2002 YAMAHA YZ250LC engine

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)
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4-30
CYLINDER HEAD, CYLINDER AND PISTONENG
EC475382
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
.
35 Nm (3.5 m•kg, 25 ft•lb)
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4-32
CYLINDER HEAD, CYLINDER AND PISTONENG
9. Install:
9Spark plug 1
9Spark plug cap 2
8. Install:
9Engine bracket 1
9Bolt (engine bracket) 2
9Engine mounting bolt (upper) 3
20 Nm (2.0 m•kg, 14 ft•lb)
34 Nm (3.4 m•kg, 24 ft•lb)
69 Nm (6.9 m•kg, 50 ft•lb)
5NX-9-30-4B 6/7/01 1:56 PM Page 10

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)
5NX-9-30-4B 6/7/01 1:56 PM Page 12

34 Nm (3.4 m•kg, 24 ft•lb)
4-60
ENGINE REMOVALENG
Extent of removal Order Part name Q’ty Remarks
ENGINE REMOVAL
Preparation for
Hold the machine by placing the
removalsuitable stand under the engine.
Seat and fuel tankRefer to “SEAT, FUEL TANK AND
SIDE COVERS” section.
Carburetor and carburetor jointRefer to “CARBURETOR AND REED
VALVE” section.
Exhaust pipe and silencer Refer to “EXHAUST PIPE AND
Exhaust pipe stay (rear) SILENCER” section.
Clutch cable Disconnect at engine side.
Radiator Refer to “RADIATOR” section.
Spark plug
Disconnect the CDI magneto lead.
CDI unit
Reservoir tank (rear brake) Refer to “FRONT BRAKE AND REAR
BRAKE” section in the CHAPTER 5.
EC4M0000
ENGINE REMOVAL
w
Support the machine securely so there is no dan-
ger of it falling over.



26 Nm (2.6 m•kg, 19 ft•lb)
69 Nm (6.9 m•kg, 50 ft•lb)
69 Nm (6.9 m•kg, 50 ft•lb)
75 Nm (7.5 m•kg, 54 ft•lb)
8 Nm (0.8 m•kg, 5.8 ft•lb)
85 Nm (8.5 m•kg, 61 ft•lb)
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4-61
ENGINE REMOVALENG
Extent of removal:1Engine removal
Extent of removal Order Part name Q’ty Remarks
1 Chain cover 1
2 Nut (drive sprocket) 1
3 Lock washer 1 Refer to “REMOVAL POINTS”.
4 Drive sprocket 1
5 Clip 1
6 Bolt (brake pedal) 1
7 Brake pedal 1
8 Engine bracket 2
9 Engine mounting bolt 3
10 Pivot shaft 1 Remove completely.
11 Engine 1 Refer to “REMOVAL POINTS”.
1





26 Nm (2.6 m•kg, 19 ft•lb)
69 Nm (6.9 m•kg, 50 ft•lb)
34 Nm (3.4 m•kg, 24 ft•lb)
69 Nm (6.9 m•kg, 50 ft•lb)
75 Nm (7.5 m•kg, 54 ft•lb)
8 Nm (0.8 m•kg, 5.8 ft•lb)
85 Nm (8.5 m•kg, 61 ft•lb)
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4-62
ENGINE REMOVALENG
EC4M3340
Engine removal
NOTE:
Make sure that the couplers, hoses and cables
are disconnected.
1. Lift the engine 1up to the point where the
engine’s mounting front does not contact the
bracket on the frame.
2. Remove the engine 1aslant and upward
while inclining it toward the kick crank side
so that the engine’s mounting top does not
contact the bracket on the frame.
EC4M3000
REMOVAL POINTS
EC4F3100
Drive sprocket
1. Remove:
9Nut (drive sprocket) 1
9Lock washer 2
NOTE:
9Straighten the lock washer tab.
9Loosen the nut while applying the rear brake.
2. Remove:
9Drive sprocket 1
9Drive chain 2
NOTE:
Remove the drive sprocket together with the
drive chain.
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4-63
ENGINE REMOVALENG
EC4M5341
Drive sprocket
1. Install:
9Drive sprocket 1
9Drive chain 2
NOTE:
Install the drive sprocket together with the drive
chain.
EC4M5211
Brake pedal
1. Install:
9Spring 1
9Brake pedal 2
9O-ring 3
9Bolt (brake pedal) 4
9Clip 5
NOTE:
9Apply the lithium soap base grease on the bolt,
O-rings and brake pedal bracket.
9Install the clip with its stopper portion afacing
inward.
EC4M5000
ASSEMBLY AND INSTALLATIONEC4M5123
Engine installation
1. Install:
9Engine 1
Install the engine from right side.
9Pivot shaft 2
9Engine mounting bolt (lower) 3
9Engine mounting bolt (front) 4
9Engine bracket 5
9Bolt (engine bracket) 6
9Engine mounting bolt (upper) 7
NOTE:
Apply the molybdenum disulfide grease on the
pivot shaft.
85 Nm (8.5 m•kg, 61 ft•lb)
69 Nm (6.9 m•kg, 50 ft•lb)
69 Nm (6.9 m•kg, 50 ft•lb)
34 Nm (3.4 m•kg, 24 ft•lb)
69 Nm (6.9 m•kg, 50 ft•lb)
26 Nm (2.6 m•kg, 19 ft•lb)
5NX-9-30-4C 6/5/01 4:25 PM Page 28