YAMAHA YZ250F 2010 Owners Manual

4-27
CYLINDER AND PISTON
2. Position:• Piston ring(in cylinder)
Insert a ring into the cylinder and
push it approximately 10 mm (0.39 in)
into the cylinder. Push the ring with
the piston crown so that the ring will
be at a right angle to the cylinder
bore.
a. 10 mm (0.39 in)
3. Measure:
• Ring end gapOut of specification →Replace.
You cannot measure the end gap on
the expander spacer of the oil control
ring. If the oil control ring rails show
excessive gap, replace all three rings.
CHECKING THE PISTON PIN
1. Inspect:
• Piston pinBlue discoloration/grooves →Re-
place, then inspect the lubrication
system.
2. Measure:
• Piston pin-to-piston clearance
Measurement steps:
a. Measure the outside diameter (piston pin) "a".
If out of specification, replace the
piston pin. b. Measure the inside diameter (pis-
ton) "b".
c. Calculate the piston pin-to-piston clearance with the following for-
mula.
d. If out of specific ation, replace the
piston.
INSTALLING THE PISTON RING
AND PISTON
1. Install: •Piston ring
Onto the piston.
• Be sure to install the piston rings so that the manufacturer's marks or
numbers are located on the upper
side of the rings.
• Lubricate the piston and piston rings liberally with engine oil.
2. Position:
•Top ring
•2nd ring
•Oil ringOffset the piston ring end gaps as
shown.
a. Top ring end
b. 2nd ring end
c. Oil ring end (upper)
d. Oil ring
e. Oil ring end (lower)
3. Install: • Piston "1"
• Piston pin "2"
• Piston pin clip "3"
• Apply engine oil onto the piston pin and piston.
• Be sure that the arrow mark "a" on
the piston points to the exhaust side
of the engine.
• Before installing the piston pin clip,
cover the crankcase with a clean
rag to prevent the piston pin clip
from falling into the crankcase.
• Install the piston pin clips with their ends facing downward.
End gap:
Standard <Limit>
Top
ring 0.15–0.25 mm
(0.006–0.010 in) 0.50
mm
(0.020 in)
2nd
ring 0.30–0.45 mm
(0.012–0.018 in) 0.80
mm
(0.031 in)
Oil
ring 0.10–0.40 mm
(0.004–0.016 in) —
Outside diameter (piston
pin): 15.991–16.000 mm
(0.6296–0.6299 in)
Inside diameter (piston):
16.002–16.013 mm
(0.6300–0.6304 in)
Piston pin-to-pis ton clearance =
Inside diameter (piston) "b" -
Outside diameter (piston pin)
"a"
Piston pin-to-piston
clearance:0.002–0.022 mm
(0.0001–0.0009 in)
<Limit>:0.07 mm (0.003
in)
New

4-28
CYLINDER AND PISTON
INSTALLING THE CYLINDER
1. Lubricate:•Piston
• Piston ring
• Cylinder
Apply a liberal coating of engine oil.
2. Install:
• Dowel pin "1"
• O-ring "2"
Apply the lithium soap base grease
on the O-ring.
3. Install:• Cylinder gasket "1"
• Cylinder "2"
Install the cylinder with one hand
while compressing the piston rings
with the other hand.
• Pass the timing chain "3" through the timing chain cavity.
• Be careful not to damage the tim-
ing chain guide "4" during instal-
lation.
4. Install:• Bolt (cylinder) "5"
Bolt (cylinder):10 Nm (1.0 m•kg, 7.2
ft•lb)

4-29
CLUTCH
CLUTCH
REMOVING THE CLUTCHOrder Part name Q'ty Remarks Drain the engine oil. Refer to "CHANGING THE ENGINE OIL"
section in the CHAPTER 3.
Brake pedal Refer to "ENGINE REMOVAL" section.
Clutch cable Disconnect at engine side.
1 Clutch cover 1
2 Clutch spring 5
3 Pressure plate 1
4 Push rod 1 1
5 Circlip 1
6 Washer 1
7 Bearing 1
8Ball 1
9 Push rod 2 1
10 Friction plate 9
11 Clutch plate 8
12 Nut (clutch boss) 1 Refer to removal section.
13 Lock washer 1 Refer to removal section.

4-30
CLUTCH
14 Clutch boss1 Refer to removal section.
15 Thrust washer 1
16 Primary driven gear 1
17 Spacer 1
18 Washer 1
19 Push lever shaft 1
Order
Part name Q'tyRemarks

4-31
CLUTCH
REMOVING THE CLUTCH BOSS
1. Remove:•Nut "1"
• Lock washer "2"
• Clutch boss "3"
Straighten the lock washer tab and
use the clutch holding tool "4" to hold
the clutch boss.
A. For USA and CDN
B. Except for USA and CDN
CHECKING THE CLUTCH
HOUSING AND BOSS
1. Inspect: • Clutch housing "1"
Cracks/wear/damage →Replace.
• Clutch boss "2" Scoring/wear/damage →Replace.
CHECKING THE PRIMARY DRIVEN
GEAR
1. Check: • Circumferential play
Free play exists →Replace.
• Gear teeth "a" Wear/damage →Replace. CHECKING THE CLUTCH
SPRINGS
1. Measure:
• Clutch spring free length "a"
Out of specification →Replace
springs as a set.
CHECKING THE FRICTION
PLATES
1. Measure: • Friction plate thickness
Out of specification →Replace
friction plate as a set.
Measure at all four points.
CHECKING THE CLUTCH PLATES
1. Measure: • Clutch plate warpageOut of specification →Replace
clutch plate as a set.
Use a surface plate "1" and thick-
ness gauge "2". CHECKING THE PUSH LEVER
SHAFT
1. Inspect:
• Push lever shaft "1"
Wear/damage →Replace.
CHECKING THE PUSH ROD
1. Inspect: • Push rod 1 "1"
• Bearing "2"
• Washer "3"
• Push rod 2 "4"
•Ball "5"Wear/damage/bend →Replace.
INSTALLING THE PUSH LEVER
SHAFT
1. Install: • Push lever shaft "1"
• Bolt (push lever shaft) "2"
• Apply the lithium soap base grease
on the oil seal lip.
• Apply the engine oil on the push le- ver shaft.
• Fit the seat plate "3" in the groove "a" of the push lever shaft and tight-
en the bolt (seat plate).
Clutch holding tool: YM-91042/90890-04086
Clutch spring free
length:
35.7 mm (1.41 in)
<Limit>: 34.7 mm (1.37
in)
Friction plate thickness: 2.9–3.1 mm
(0.114–0.122 in)
<Limit>: 2.8 mm (0.110
in)
Warp limit: 0.1 mm (0.004 in)
Bolt (push lever shaft): 10 Nm (1.0 m•kg, 7.2
ft•lb)

4-32
CLUTCH
INSTALLING THE CLUTCH
1. Install:• Washer "1"
• Spacer "2"
• Primary driven gear "3"
• Thrust washer "4"
• Clutch boss "5"
Apply the engine oil on the primary
driven gear inner circumference.
2. Install:• Lock washer "1"
• Nut (clutch boss) "2"
Use the clutch holding tool "3" to hold
the clutch boss.
A. For USA and CDN
B. Except for USA and CDN
3. Bend the lock washer "1" tab. 4. Install:
• Friction plate "1"
• Clutch plate 1 "2"
• Install the clutch plates and friction plates alternately on the clutch
boss, starting with a friction plate
and ending with a friction plate.
• Apply the engine oil on the friction
plates and clutch plates.
5. Install:•Bearing "1"
• Washer "2"
• Circlip "3" To push rod 1 "4".
Apply the engine oil on the bearing
and washer.
6. Install:
• Push rod 2 "1"
• Ball "2"
• Push rod 1 "3"
Apply the engine oil on the push rod
1, 2 and ball.
7. Install:• Pressure plate "1" 8. Install:
• Clutch spring "1"
• Bolt (clutch spring) "2"
Tighten the bolts in stage, using a
crisscross pattern.
9. Install:• Dowel pin "1"
• Gasket (clutch cover) "2"
10. Install: • Clutch cover "1"
• Bolt (clutch cover)
Tighten the bolts in stage, using a
crisscross pattern.
Nut (clutch boss): 75 Nm (7.5 m•kg, 54
ft•lb)
Clutch holding tool: YM-91042/90890-04086
Bolt (clutch spring):10 Nm (1.0 m•kg, 7.2
ft•lb)
Bolt (clutch cover): 10 Nm (1.0 m•kg, 7.2
ft•lb)

4-33
OIL FILTER ELEMENT AND WATER PUMP
OIL FILTER ELEMENT AND WATER PUMP
REMOVING THE OIL FILTER ELEMENT AND WATER PUMPOrder Part name Q'ty Remarks Drain the engine oil. Refer to "CHANGING THE ENGINE OIL"
section in the CHAPTER 3.
Drain the coolant. Refer to "CHANGING
THE COOLANT" sec-
tion in the CHAPTER 3.
Radiator hose 3 Disconnect at water pump side.
Exhaust pipe Refer to "EXHAUST PIPE AND SILENCER"
section.
Brake pedal Refer to "ENGINE REMOVAL" section.
Right engine guard
1 Oil filter element cover 1
2 Oil filter element 1
3 Water pump housing 1
4 Oil delivery pipe 1
5 Bolt (oil hose) 1
6 Kickstarter crank 1
7 Right crankcase cover 1
8 Impeller 1 Refer to removal section.

4-34
OIL FILTER ELEMENT AND WATER PUMP
9 Washer1 Refer to removal section.
10 Impeller shaft 1 Refer to removal section.
11 Oil seal 2 Refer to removal section.
12 Bearing 1 Refer to removal section.
Order
Part name Q'tyRemarks

4-35
OIL FILTER ELEMENT AND WATER PUMP
REMOVING THE IMPELLER
SHAFT
1. Remove:• Impeller "1"
• Washer "2"
• Impeller shaft "3"
Hold the impeller shaft on its width
across the flats "a" with spanners,
etc. and remove the impeller.
REMOVING THE OIL SEAL
It is not necessary to disassemble the
water pump, unless there is an abnor-
mality such as excessive change in
coolant level, discoloration of coolant,
or milky transmission oil.
1. Remove:• Bearing "1"
2. Remove: • Oil seal "1" CHECKING THE OIL DELIVERY
PIPE
1. Inspect:
• Oil delivery pipe "1"
Bend/damage →Replace.
Clogged →Blow.
CHECKING THE IMPELLER SHAFT
1. Inspect: • Impeller shaft "1"Bend/wear/damage →Replace.
Fur deposits →Clean.
CHECKING THE IMPELLER SHAFT
GEAR
1. Inspect: • Gear teeth "a"Wear/damage →Replace.
CHECKING THE BEARING
1. Inspect: •BearingRotate inner race with a finger.
Rough spot/seizure →Replace. CHECKING THE OIL SEAL
1. Inspect:
• Oil seal "1"Wear/damage →Replace.
INSTALLING THE OIL SEAL
1. Install: • Oil seal "1"
• Apply the lithium soap base grease on the oil seal lip.
• Install the oil seal with its manufac- ture's marks or numbers facing the
right crankcase cover "2".
2. Install:• Bearing "1"
Install the bearing by pressing its out-
er race parallel.

4-36
OIL FILTER ELEMENT AND WATER PUMP
INSTALLING THE IMPELLER
SHAFT
1. Install:• Impeller shaft "1"
• Washer "2"
• Impeller "3"
• Take care so that the oil seal lip is not damaged or the spring does not
slip off its position.
• When installing the impeller shaft, apply the lithium soap base grease
on the oil seal lip and impeller shaft.
And install the shaft while turning it.
• Hold the impeller shaft on its width across the flats "a" with spanners,
etc. and install the impeller.
INSTALLING THE RIGHT
CRANKCASE COVER
1. Install:• Dowel pin "1"
• O-ring "2"
•Collar "3"
• Gasket "4"
Apply the lithium soap base grease
on the O-ring.
2. Install:
• Right crankcase cover "1"
• Bolt (right crankcase cover) "2"
• Apply the engine oil on the impeller shaft end.
• Mesh the impeller shaft gear "3" with primary drive gear "4".
• Tighten the bolts in stage, using a
crisscross pattern.
INSTALLING THE KICKSTARTER
CRANK
1. Install:• Kickstarter crank "1"
• Washer
• Bolt (kickstarter crank)
Install so that the clearance "a" be-
tween the kickstarter crank and en-
gine bracket mounting bolt is 8 mm
(0.31 in) or more and that the kick-
starter crank does not contact the
right crankcase cover when it is
pulled out.
2. Install:
• Oil hose "1"
• Bolt (oil hose) "2"
3. Install: • Copper washer "1"
• Oil delivery pipe "2"
• Union bolt (M8) "3"
• Union bolt (M10) "4"
First tighten the union bolts temporar-
ily. Then retighten them with the width
"a" across flats of the oil delivery pipe
held tight with a spanner.
Impeller: 14 Nm (1.4 m•kg, 10
ft•lb)
Bolt (right crankcase
cover):
10 Nm (1.0 m•kg, 7.2
ft•lb)
Bolt (kickstarter crank): 33 Nm (3.3 m•kg, 24
ft•lb)Bolt (oil hose): 8 Nm (0.8 m•kg, 5.8
ft•lb)
Union bolt (M8): 18 Nm (1.8 m•kg, 13
ft•lb)
Union bolt (M10): 20 Nm (2.0 m•kg, 14
ft•lb)