il bouge facilement.
˙Faire passer le tuyau de ventilation à
l’arrière du câble d’accélérateur.
ˆFaire passer le tube reniflard d’huile de
transmission, les tubes d’aération et le tube
de trop-plein.
∆Faites passer le tuyau du reniflard du
radiateur et le tuyau du reniflard de
l’YPVS à l’extérieur du support du
moteur et à l’intérieur du tube inférieur.
Faites ensuite passer le tuyau du reniflard
du radiateur à l’intérieur tuyau du reni-
flard de l’YPVS.
˚Fixer avec un collier le tuyau de reniflard
du radiateur et le fil de magnéto CDI.
IC240000
DIAGRAMMA DEL
PASSAGGIO DEI CAVI
1Tubo flessibile del freno
2Guida per cavi
3Conduttore del pulsante “ARRESTO
MOTORE”
4Sfiato del serbatoio del carburante
5Brida
6Cavo dell’acceleratore
7Tubo flessibile dello sfiatatoio dell’aria
(destro)
8Tubo flessibile dello sfiatatoio dell’aria
(sinistro)
9Sfiato dell’olio per trasmissioni
0Tubo flessibile di troppopieno
qSfiato YPVS
wSfiato del radiatore
eConduttore del magneto CDI
rComplesso conduttori
åFar passare il cavo dell’acceleratore e il
conduttore del pulsante “ARRESTO
MOTORE” nella guida per cavi.
Allineare con la guida per cavi l’estre-
mità anteriore del nastro sul cavo dell'ac-
celeratore.
∫Far passare lo sfiato del serbatoio puran-
te fra il manubrio e il tirante, quindi inse-
rirne l’estremità nel foro della targa.
çFar passare il cavo dell’acceleratore e il
conduttore del pulsante “ARRESTO
MOTORE” sopra il manicotto flessibile
del radiatore.
∂Assicurare al tubo principale il cavo
dell’acceleratore e il conduttore e il
cablaggio preassemblato del pulsante
“ARRESTO MOTORE”. Con le estre-
mità della brida verso il basso, assicurare
il cavo dell’acceleratore in modo che
possa scorrere facilmente.
´Assicurare tutti insieme al tubo principa-
le, con le estremità della brida verso il
basso, il conduttore del pulsante “ARRE-
STO MOTORE” (dove non vi è prote-
zione), il cablaggio preassemblato e il
cavo dell’acceleratore.
ƒBloccare il conduttore del magnete CDI
sulla parte superiore del fazzoletto del
telaio in corrispondeza del suo tubo di
protezione.
©Assicurare al tubo principale il cavo del-
l'acceleratore e il cablaggio preassembla-
to. Con le estremità della brida rivolte
verso il basso, assicurare il cavo dell'ac-
celeratore in modo che possa scorrere
facilmente.
˙Far passare il tubo flessibile dello sfiata-
toio dell’aria sul retro del cavo dell’acce-
leratore.
ˆFar passare lo sfiato dell’olio per tra-
smissioni, i tubi flessibili degli sfiatatoi
dell’aria e il tubo flessibile di troppopie-
no fra il telaio e la leva di rinvio.
∆Far passare lo sfiato del radiatore e lo
sfiato YPVS fuori dalla staffa del motore
dentro il tubo inferiore. Quindi far passa-
re lo sfiato del radiatore dentro lo sfiato
dell’YPVS.
˚Bloccare lo sfiato del radiatore e il con-
duttore del magnete CDI sul retro del
tubo rivolto verso il basso.

2-17
SPECCABLE ROUTING DIAGRAM
AInstall the brake hose so that its pipe portion
directs as shown and lightly touches the
projection on the master cylinder.
BPass the “ENGINE STOP” button lead in
the middle of the clutch holder.
CPass the clutch cable in front of the throttle
cable.
DClamp the “ENGINE STOP” button lead to
the handlebar to 3 clicks.
EPass the brake hose in front of the number
plate and through the cable guide.
FCross the clutch cable and throttle cable
over the number plate boss. 1Brake hose
2Master cylinder
3“ENGINE STOP” button lead
4“ENGINE STOP” button
5Throttle cable
6Clutch cable
7Clamp
8Cable guide