radiator YAMAHA YZ125LC 2011 User Guide

3-2
MAINTENANCE INTERVALS
ROTOR NUT
Retighten●●
MUFFLER
Inspect●●
Clean●
Retighten●●
Replace fiber●** When the exhaust sound be-
comes louder or when a per-
formance drop is felt
CRANK
Inspect and clean●●
CARBURETOR
Inspect, adjust and clean●●
SPARK PLUG
Inspect and clean●●
Replace●
DRIVE CHAINUse chain lube.
Lubricate, slack, alignment●●Chain slack: 48–58 mm (1.9–
2.3 in)
Replace●
COOLING SYSTEM
Check coolant level and
leakage●●
Check radiator cap opera-
tion●
Replace coolant●Every two years
Inspect hoses●
OUTSIDE NUTS AND
BOLTS
Retighten●●Refer to "STARTING AND
BREAK-IN" section in the
CHAPTER 1.
AIR FILTER
Clean and lubricate●●Use foam air-filter oil or equiv-
alent oil.
Replace●
FRAME
Clean and inspect●●
FUEL TANK, COCK
Clean and inspect●● ItemAfter
break-in
Every
race
(about
2.5
hours)Every
third
(about
7.5
hours)Every
fifth
(about
12.5
hours)
As re-
quiredRemarks
3

3-5
PRE-OPERATION INSPECTION AND MAINTENANCE
PRE-OPERATION INSPECTION AND MAINTENANCE
Before riding for break-in operation, practice or a race, make sure the machine is in good operating condition.
Before using this machine, check the following points.
GENERAL INSPECTION AND MAINTENANCE
Item Routine Page
CoolantCheck that coolant is filled up to the radiator cap. Check the cool-
ing system for leakage.P. 3-6 – 7
FuelCheck that a fresh mixture of oil and gasoline is filled in the fuel
tank. Check the fuel line for leakage.P. 1-12
Transmission oilCheck that the oil level is correct. Check the crankcase for leak-
age.P. 3-8 – 9
Gear shifter and clutchCheck that gears can be shifted correctly in order and that the
clutch operates smoothly.P. 3-7
Throttle grip/HousingCheck that the throttle grip operation and free play are correctly
adjusted. Lubricate the throttle grip and housing, if necessary.P. 3-7 – 8
Brakes Check the play of front brake and effect of front and rear brake. P. 3-9 – 12
Drive chainCheck drive chain slack and alignment. Check that the drive chain
is lubricated properly.P. 3-12 – 13
WheelsCheck for excessive wear and tire pressure. Check for loose
spokes and have no excessive play.P. 3-16
SteeringCheck that the handlebar can be turned smoothly and have no ex-
cessive play.P. 3-17
Front forks and rear shock
absorberCheck that they operate smoothly and there is no oil leakage.
P. 3-13 – 16
Cables (wires)Check that the clutch and throttle cables move smoothly. Check
that they are not caught when the handlebars are turned or when
the front forks travel up and down.—
Muffler Check that the muffler is tightly mounted and has no cracks. P. 4-3 – 4
Rear wheel sprocket Check that the rear wheel sprocket tightening bolt is not loose. P. 3-12
Lubrication Check for smooth operation. Lubricate if necessary. P. 3-18
Bolts and nuts Check the chassis and engine for loose bolts and nuts. P. 1-13
Lead connectorsCheck that the CDI magneto, CDI unit, and ignition coil are con-
nected tightly.P. 1-7
SettingsIs the machine set suitably for the condition of the racing course
and weather or by taking into account the results of test runs be-
fore racing? Are inspection and maintenance completely done?P. 7-1 – 11

3-6
ENGINE
ENGINE
CHECKING THE COOLANT LEVEL
Do not remove the radiator cap
"1", drain bolt and hoses when the
engine and radiator are hot. Scald-
ing hot fluid and steam may be
blown out under pressure, which
could cause serious injury. When
the engine has cooled, place a
thick towel over the radiator cap,
slowly rotate the cap counter-
clockwise to the detent. This pro-
cedure allows any residual
pressure to escape. When the
hissing sound has stopped, press
down on the cap while turning
counterclockwise and remove it.
Hard water or salt water is harmful
to the engine parts. You may use
distilled water, if you can't get soft
water.
1. Place the machine on a level
place, and hold it in an upright po-
sition.
2. Remove:
• Radiator cap
3. Check:
• Coolant level "a"
Coolant level low→Add coolant.
1. Radiator
CHANGING THE COOLANT
Do not remove the radiator cap
when the engine is hot.
Take care so that coolant does not
splash on painted surfaces. If it
splashes, wash it away with water.
1. Place a container under the en-
gine.
2. Remove:
• Coolant drain bolt "1"
3. Remove:
• Radiator cap
Drain the coolant completely.
4. Clean:
• Cooling system
Thoroughly flush the cooling sys-
tem with clean tap water.
5. Install:
• Copper washer
• Coolant drain bolt
6. Fill:
• Radiator
•Engine
To specified level.
• Do not mix more than one type of
ethylene glycol antifreeze con-
taining corrosion inhibitors for
aluminum engine.
• Do not use water containing im-
purities or oil.
Handling notes of coolant:
The coolant is harmful so it should be
handled with special care.
• When coolant splashes to your
eye.
Thoroughly wash your eye with
water and see your doctor.
• When coolant splashes to your
clothes.
Quickly wash it away with water
and then with soap.
• When coolant is swallowed.
Quickly make him vomit and take
him to a doctor.
7. Install:
• Radiator cap
Start the engine and warm it up
for a several minutes.
8. Check:
• Coolant level
Coolant level low→Add coolant.
CHECKING THE RADIATOR CAP
1. Inspect:
• Seal (radiator cap) "1"
• Valve and valve seat "2"
Crack/damage→Replace.
Exist fur deposits "3" →Clean or
replace.
CHECKING THE RADIATOR CAP
OPENING PRESSURE
1. Attach:
• Radiator cap tester "1" and adapt-
er "2"
Apply water on the radiator cap seal.
Coolant drain bolt:
10 Nm (1.0 m•kg, 7.2
ft•lb)
Recommended coolant:
High quality ethylene
glycol anti-freeze con-
taining anti-corrosion
for aluminum engine
Coolant "1" and water
(soft water) "2" mixing ra-
tio:
50%/50%
Coolant capacity:
0.9 L (0.79 Imp qt, 0.95
US qt)
Radiator cap tester:
YU-24460-01/90890-
01325
Radiator cap tester
adapter:
YU-33984/90890-01352

3-7
ENGINE
3. Radiator cap
2. Apply the specified pressure.
3. Inspect:
• Pressure
Impossible to maintain the speci-
fied pressure for 10 seconds→
Replace.
CHECKING THE COOLING
SYSTEM
1. Inspect:
• Coolant level
2. Attach:
• Radiator cap tester "1" and adapt-
er "2"
3. Apply the specified pressure.
• Do not apply pressure more than
specified pressure.
• Radiator should be filled fully.
4. Inspect:
• Pressure
Impossible to maintain the speci-
fied pressure for 10 seconds→
Repair.
•Radiator "1"
• Radiator hose joint "2"
Coolant leakage→Repair or re-
place.
• Radiator hose "3"
Swelling→Replace.ADJUSTING THE CLUTCH CABLE
FREE PLAY
1. Check:
• Clutch lever free play "a"
Out of specification→Adjust.
2. Adjust:
• Clutch lever free play
Clutch lever free play adjustment
steps:
a. Loosen the locknuts "1".
b. Turn the adjuster "2" until free
play "a" is within the specified lim-
its.
c. Tighten the locknuts.
• Before adjustment, expose the ad-
juster by moving the boot "3" and
cap "4" away.
• Make minute adjustment on the le-
ver side using the adjuster "5".
• After adjustment, check proper op-
eration of clutch lever.
3. Install:
• Cap "1"
•Boot "2"
Place the tip "a" of the cap in the boot.
ADJUSTING THE THROTTLE
CABLE FREE PLAY
1. Check:
• Throttle grip free play "a"
Out of specification→Adjust.
2. Adjust:
• Throttle grip free play
Throttle grip free play adjustment
steps:
a. Slide the adjuster cover.
b. Loosen the locknut "1".
c. Turn the adjuster "2" until the
specified free play is obtained.
d. Tighten the locknut.
Before adjusting the throttle cable
free play, the engine idle speed
should be adjusted.
After adjusting the throttle cable
free play, start the engine and turn
the handlebar to right and left and
make sure that the engine idling
does not run faster.
Radiator cap opening
pressure:
95–125 kPa (0.95–1.25
kg/cm
2, 13.5–17.8 psi)
Radiator cap tester:
YU-24460-01/90890-
01325
Radiator cap tester
adapter:
YU-33984/90890-01352
Standard pressure:
180 kPa (1.8 kg/cm
2,
25.6 psi)
Clutch lever free play "a"
:
8–13 mm (0.31–0.51 in)
Locknut:
4 Nm (0.4 m•kg, 2.9
ft•lb)Throttle grip free play
"a":
3–5 mm (0.12–0.20 in)
Locknut:
7 Nm (0.7 m•kg, 5.1
ft•lb)

4-5
RADIATOR
RADIATOR
REMOVING THE RADIATOR
Order Part name Q'ty Remarks
Drain the coolant.Refer to "CHANGING THE COOLANT" sec-
tion in the CHAPTER 3.
Seat and fuel tankRefer to "SEAT, FUEL TANK AND SIDE
COVERS" section.
1 Radiator guard 2
2 Radiator hose clamp (radiator hose 1, 3) 2 Only loosening.
3 Radiator hose 2 1
4 Left radiator 1
5 Radiator hose 4 1
6 Right radiator 1
7 Radiator hose 1 1
8 Radiator hose 3 1
9 Radiator breather hose 1
10 Nm (1.0 m kg, 7.2 ft lb)
2 Nm (0.2 m kg, 1.4 ft lb)
10 Nm (1.0 m kg, 7.2 ft lb)
10 Nm (1.0 m kg, 7.2 ft lb)
2 Nm (0.2 m kg, 1.4 ft lb)

4-6
RADIATOR
HANDLING NOTE
Do not remove the radiator cap
when the engine and radiator are
hot. Scalding hot fluid and steam
may be blown out under pressure,
which could cause serious injury.
When the engine has cooled, open
the radiator cap by the following
procedure:
Place a thick rag, like a towel, over
the radiator cap, slowly rotate the
cap counterclockwise to the de-
tent. This procedure allows any re-
sidual pressure to escape. When
the hissing sound has stopped,
press down on the cap while turn-
ing counterclockwise and remove
it.
CHECKING THE RADIATOR
1. Inspect:
• Radiator core "1"
Obstruction→Blow out with com-
pressed air through rear of the ra-
diator.
Bent fin→Repair/replace.
INSTALLING THE RADIATOR
1. Install:
• Radiator breather hose "1"
• Radiator hose 3 "2"
• Radiator hose 1 "3"
To right radiator "4".
Clamp the radiator hose in the direc-
tion as shown.
2. Install:
• Right radiator "1"
• Washer "2"
• Bolt (right radiator) "3"
• Radiator hose 4 "4"
Refer to "CABLE ROUTING DIA-
GRAM" section in the CHAPTER
2.
3. Install:
• Left radiator "1"
• Washer "2"
• Bolt (left radiator) "3"
• Radiator hose 2 "4"
Refer to "CABLE ROUTING DIA-
GRAM" section in the CHAPTER
2.
4. Tighten:
• Radiator hose clamp 1, 3 "5"
5. Install:
• Radiator guard "1"
• Bolt (radiator guard) "2"
Fit the hook "a" on the inner side first
into the radiator.
Radiator hose 3:
2 Nm (0.2 m•kg, 1.4
ft•lb)
Radiator hose 1:
2 Nm (0.2 m•kg, 1.4
ft•lb)
Bolt (right radiator):
10 Nm (1.0 m•kg, 7.2
ft•lb)
Radiator hose 4:
2 Nm (0.2 m•kg, 1.4
ft•lb)
Bolt (left radiator):
10 Nm (1.0 m•kg, 7.2
ft•lb)
Radiator hose 2:
2 Nm (0.2 m•kg, 1.4
ft•lb)
Radiator hose clamp 1, 3:
2 Nm (0.2 m•kg, 1.4
ft•lb)
Bolt (radiator guard):
10 Nm (1.0 m•kg, 7.2
ft•lb)

4-12
CYLINDER HEAD, CYLINDER AND PISTON
CYLINDER HEAD, CYLINDER AND PISTON
REMOVING THE CYLINDER HEAD AND CYLINDER
Order Part name Q'ty Remarks
Seat and fuel tank Refer to "SEAT, FUEL TANK AND SIDE
COVERS" section.
Exhaust pipe and silencerRefer to "EXHAUST PIPE AND SILENCER"
section.
Radiator Refer to "RADIATOR" section.
1 Spark plug 1
2 Engine bracket 2
3 Nut (cylinder head) 5Loosen each nut 1/4 turn, and remove them
after all nuts are loosened.
4 Cylinder head 1
5 Power valve housing 1
6 Push rod 1 Refer to removal section.
7 Nut (cylinder) 4
8 Cylinder 1
5 Nm (0.5 m kg, 3.6 ft lb)
4 Nm (0.4 m kg, 2.9 ft lb)
13 Nm (1.3 m kg, 9.4 ft lb)
28 Nm (2.8 m kg, 20 ft lb)
20 Nm (2.0 m kg, 14 ft lb)
30 Nm (3.0 m kg, 22 ft lb)
34 Nm (3.4 m kg, 24 ft lb)

4-23
KICK SHAFT AND SHIFT SHAFT
KICK SHAFT AND SHIFT SHAFT
REMOVING THE PRIMARY DRIVE GEAR
Order Part name Q'ty Remarks
Drain the transmission oil. Refer to "CHANGING THE TRANSMISSION
OIL" section in the CHAPTER 3.
Clutch cable Disconnect at engine side.
Bolt (brake pedal) Shift the brake pedal downward.
Radiator hose 4 Disconnect at water pump side.
Bolt (push rod)Refer to "CYLINDER HEAD, CYLINDER
AND PISTON" section.
1 Kickstarter crank 1
2 Crankcase cover (right) 1
3 Bolt (Primary drive gear) 1 Only loosening. Refer to removal section.
4 Primary driven gear 1 Refer to "CLUTCH" section.
5 Primary drive gear 1

4-33
CDI MAGNETO
CDI MAGNETO
REMOVING THE CDI MAGNETO
Order Part name Q'ty Remarks
Seat and fuel tankRefer to "SEAT, FUEL TANK AND SIDE
COVERS" section.
Bolt (Radiator) Refer to "RADIATOR" section.
Disconnect the CDI magneto lead.
1 Left crankcase cover 1
2 Nut (rotor) 1 Refer to removal section.
3 Rotor 1 Refer to removal section.
4 Stator 1
5 Woodruff key 1

4-35
ENGINE REMOVAL
ENGINE REMOVAL
REMOVING THE ENGINE
Order Part name Q'ty Remarks
Hold the machine by placing the suitable stand
under the engine.Refer to "HANDLING NOTE".
Seat and fuel tank Refer to "SEAT, FUEL TANK AND SIDE
COVERS" section.
Carburetor Refer to "CARBURETOR AND REED
VALVE" section.
Exhaust pipe and silencer Refer to "EXHAUST PIPE AND SILENCER"
section.
Clutch cable Disconnect at the engine side.
Radiator Refer to "RADIATOR" section.
Spark plug cap
Disconnect the CDI magneto lead.
1 Drive chain sprocket cover 1
2 Nut (drive sprocket) 1 Refer to removal section.
3 Lock washer 1 Refer to removal section.
4 Drive sprocket 1 Refer to removal section.
5Clip 1
6 Bolt (brake pedal) 1
26 Nm (2.6 m kg, 19 ft lb)
64 Nm (6.4 m kg, 46 ft lb)
64 Nm (6.4 m kg, 46 ft lb)
85 Nm (8.5 m kg, 61 ft lb)
75 Nm (7.5 m kg, 54 ft lb)
5 Nm (0.5 m kg, 3.6 ft lb)
34 Nm (3.4 m kg, 24 ft lb)