engine oil YAMAHA YZ250LC 2003 Owner's Manual

4-29
CYLINDER HEAD, CYLINDER AND PISTONENG
7. Install:
9O-ring 1
9Side holder 2
9Screw (side holder) 3
9YPVS breather hose 4
NOTE:
9Apply the lithium soap base grease on the O-
rings.
9Install the side holder with its projection a
facing upward.
8. Install:
9Gasket (power valve cover) 1
9Power valve cover 2
9Screw (power valve cover) 3
NOTE:
9Install the gasket with its cut afacing down-
ward and the seal print side toward the power
valve cover.
9Install the power valve cover so that the arrow
mark bfaces upward.
EC475233
Piston ring and piston
1. Install:
9Piston ring 1
NOTE:
9Take care not to scratch the piston or damage
the piston ring.
9Align the piston ring gap with the pin 2.
9After installing the piston ring, check the
smooth movement of it.
2. Install:
9Gasket (cylinder) 1
9Small end bearing 2
9Dowel pin 3
NOTE:
9Apply the engine oil onto the bearing (crank-
shaft and connecting rod) and connecting rod
big end washers.
9Install the gasket with the seal print side toward
the crankcase.
4 Nm (0.4 m•kg, 2.9 ft•lb)
4 Nm (0.4 m•kg, 2.9 ft•lb)
5UP-9-30-4B 5/24/02 5:29 PM Page 4

4-30
CYLINDER HEAD, CYLINDER AND PISTONENG
EC475383
Cylinder head and cylinder
1. Apply:
9Engine oil
To piston 1piston ring 2and cylinder sur-
face.
2. Install:
9Cylinder 1
cC
Make sure the piston rings are properly
positioned. Install the cylinder with one
hand while compressing the piston rings
with the other hand.
NOTE:
After installing, check the smooth movement of
the piston.
3. Install:
9Nut (cylinder) 1
NOTE:
Tighten the nuts in stage, using a crisscross pat-
tern.
3. Install:
9Piston 1
9Piston pin 2
9Piston pin clip 3
NOTE:
9The arrow aon the piston dome must point to
exhaust side.
9Before installing the piston pin clip, cover the
crankcase with a clean rag to prevent the pis-
ton pin clip from falling into the crankcase cavi-
ty.
cC
Do not allow the clip open ends to meet the
piston pin slot b b
.
42 Nm (4.2 m•kg, 30 ft•lb)
5UP-9-30-4B 5/24/02 5:29 PM Page 6

4-33
CLUTCH AND PRIMARY DRIVEN GEARENG
Extent of removal Order Part name Q’ty Remarks
CLUTCH PLATE AND
FRICTION PLATE REMOVAL
Preparation for Drain the transmission oil.
Refer to “TRANSMISSION OIL REPLACE-
removalMENT“ section in the CHAPTER 3.
Bolt (brake pedal) Shift the brake pedal downward.
Rotor and stator Refer to
“CDI MAGNETO“section.
Clutch cable Disconnect at engine side.
1 Clutch cover 1
2 Screw (clutch spring) 6
3 Clutch spring 6
4 Pressure plate 1
5 Friction plate 8
6 Clutch plate 7
Extent of removal:1Clutch plate and friction plate removal
EC490000
CLUTCH AND PRIMARY DRIVEN GEAREC498000
CLUTCH PLATE AND FRICTION PLATE
1
10 Nm (1.0 m•kg, 7.2 ft•lb)
10 Nm (1.0 m•kg, 7.2 ft•lb)
5UP-9-30-4B 5/24/02 5:30 PM Page 12

4-65
CRANKCASE AND CRANKSHAFTENG
Extent of removal Order Part name Q’ty Remarks
CRANKCASE AND CRANKSHAFT
REMOVAL
Preparation for Engine Refer to “ENGINE REMOVAL”section.
removal Piston Refer to “
CYLINDER HEAD, CYLINDER
AND PISTON
” section.
Primary drive gear
Kick idle gearRefer to “
KICK AXLE, SHIFT SHAFT AND
Stopper leverPRIMARY DRIVE GEAR”section.
Rotor and stator Refer to “CDI MAGNETO” section.
1 Segment 1 Refer to “REMOVAL POINTS”.
2 Bolt [L=50 mm (1.97 in)] 7
3 Bolt [L=60 mm (2.36 in)] 1
4 Bolt [L=70 mm (2.76 in)] 3
5 Holder 2
6 Crankcase (right) 1 Use special tool.
7 Crankcase (left) 1 Refer to “REMOVAL POINTS”.
8 Crankshaft 1 Use special tool.
Refer to “REMOVAL POINTS”.
9 Oil seal 2
10 Bearing 2 Refer to “REMOVAL POINTS”.




EC4N0000
CRANKCASE AND CRANKSHAFT
12
3
Extent of removal:1Crankcase separation2Crankshaft removal
3Crankshaft bearing removal



10 Nm (1.0 m•kg, 7.2 ft•lb)30 Nm (3.0 m•kg, 22 ft•lb)
14 Nm (1.4 m•kg, 10 ft•lb)
10 Nm (1.0 m•kg, 7.2 ft•lb)
5UP-9-30-4C 5/24/02 5:33 PM Page 32

4-71
CRANKCASE AND CRANKSHAFTENG
8. Tighten:
9Segment 1
9Bolt (segment) 2
NOTE:
9When installing the segment onto the shift cam
3, align the punch mark awith the dowel pin
b.
9Turn the segment clockwise until it stops and
tighten the bolt.
30 Nm (3.0 m•kg, 22 ft•lb)
7. Install:
9Tension spring 1
9Holder 2
9Bolt (holder) 3
NOTE:
Install the holder so that it contacts the projec-
tion aon the crankcase (right).
10 Nm (1.0 m•kg, 7.2 ft•lb)
9. Remove:
9Sealant
Forced out on the cylinder mating surface.
10. Apply:
9Engine oil
To the crank pin, bearing, oil delivery hole
and connecting rod big end washer.
11. Check:
9Crankshaft and transmission operation
Unsmooth operation
Repair.
5UP-9-30-4C 5/24/02 5:33 PM Page 44

5-1
CHASFRONT WHEEL AND REAR WHEEL
Extent of removal Order Part name Q’ty Remarks
FRONT WHEEL REMOVAL
Preparation for
Hold the machine by placing the
removalsuitable stand under the engine.
1 Hose cover 1
2 Bolt (brake hose holder) 2 Only loosening.
3 Bolt (axle holder) 4 Only loosening.
4 Nut (front wheel axle) 1
5 Front wheel axle 1
6 Front wheel 1
7 Collar 2
8 Oil seal 2
9 Bearing 2 Refer to “REMOVAL POINTS”.
10 Brake disc 1
EC500000
CHASSISEC590000
FRONT WHEEL AND REAR WHEELEC598000
FRONT WHEEL
2
13
3
Extent of removal:1Front wheel removal2Wheel bearing removal3Brake disc removal
w
Support the machine securely so there is no dan-
ger of it falling over.
23 Nm (2.3 m•kg, 17 ft•lb)
23 Nm (2.3 m•kg, 17 ft•lb)
105 Nm (10.5 m•kg, 75 ft•lb)
16 Nm (1.6 m•kg, 11 ft•lb)
7 Nm (0.7 m•kg, 5.1 ft•lb)12 Nm (1.2 m•kg, 8.7 ft•lb)
10 Nm (1.0 m•kg, 7.2 ft•lb)
5UP-9-30-5AN 5/24/02 5:41 PM Page 2

5-2
CHASFRONT WHEEL AND REAR WHEEL
EC598100
REAR WHEEL
Extent of removal:1Rear wheel removal2Wheel bearing removal3Brake disc removal
Extent of removal Order Part name Q’ty Remarks
REAR WHEEL REMOVAL
Preparation for
Hold the machine by placing the
removalsuitable stand under the engine.
1 Nut (rear wheel axle) 1
2 Rear wheel axle 1
3 Chain puller 2
4 Rear wheel 1 Refer to “REMOVAL POINTS”.
5 Collar 2
6 Driven sprocket 1
7 Oil seal 2
8 Circlip 1
9 Bearing 2 Refer to “REMOVAL POINTS”.
10 Brake disc 1
2
13
3
w
Support the machine securely so there is no dan-
ger of it falling over.
125 Nm (12.5 m•kg, 90 ft•lb)
14 Nm (1.4 m•kg, 10 ft•lb)
16 Nm (1.6 m•kg, 11 ft•lb)
16 Nm (1.6 m•kg, 11 ft•lb)
42 Nm (4.2 m•kg, 30 ft•lb)
5UP-9-30-5AN 5/24/02 5:41 PM Page 4

6-1
ELECTRICAL COMPONENTS AND WIRING DIAGRAMELEC
EC600000
ELECTRICAL
EC610000
ELECTRICAL COMPONENTS AND WIRING DIAGRAM
EC611000
ELECTRICAL COMPONENTS
1CDI unit
2“ENGINE STOP” button
3Ignition coil
4TPS (throttle position sensor)
5Solenoid valve
6CDI magneto
7Spark plug
EC612000
WIRING DIAGRAM
COLOR CODE
B...................Black
L ...................Blue
O ..................Orange
R ..................Red
Y...................Yellow
B/L................Black/Blue
B/R ...............Black/Red
B/W ..............Black/White
G/L ..............Green/Blue
G/W ..............Green/White
W/L...............White/Blue
W/R ..............White/Red
L
Y
B/LYL
B/LY LL
Y
B
B/W
B B/W
B
R
BB
RR
RR
R
B
B/R
G/L
G/W
W/R
W/L W/L B/R
G/L
W/R
B G/W G/L B/R W/L
G/W B W/R
O
B G/W G/L
Y B/L
L
W/R
W/L
B
R
B/R
B/W
O G/L
B/L
L
W/L
B
R
B/R
B/WG/W
Y
W/R
OB/L
5UP-9-30-6 5/24/02 5:35 PM Page 2

6-2
IGNITION SYSTEMELEC
EC620000
IGNITION SYSTEM
EC621003
INSPECTION STEPS
Use the following steps for checking the possibility of the malfunctioning engine being attributable to
ignition system failure and for checking the spark plug which will not spark.
*Clean or replace
spark plug.
Primary coil
Secondary coil
Repair or replace.
Spark
Check entire ignition
system for connection.
Spark gap test
No good
No good
No good
No good
No good
No good No Spark
Check “ENGINE STOP”
button.
Pick-up coil
Source coil
Check ignition coil.
Check CDI magneto.
Replace CDI unit.
Replace.
Replace.
Replace.
Replace.
Replace.
*marked: Only when the ignition checker is used.
NOTE:
9Remove the following parts before inspection.
1) Seat
2) Fuel tank
9Use the following special tools in this inspection.
Dynamic spark tester:
YM-34487
Ignition checker:
90890-06754Pocket tester:
YU-3112-C/90890-03112
OK
OK
OK
OKReplace.
Check spark plug cap.No good
OK
5UP-9-30-6 5/24/02 5:35 PM Page 4

6-9
TPS (THROTTLE POSITION SENSOR) SYSTEMELEC
Check entire ignition
system for connection.Repair or replace.
OK
OKTPS coil
No goodReplace.Check TPS.
OKSource coil
No goodReplace.*Check CDI magneto.
TPS input
voltageNo goodReplace.Check CDI unit.
No good
EC690000
TPS (THROTTLE POSITION SENSOR) SYSTEM
EC691001
INSPECTION STEPS
If the TPS will not operate, use the following inspection steps.
*marked: Refer to “IGNITION SYSTEM” section.
NOTE:
9Remove the following parts before inspection.
1) Seat
2) Fuel tank
9Use the following special tools in this inspection.
Inductive tachometer:
YU-8036-B
Engine tachometer:
90890-03113Pocket tester:
YU-3112-C/90890-03112
5UP-9-30-6 5/24/02 5:36 PM Page 22