crankcase YAMAHA YZ125LC 2005 Owners Manual

CHAPTER 4
ENGINE
SEAT, FUEL TANK AND SIDE
COVERS.....................................................4-1
EXHAUST PIPE AND SILENCER..............4-3
RADIATOR..................................................4-4
CARBURETOR AND REED VALVE...........4-7
CYLINDER HEAD , CYLINDER AND
PISTON.....................................................4-17
CLUTCH AND PRIMARY DRIVEN
GEAR.......................................................4-30
KICK AXLE, SHIFT SHAFT AND
PRIMARY DRIVE GEAR...........................4-37
YPVS GOVERNOR...................................4-45
WATER PUMP..........................................4-48
CDI MAGNETO.........................................4-52
ENGINE REMOVAL..................................4-56
CRANKCASE AND CRANKSHAFT.........4-61
TRANSMISSION, SHIFT CAM AND
SHIFT FORK.............................................4-69
CHAPTER 5
CHASSIS
FRONT WHEEL AND REAR WHEEL........5-1
FRONT BRAKE AND REAR BRAKE.......5-10
FRONT FORK...........................................5-26
HANDLEBAR............................................5-41
STEERING................................................5-48
SWINGARM..............................................5-53
REAR SHOCK ABSORBER.....................5-61
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1-3
GEN
INFO
IMPORTANT INFORMATION
EC130000
IMPORTANT INFORMATION
EC131010
PREPARATION FOR REMOVAL AND
DISASSEMBLY
1. Remove all dirt, mud, dust, and foreign ma-
terial before removal and disassembly.
When washing the machine with high pres-
sured water, cover the parts as follows.
9Silencer exhaust port
9Side cover air intake port
9Crankcase cover hole at the bottom
9Water pump housing hole at the bottom
9End of each hose
2. Use proper tools and cleaning equipment.
Refer to “SPECIAL TOOLS” section.
3. When disassembling the machine, keep
mated parts together. They include gears,
cylinders, pistons, and other mated parts
that have been “mated” through normal
wear. Mated parts must be reused as an as-
sembly or replaced.
4. During the machine disassembly, clean all
parts and place them in trays in the order of
disassembly. This will speed up assembly
time and help assure that all parts are cor-
rectly reinstalled.
5. Keep away from fire.
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1-7
GEN
INFO
SPECIAL TOOLS
EC140002
SPECIAL TOOLS
The proper special tools are necessary for complete and accurate tune-up and assembly. Using the
correct special tool will help prevent damage caused by the use of improper tools or improvised tech-
niques. The shape and part number used for the special tool differ by country, so two types are provid-
ed. Refer to the list provided to avoid errors when placing an order.
NOTE:
9For U.S.A. and Canada, use part number starting with “YM-”, “YU-” or “ACC-”.
9For others, use part number starting with “90890-”.
Part number Tool name / How to use IIIustration
YU-1135-A, 90890-01135Crankcase separating toolYU-1135-A 90890-01135
These tool is used to split the crankcase as well
as remove the crankshaft from either case.
YM-1189, 90890-01189 Flywheel puller
YM-1189 90890-01189
This tool is used to remove the flywheel magneto.
YU-1235, 90890-01235 Rotor holding tool
YU-1235 90890-01235
This tool is used when loosening or tightening the
flywheel magneto securing nut.
YU-3097, 90890-01252 Dial gauge and stand
YU-3097 90890-01252
YU-1256 Spark plug hole dial standYU-1256
These tools are used to set the ignition timing.
Crankcase installing tool
YU-90050 90890-01274
YU-90050, 90890-01274 PotYU-90063 90890-01275
YU-90050, 90890-01275 BoltYM-0149990890-01278
YU-90063, 90890-01278 Adapter90890-01499
YM-01499, 90890-01499 Adapter
These tools are used to install the crankshaft.
YU-1304, 90890-01304 Piston pin puller
YU-1304 90890-01304
This tool is used to remove the piston pin.
YM-1312-A, 90890-01312Fuel level gaugeYM-1312-A 90890-01312
YM-01470, 90890-01470 Fuel level gauge adaptorYM-01470 90890-01470
This gauge is used to measure the fuel level in the
float chamber.
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1-8
GEN
INFO
SPECIAL TOOLS
Part number Tool name / How to use IIIustration
YU-24460-01, 90890-01325Radiator cap testerYU-24460-01 90890-01325
YU-33984, 90890-01352 AdapterYU-33984 90890-01352
These tools are used for checking the cooling
system.
YU-33270-B, 90890-01362Flywheel puller
YU-33270-B 90890-01362
These tool is used to split the crankcase.
YU-33975, 90890-01403 Ring nut wrench
YU-33975 90890-01403
This tool is used when tighten the steering ring nut
to specification.
YM-01442, 90890-01442 Fork seal driver
YM-01442 90890-01442
This tool is used when install the fork oil seal.
YM-01500, 90890-01500 Cap bolt wrench
YM-01500 90890-01500
This tool is used to loosen or tighten the base valve.
YM-01501, 90890-01501 Cap bolt ring wrench
YM-01501 90890-01501
This tool is used to loosen or tighten the damper
assembly.
YU-3112-C, 90890-03112 Yamaha pocket tester
YU-3112-C 90890-03112
Use this tool to inspect the coil resistance,
output voltage and amperage.
YM-91042, 90890-04086 Clutch holding tool
YM-91042 90890-04086
This tool is used to hold the clutch when removing
or installing the clutch boss securing nut.
YM-34487 Dynamic spark tester
YM-34487 90890-06754
90890-06754 Ignition checker
This instrument is necessary for checking the igni-
tion system components.
ACC-QUICK-GS-KT Quick gasket
®ACC-QUICK-GS-KT 90890-85505
90890-85505 YAMAHA Bond No. 1215
This sealant (Bond) is used for crankcase mating
surface, etc.
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2-5
SPECMAINTENANCE SPECIFICATIONS
Part to be tightened Thread size Q'tyT ightening torqueNm m•kg ft•lb
Spark plug
M14S×1.25 1 20 2.0 14
Cylinder head (nut) M 8 ×1.25 5 28 2.8 20
(stud) M 8 ×1.25 5 13 1.3 9.4
Cylinder (nut) M 8 ×1.25 4 30 3.0 22
(stud) M10 ×1.25 4 13 1.3 9.4
Power valve:
Cover M 5 ×0.8 4 5 0.5 3.6
Link lever M 4 ×0.7 1 4 0.4 2.9
Holder (power valve) M 5 ×0.8 4 8 0.8 5.8
Push rod M 5 ×0.8 1 5 0.5 3.6
Thrust plate M 5 ×0.8 1 4 0.4 2.9
Governor fork M 4 ×0.7 2 5 0.5 3.6
Housing M 5 ×0.8 3 4 0.4 2.9
Water pump housing cover M 6 ×1.0 4 10 1.0 7.2
Coolant drain bolt M 6 ×1.0 1 10 1.0 7.2
Radiator M 6 ×1.0 6 10 1.0 7.2
Radiator panel M 6 ×1.0 2 10 1.0 7.2
Radiator hose clamp M 6 ×1.0 8 1 0.1 0.7
Air filter element M 6 ×1.0 1 2 0.2 1.4
Carburetor joint M 6 ×1.0 4 10 1.0 7.2
Carburetor joint clamp M 4 ×0.7 1 2 0.2 1.4
Air filter joint clamp M 4 ×0.7 1 2 0.2 1.4
Air filter case M 6 ×1.0 4 8 0.8 5.8
Air filter guide clamp M 5 ×0.8 1 4 0.4 2.9
Read valve M 3 ×0.5 6 1 0.1 0.7
Throttle cable adjust bolt and locknut M 8 ×1.25 1 7 0.7 5.1
Throttle cable M 6 ×0.75 1 4 0.4 2.9
Crankcase M 6 ×1.0 12 14 1.4 10
Crankcase cover (right) M 6 ×1.0 8 10 1.0 7.2
Crankcase cover (left) M 6 ×1.0 4 5 0.5 3.6
Chain cover M 6 ×1.0 2 5 0.5 3.6
Bearing plate cover M 6 ×1.0 4 10 1.0 7.2
Holder M 6 ×1.0 1 10 1.0 7.2
Oil check bolt M 6 ×1.0 1 10 1.0 7.2
Oil drain bolt M10 ×1.25 1 20 2.0 14
Kick starter M 6 ×1.0 1 10 1.0 7.2
Cluch cover M 6 ×1.0 6 10 1.0 7.2
Primary drive gear M 8 ×1.25 1 48 4.8 35
Clutch boss M16 ×1.0 1 80 8.0 58
Clutch spring M 6 ×1.0 5 10 1.0 7.2
Clutch cable adjust bolt and locknut M 6 ×0.75 1 4 0.4 2.9
Drive sprocket M18 ×1.0 1 75 7.5 54
Shift pedal M 6 ×1.0 1 12 1.2 8.7
Bearing plate cover (shift cam) M 6 ×1.0 2 10 1.0 7.2
Shift guide M 6 ×1.0 2 10 1.0 7.2
Stopper lever M 6 ×1.0 1 10 1.0 7.2
Segment M 8 ×1.25 1 30 3.0 22
 
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2-13
SPECCABLE ROUTING DIAGRAM
EC240000
CABLE ROUTING DIAGRAM
1Ground lead
2High tension cord
3Grommet
4Air vent hose
5Crankcase breather hose
6Y.P.V.S. breather hose
7Throttle cable
8Clutch cable
9Engine bracket (right)
0Engine bracket (left)
qAir vent hose (left)
wAir vent hose (right)
e“ENGINE STOP” button leadAPass the clutch cable on the
outside of the throttle cable and
“ENGINE STOP” button lead.
BInsert the tip of the fuel tank
breather hose into the hole in
the steering shaft cap.
CAlign the throttle cable locating
tape with the cable guide.
DPass through the cable guide
the throttle cable, “ENGINE
STOP” button lead and clutch
cable.
EPass the throttle cable and
clutch cable above the radiator
hose, and pass the “ENGINE
STOP” button lead below the
radiator hose.FInstall the ignition coil, side
core and ground lead together
to the frame.
GClamp the clutch cable to the
left engine bracket. Clamp the
clutch cable below the position-
ing grommet.
HPass the air vent hose back of
the throttle cable.
IPass the air vent hose, over-
flow hose and crankcase
breather hose between the
frame and connecting rod.
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2-14
SPECCABLE ROUTING DIAGRAM
JPass the radiator breather hose
and Y.P.V.S. breather hose
from the outside of the engine
bracket to the inside of the
downtube.
KClamp the C.D.I. magneto lead,
radiator breather hose and
Y.P.V.S. breather hose.
LClamp to the frame the C.D.I.
magneto lead and radiator
breather hose.
MPass the air vent hose, over-
flow hose and crankcase
breather hose so that they do
not contact the rear shock
absorber.
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3-4
PRE-OPERATION INSPECTION AND MAINTENANCE
INSP
ADJ
EC320000
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.
EC321000
GENERAL INSPECTION AND MAINTENANCE
Item Routine Page
Coolant Check that coolant is filled up to the radiator filler cap.
Check the cooling system for leakage.P3-5~9
Fuel Check that a fresh mixture of oil and gasoline is filled in
the fuel tank. Check the fuel line for leakage.P1-12
Transmission oil Check that the oil level is correct. Check the crankcase
for leakage.P3-12~14
Gear shifter and clutch Check that gears can be shifted correctly in order and
that the clutch operates smoothly.P3-9
Throttle grip/Housing Check that the throttle grip operation and free play
are correctly adjusted. Lubricate the throttle grip and P3-10~11
housing, if necessary.
Brakes Check the play of front brake and effect of front and
rear brake.P3-17~23
Chain Check chain slack and alignment. Check that the chain
is lubricated properly.P3-24~26
Wheels Check for excessive wear and tire pressure. Check for
loose spokes and have no excessive play.P3-34~35
Steering Check that the handlebar can be turned smoothly and
have no excessive play.P3-35~36
Front forks and Check that they operate smoothly and there is no oil
rear shock absorber leakage.P3-26~33
Cables (wires) Check that the clutch and throttle cables move smooth-
ly. 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.P3-15~16
Sprocket Check that the driven sprocket tightening bolt is
not loose.P3-24
Lubrication Check for smooth operation. Lubricate if necessary. P3-37
Bolts and nuts Check the chassis and engine for loose bolts and nuts. P1-16
Lead connectors Check that the CDI magneto, CDI unit, and ignition coil
are connected tightly.P1-6
Settings Is the machine set suitably for the condition of the
racing course and weather or by taking into account the
P7-1~23
results of test runs before racing? Are inspection and
maintenance completely done?
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3-39
IGNITION TIMING CHECK
INSP
ADJ
EC372012
IGNITION TIMING CHECK
1. Remove:
9Fuel tank
Refer to “SEAT, FUEL TANK AND SIDE
COVERS” section in the CHAPTER 4.
9Spark plug
9Crankcase cover (left)
2. Attach:
9Dial gauge 1
9Spark plug hole dial stand 2
3. Rotate the magneto rotor 1until the
piston reaches top dead center (TDC).
When this happens, the needle on the dial
gauge will stop and reverse directions even
though the rotor is being turned in the same
direction.
4. Set the dial gauge to zero at TDC.
5. From TDC, rotate the rotor clockwise
until the dial gauge indicates that the
piston is at a specified distance from TDC.
6. Check:
9Ignition timing
Punch mark aon rotor should be aligned
with punch mark bon stator.
Not aligned Adjust.
Dial gauge:
YU-3097/90890-01252
Spark plug hole dial stand:
YU-1256
Ignition timing (B.T.D.C.):
0.48 mm (0.019 in)
1C3-9-30-3B 17/5/04 1:22 PM Page 42

4-19
ENGCYLINDER HEAD, CYLINDER AND PISTON
EC473000
REMOVAL POINTSEC473210
Push rod
1. Remove:
9Bolt (push rod) 1
9Push rod 2
NOTE:
Set the collar 3included in owner’s tool kit to
remove the bolt (push rod).
EC473402
Piston and piston ring
1. Remove:
9Piston pin clip 1
NOTE:
Before removing the piston pin clip, cover the
crankcase with a clean rag to prevent the pis-
ton pin clip from falling into the crankcase cav-
ity.
2. Remove:
9Piston pin 1
9Piston 2
9Small end bearing 3
NOTE:
Before removing the piston pin, deburr the clip
groove and pin hole area. If the piston pin
groove is deburred and piston pin is still difficult
to remove, use the piston pin puller 4.
cC
Do not use a hammer to drive the piston
pin out.
3. Remove:
9Piston ring 1
NOTE:
Take care not to scratch the piston or damage
the piston ring by expanding it more than neces-
sary.
Piston pin puller:
YU-1304/90890-01304
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