2002 YAMAHA YZ125LC engine

1-14
GEN
INFO
STARTING AND BREAK-IN
EC194001
BREAK-IN PROCEDURES
1. Before starting the engine, fill the fuel tank
with a break-in oil-fuel mixture as follows.
2. Perform the pre-operation checks on the
machine.
3. Start and warm up the engine. Check the
idle speed, and check the operation of the
controls and the “ENGINE STOP” button.
4. Operate the machine in the lower gears at
moderate throttle openings for five to eight
minutes. Stop and check the spark plug
condition; it will show a rich condition during
break-in.
5. Allow the engine to cool. Restart the engine
and operate the machine as in the step
above for five minutes. Then, very briefly
shift to the higher gears and check full-throt-
tle response. Stop and check the spark
plug.
6. After again allowing the engine to cool,
restart and run the machine for five more
minutes. Full throttle and the higher gears
may be used, but sustained full-throttle op-
eration should be avoided. Check the spark
plug condition.
7. Allow the engine to cool, remove the top
end, and inspect the piston and cylinder.
Remove any high spots on the piston with
#600 grit wet sandpaper. Clean all compo-
nents and carefully reassemble the top end.
8. Drain the break-in oil-fuel mixture from the
fuel tank and refill with the specified mix.
9. Restart the engine and check the operation
of the machine throughout its entire operat-
ing range. Stop and check the spark plug
condition. Restart the machine and operate
it for about 10 to 15 more minutes. The ma-
chine will now be ready to race.
Mixing oil: Mixing ratio:
Yamalube “2-R” 15:1
5NY-9-30-1B 5/23/01 8:12 PM Page 6

1-14
GEN
INFO
MISE EN MARCHE ET RODAGE
STARTEN UND EINFAHREN
AVVIAMENTO E RODAGGIO
EINFAHRVORGÄNGE1. Vor dem Starten des Motors, den
Kraftstofftank für das Einfahren mit
einem Benzin/Öl-Gemisch wie dar-
gestellt füllen.
2. Die unter „Prüfungen vor Inbetrieb-
nahme“ aufgeführten Kotrollen aus-
führen.
3. Den Motor starten und warmlaufen
lassen. Die Leerlaufdrehzahl kon-
trollieren und die Funktion der
Bedienungselemente und des
Motorstoppknopfes „ENGINE
STOP“ prüfen.
4. Die Maschine in den unteren Gän-
gen bei gemäßigter Drosselöffnung
füf fünf bis acht Minuten fahren. Den
Motor danach abschalten und den
Zustand der Zündkerze kontrollie-
ren; während des Einfahrens sollte
die Zündkerze leicht verölt (fettes
Gemisch) sein.
5. Den Motor abkühlen lassen. Den
Motor wieder starten und die
Maschine für etwa fünf Minuten
unter den gleichen Bedingungen
betreiben, wie sie oben beschrieben
wurden. Danach jeweils kurz in die
höheren Gänge schalten und das
Ansprechen auf Vollgas kontrollie-
ren. Den Motor wieder abschalten
und nochmals die Zündkerze kon-
trollieren.
6. Den Motor abkühlen lassen, danach
wieder starten und die Maschine
nochmals für fünf Minuten betreiben.
Nun dürfen die höheren Gänge
auch bei Vollgas eingesetzt werden,
wobei jedoch längeres Vollgasfah-
ren zu vermeiden ist. Anschließend
den Zustand der Zündkerze prüfen.
7. Den Motor abkühlen lassen, den
Zylinderkopf ausbauen und Kolben
und Zylinder kontrollieren. Den Kol-
ben ggf. mit Schmirgelleinen der
Körnung 600 glätten. Alle Bauteile
reinigen und vorsichtig wieder ein-
bauen.
8. Das Benzin/Öl-Gemisch für das Ein-
fahren aus dem Kraftstofftank ent-
leeren und das vorgeschriebene
Gemisch einfüllen.
9. Den Motor starten und die Betriebs-
bedingungen der Maschine im
gesamten Betriebsbereich überprü-
fen. Den Motor abschalten und den
Zustand der Zündkerze kontrollie-
ren. Den Motor wieder starten und
die Maschine für etwa 10 bis 15
Minuten betreiben. Danach ist die
Maschine einsatzbereit für Rennen.
PROCEDURE DE RODAGE
1. Avant de lancer le moteur, rem-
plissez le réservoir d’un mélange
essence-huile de rodage de propor-
tion si dessous.
2. Exécutez le contrôle avant utilisa-
tion de la machine.
3. Lancez le moteur et laissez-le se
réchauffer. Vérifiez le régime de
ralenti, le fonctionnement des
commandes et l’efficacité du bou-
ton d’arrêt du moteur “ENGINE
STOP”.
4. Pilotez la machine sur les rapports
inférieurs et à régime modéré
durant les cinq à huit premières
minutes. Arrêtez-vous et vérifiez
l’état de la bougie; elle devrait
donner des indices de richesse
durant le rodage.
5. Laissez le moteur se refroidir.
Remettez le moteur en marche et
pilotez comme ci-dessus pendant
cinq minutes. Passez brièvement
sur les rapports supérieurs et véri-
fiez la réponse à pleine accéléra-
tion. Arrêtez-vous et revérifiez la
bougie.
6. A nouveau, laissez le moteur se
refroidir. Redémarrez et pilotez
pendant cinq nouvelles minutes.
Cette fois, vous pouvez rouler à
pleins gaz sur les rapports supé-
rieurs, mais évitez une marche
soutenue à pleine vitesse. Vérifiez
l’état de la bougie.
7. Laissez le moteur se refroidir,
déposez la culasse et le cylindre, et
examinez piston et cylindre. Elimi-
nez les points élevés au papier de
verre humide No. 600. Nettoyez
tous les éléments puis remontez
soigneusement le moteur.
8. Videz le mélange essence-huile de
rodage du réservoir et remplissez-
le du mélange prescrit.
9. Remettez le moteur en marche et
vérifiez son fonctionnement à tous
les régimes. Arrêtez et vérifiez la
bougie. Relancez le moteur et pilo-
tez la machine pendant 10 à 15
minutes supplémentaires. Elle sera
alors prête pour la course.IC194001PROCEDURE DI RODAGGIO
1. Prima di avviare il motore, riempi-
re il serbatorio del carburante con
una miscela di olio-carburante per
rodaggio come segue.
2. Eseguire i controlli sul veicolo
prima del funzionamento.
3. Avviare e scaldare il motore. Con-
trollare il numero di giri al minimo
e controllare il funzionamento dei
comandi e del pulsante “ARRE-
STO MOTORE”.
4. Azionare il veicolo alle marce
basse con aperture moderate della
valvola a farfalla per cinque-otto
minuti. Arrestarlo e controllare le
condizioni della candela; durante il
rodaggio presenterà condicche.
5. Far raffreddare il motore. Riavvia-
re il motore e far funzionare il vei-
colo come descritto nel punto pre-
cedente per cinque minuti. Quindi,
passare per brevissimo tempo alle
marce alte e controllare la risposta
con la valvola a farfalla completa-
mente aperta. Arrestarlo e control-
lare la candela.
6. Dopo avere fatto raffreddare anco-
ra il motore, riavviare e far girare
il veicolo per altri cinque minuti.
Si possono usare la valvola a far-
falla completamente aperta e le
marce alte, ma si dovrebbe evitare
un funzionamento prolungato con
la valvola a farfalla completamen-
te aperta. Controllare le condizioni
della candela.
7. Far raffreddare il motore, togliere
l’estremità superiore e ispezionare
il pistone e il cilindro. Togliere
eventuali irregolarità sul pistone
con carta vetrata bagnata di grana
No. 600. Pulire tutti i componenti
e rimontare con cautela l’estremità
superiore.
8. Scaricare la miscela di olio-carbu-
rante di rodaggio dal serbatoio del
carburante e riempirlo con la
miscela specificata.
9. Riavviare il motore e controllare il
funzionamento del veicolo per
tutta la gamma di funzionamento.
Arrestarlo e controllare le condi-
zioni della candela. Riavviare il
veicolo e farlo funzionare per altri
10-15 minuti circa. Il veicolo sarà
ora pronto per la gara.
Huile de Proportions
Mélange: de Mélange:
Yamalube
“2-R” 15 : 1Olio per Rapporto di
miscela:
miscelazione:Yamalube
“2-R” 15 : 1
Mischöl: Misch-
verhältnis:
Yamalube
„2-R“ 15 : 1
5NY-9-30-1B 5/23/01 8:12 PM Page 7

1-15
GEN
INFO
STARTING AND BREAK-IN
cC
9
After the break-in or before each race, you
must check the entire machine for loose fit-
tings and fasteners as per “TORQUE-
CHECK POINTS”.
Tighten all such fasteners as required.
9When any of the following parts have been
replaced, they must be broken in.
CYLINDER AND CRANKSHAFT:
About one hour of break-in operation is
necessary.
PISTON, RING AND GEARS:
These parts require about 30 minutes of
break-in operation at half-throttle or less.
Observe the condition of the engine careful-
ly during operation.
5NY-9-30-1B 5/23/01 8:12 PM Page 8

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.
5NY-9-30-1B 5/23/01 8:12 PM Page 10

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.
5NY-9-30-1B 5/23/01 8:12 PM Page 14

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.
5NY-9-30-1B 5/23/01 8:12 PM Page 16

2-1
SPECGENERAL SPECIFICATIONS
Model name: YZ125LC (EUROPE)
YZ125P1 (USA)
YZ125(P) (CDN, AUS, NZ, ZA)
Model code number: 5NY1 (USA, CDN, ZA)
5NY2 (EUROPE)
5NY4 (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 95.0 kg (209.4 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 8.7~10.8 : 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
5NY-9-30-2A 5/24/01 8:03 PM Page 2

2-3
SPECMAINTENANCE SPECIFICATIONS
Item Standard Limit
Cylinder head:
Combustion chamber capacity 10.2 cm
3…
(0.359 Imp oz, 0.345 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
5NY-9-30-2A 5/24/01 8:03 PM Page 4