2008 YAMAHA YZ250F Owners Manual

3-11
ENGINE
ADJUSTING THE VALVE
CLEARANCE
•The valve clearance should be ad-
justed when the engine is cool to
the touch.
• The piston must be at Top Dead Center (T.D.C.) on compression
stroke to check or adjust the valve
clearance.
1. Remove:• Seat
• Fuel tankRefer to "SEAT, FUEL TANK
AND SIDE COVERS" section in
the CHAPTER 4.
2. Remove: • Spark plug
• Cylinder head coverRefer to "CAMSHAFTS" section
in the CHAPTER 4.
3. Remove:
• Timing mark accessing screw "1"
• Crankshaft end accessing screw "2"
• O-ring
4. Check: • Valve clearance
Out of specification
→Adjust.
Checking steps:
a. Turn the crankshaft counterclock- wise with a wrench.
b. Align the T.D.C. mark "a" on the rotor with the align mark "b" on the
crankcase cover when piston is at
T.D.C. on compression stroke.
In order to be sure that the piston is at
Top Dead Center, the punch mark "c"
on the exhaust camshaft and the
punch mark "d" on the intake cam-
shaft must align with the cylinder
head surface, as shown in the illustra-
tion.
c. Measure the valve clearance "e"
using a feeler gauge "1".
Record the measured reading if the
clearance is incorrect.
5. Adjust:• Valve clearance
Adjustment steps:
a. Remove the camshaft (intake and exhaust).
Refer to "CAMSHAFTS" section
in the CHAPTER 4.
b. Remove the valve lifters "1" and the pads "2".
•Place a rag in the timing chain
space to prevent pads from falling
into the crankcase.
• Identity each valve lifter and pad
position very carefully so that they
can be reinstalled in their original
place.
c. Select the proper pad using the pad selecting table.
The thickness "a" of each pad is indi-
cated in hundredths of millimeters on
the pad upper surface.
d. Round off the last digit of the in-stalled pad number to the nearest
increment.
EXAMPLE:
Installed pad number = 148
Rounded off value = 150
Pads can only be selected in 0.05
mm increments.
e. Locate the rounded-off value and the measured valve clearance in
the chart "PAD SELECTION TA-
BLE". The field where these two
coordinates intersect shows the
new pad number to use.
Valve clearance (cold):
Intake valve:0.10–0.15 mm
(0.0039–0.0059 in)
Exhaust valve: 0.17–0.22 mm
(0.0067–0.0087 in)
Pad range Pad Availabili-
ty: 25 incre-
ments
No.
120– No.
240 1.20
mm– 2.40 mm Pads are avail-
able in 0.05 mm increments
Last digit of pad number Rounded valve
0, 1 or 2 0
4, 5 or 6 5
8 or 9 10

3-12
ENGINE
Use the new pad number only as a
guide when verifying the valve clear-
ance adjustment.
f. Install the new pads "3" and the valve lifters "4".
•Apply the engine oil on the valve lift-
ers.
• Apply the molybdenum disulfide oil on the valve stem ends.
• Valve lifter must turn smoothly
when rotated with a finger.
• Be careful to reinstall valve lifters and pads in their original place.
g. Install the camshafts (exhaust
and intake).
Refer to "CAMSHAFTS" section
in the CHAPTER 4.

3-13
ENGINE
INTAKE
EXHAUST

3-14
CHASSIS
CHASSIS
BLEEDING THE HYDRAULIC
BRAKE SYSTEM
Bleed the brake system if:
• The system has been disassem-bled.
• A brake hose has been loosened or removed.
• The brake fluid is very low.
• The brake operation is faulty.
A dangerous loss of braking per-
formance may occur if the brake
system is not properly bled.
1. Remove: • Brake master cylinder cap
• Diaphragm
• Reservoir float (front brake)
• Protector (rear brake)
2. Bleed: • Brake fluid
Air bleeding steps:
a. Add proper brake fluid to the res-
ervoir.
b. Install the diaphragm. Be careful
not to spill any fluid or allow the
reservoir to overflow.
c. Connect the clear plastic tube "2"
tightly to the caliper bleed screw
"1".
A. Front
B. Rear
d. Place the other end of the tube into a container.
e. Slowly apply the brake lever or pedal several times.
f. Pull the lever in or push down on
the pedal. Hold the lever or pedal
in position.
g. Loosen the bleed screw and allow
the lever or pedal to travel to-
wards its limit.
h. Tighten the bleed screw when the
lever or pedal limit has been reached; then release the lever or
pedal.
i. Repeat steps (e) to (h) until of the air bubbles have been removed
from the system.
If bleeding is difficult, it may be nec-
essary to let the brake fluid system
stabilize for a few hours. Repeat the
bleeding procedure when the tiny
bubbles in the system have disap-
peared.
j. Add brake fluid to the level line on
the reservoir.
Check the operation of the brake
after bleeding the brake system.
3. Install:• Protector (rear brake)
• Reservoir float (front brake)
• Diaphragm
• Brake master cylinder cap
ADJUSTING THE FRONT BRAKE
1. Check: • Brake lever position "a"
2. Remove: • Brake lever cover
3. Adjust: • Brake lever position
Brake lever position adjustment
steps:
a. Loosen the locknut "1".
b. Turn the adjusting bolt "2" until the lever position "a" is within speci-
fied position. c. Tighten the locknut.
Be sure to tighten the locknut, as it
will cause poor brake perfor-
mance.
4. Install:
• Brake lever cover
ADJUSTING THE REAR BRAKE
1. Check: • Brake pedal height "a"Out of specification
→Adjust.
2. Adjust: • Brake pedal height
Pedal height adjustment steps:
a. Loosen the locknut "1".
b. Turn the adjusting nut "2" until the pedal height "a" is within specified
height.
c. Tighten the locknut.
• Adjust the pedal height between the maximum "A" and the mini-
mum "B" as shown. (In this ad-
justment, the bolt "3" end "b"
should protrude out of the
threaded portion "4" but not be
less than 2 mm (0.08 in) "c" away
from the brake pedal "5").
• After the pedal height adjust-
ment, make sure that the rear
brake does not drag.
Bleed screw: 6 Nm (0.6 m•kg, 4.3
ft•lb)
Brake lever position "a":
Standard posi- tion Extent of ad-
justment
95 mm (3.74 in) 86–105 mm
(3.39–4.13 in)
Locknut: 5 Nm (0.5 m •kg, 3.6
ft•lb)
Brake pedal height "a": 5 mm (0.20 in)

3-15
CHASSIS
CHECKING AND REPLACING THE
FRONT BRAKE PADS
1. Inspect:• Brake pad thickness "a"Out of specification
→Replace as
a set.
2. Replace: •Brake pad
Brake pad replacement steps:
a. Remove the pad pin plug "1".
b. Loosen the pad pin "2".
c. Remove the brake caliper "3" from the front fork.
d. Remove the pad pin and brake pads "4". e. Connect the transparent hose "5"
to the bleed screw "6" and place
the suitable container under its
end.
f. Loosen the bleed screw and push the brake caliper piston in.
Do not reuse the drained brake flu-
id.
g. Tighten the bleed screw.
h. Install the brake pads "7" and pad
pin.
ŒInstall the brake pads with their pro-
jections "a" into the brake caliper re-
cesses "b".
• Temporarily tighten the pad pin at this point.
i. Install the brake caliper "8" and
tighten the pad pin "9". j. Install the pad pin plug "10".
3. Inspect:
• Brake fluid levelRefer to "CHECKING THE
BRAKE FLUID LEVEL" section.
4. Check: • Brake lever operationA softy or spongy feeling
→Bleed
brake system.
Refer to "BLEEDING THE HY-
DRAULIC BRAKE SYSTEM" sec-
tion.
CHECKING AND REPLACING THE
REAR BRAKE PADS
1. Inspect: • Brake pad thickness "a"
Out of specification
→Replace as
a set.
2. Replace: • Brake pad
Brake pad replacement steps:
a. Remove the protector "1" and pad pin plug "2".
Brake pad thickness:
4.4 mm (0.17 in)
: 1.0 mm (0.04
in)
Bleed screw:6 Nm (0.6 m•kg, 4.3
ft•lb)
Bolt (brake caliper): 28 Nm (2.8 m•kg, 20
ft•lb)
Pad pin: 18 Nm (1.8 m•kg, 13
ft•lb)
Pad pin plug:3 Nm (0.3 m•kg, 2.2
ft•lb)
Brake pad thickness: 6.4 mm (0.25 in)
: 1.0 mm (0.04
in)

3-16
CHASSIS
b. Loosen the pad pin "3".
c. Remove the rear wheel "4" and brake caliper "5".
Refer to "FRONT WHEEL AND
REAR WHEEL" section in the
CHAPTER 5.
d. Remove the pad pin "6" and brake pads "7".
e. Connect the transparent hose "8" to the bleed screw "9" and place
the suitable container under its
end.
f. Loosen the bleed screw and push the brake caliper piston in.
Do not reuse the drained brake flu-
id.
g. Tighten the bleed screw.
h. Install the brake pad "10" and pad pin "11".
• Install the brake pads with their pro-jections "a" into the brake caliper re-
cesses "b".
• Temporarily tighten the pad pin at this point.
i. Install the brake caliper "12" and
rear wheel "13".
Refer to "FRONT WHEEL AND
REAR WHEEL" section in the
CHAPTER 5.
j. Tighten the pad pin "14".
k. Install the pad pin plug "15" and
protector "16".
3. Inspect:• Brake fluid levelRefer to "CHECKING THE
BRAKE FLUID LEVEL" section.
4. Check: • Brake pedal operationA softy or spongy feeling
→Bleed
brake system.
Refer to "BLEEDING THE HY-
DRAULIC BRAKE SYSTEM" sec-
tion.
CHECKING THE REAR BRAKE
PAD INSULATOR
1. Remove: •Brake pad
Refer to "CHECKING AND RE-
PLACING THE REAR BRAKE PADS" section.
2. Inspect: • Rear brake pad insulator "1"Damage
→Replace.
CHECKING THE BRAKE FLUID
LEVEL
1. Place the brake master cylinder so that its top is in a horizontal po-
sition.
2. Inspect:
• Brake fluid levelFluid at lower level
→Fill up.
• Use only designated quality brake fluid to avoid poor brake
performance.
• Refill with same type and brand of brake fluid; mixing fluids
could result in poor brake perfor-
mance.
• Be sure that water or other con- taminants do not enter master
cylinder when refilling.
• Clean up spilled fluid immediate- ly to avoid erosion of painted
surfaces or plastic parts.
a. Lower level
A. Front
B. Rear
CHECKING THE SPROCKET
1. Inspect: • Sprocket teeth "a"Excessive wear
→Replace.
Replace the drive sprocket, rear
wheel sprocket and drive chain as a
set.
Bleed screw:
6 Nm (0.6 m•kg, 4.3
ft•lb)
Pad pin:18 Nm (1.8 m•kg, 13
ft•lb)
Pad pin plug: 3 Nm (0.3 m•kg, 2.2
ft•lb)
Bolt (protector): 7 Nm (0.7 m•kg, 5.1
ft•lb)
Recommended brake flu-
id:DOT #4

3-17
CHASSIS
CHECKING THE DRIVE CHAIN
1. Measure:• Drive chain length (15 links) "a"Out of specification
→Replace.
• While measuring the drive chain
length, push down on the drive
chain to increase its tension.
• Measure the length between drive
chain roller "1" and "16" as shown.
• Perform this measurement at two or three different places.
2. Remove:
• Master link clip
•Joint "1"
• Drive chain "2"
3. Clean: • Drive chain
Place it in kerosene, and brush off
as much dirt as possible. Then re-
move the drive chain from the ker-
osene and dry the drive chain.
4. Check: • Drive chain stiffness "a"
Clean and oil the drive chain and hold as illustrated.
Stiff
→Replace the drive chain.
5. Install: • Drive chain "1"
• Joint "2"
• Master link clip "3"
Be sure to install the master link
clip to the direction as shown.
a. Turning direction
6. Lubricate: • Drive chain
ADJUSTING THE DRIVE CHAIN
SLACK
1. Elevate the rear wheel by placing the suitable stand under the en-
gine.
2. Check:
• Drive chain slack "a"Above the seal guard installation
bolt.
Out of specification
→Adjust.
Before checking and/or adjusting, ro-
tate the rear wheel through several
revolutions and check the slack sev-
eral times to find the tightest point.
Check and/or adjust the drive chain
slack with the rear wheel in this "tight chain" position.
3. Adjust:
• Drive chain slack
Drive chain slack adjustment
steps:
a. Loosen the axle nut "1" and lock- nuts "2".
b. Adjust the drive chain slack by
turning the adjusters "3".
c. Turn each adjuster exactly the same amount to maintain correct
axle alignment. (There are marks
"a" on each side of the drive chain
puller alignment.)
Turn the adjuster so that the drive
chain is in line with the sprocket, as
viewed from the rear.
Too small drive chain slack will
overload the engine and other vital
parts; keep the slack within the
specified limits.
d. Tighten the axle nut while pushing down the drive chain.
e. Tighten the locknuts.
Drive chain length (15
links): : 242.9 mm
(9.563 in)
Drive chain lubricant:SAE 10W-30 motor oil
or suitable chain lubri-
cants
Drive chain slack: 48–58 mm (1.9–2.3 in)
To tighten→Turn the adjuster "3"
counterclockwise.
To loosen
→Turn the adjuster "3"
clockwise and push wheel for-
ward.
Axle nut:125 Nm (12.5 m•kg, 90
ft•lb)
Locknut: 19 Nm (1.9 m•kg, 13
ft•lb)

3-18
CHASSIS
CHECKING THE FRONT FORK
1. Inspect:• Front fork smooth actionOperate the front brake and
stroke the front fork.
Unsmooth action/oil leakage
→
Repair or replace.
CLEANING THE FRONT FORK OIL
SEAL AND DUST SEAL
1. Remove: •Protector
• Dust seal "1"
Use a thin screw driver, and be care-
ful not to damage the inner fork tube
and dust seal.
2. Clean:• Dust seal "a"
•Oil seal "b"
•Clean the dust seal and oil seal af-
ter every run.
• Apply the lithium soap base grease
on the inner tube.
RELIEVING THE FRONT FORK
INTERNAL PRESSURE
If the front fork initial movement feels
stiff during a run, relieve the front fork
internal pressure.
1. Elevate the front wheel by placing a suitable stand under the engine.
2. Remove the air bleed screw "1" and release the internal pressure
from the front fork.
3. Install: • Air bleed screw
ADJUSTING THE FRONT FORK
REBOUND DAMPING FORCE
1. Adjust: • Rebound damping force
By turning the adjuster "1".
• STANDARD POSITION: This is the position which is back
by the specific number of clicks
from the fully turned-in position.
Do not force the adjuster past the
minimum or maximum extent of
adjustment. The adjuster may be
damaged.
Always adjust each front fork to
the same setting. Uneven adjust-
ment can cause poor handling and
loss of stability.
ADJUSTING THE FRONT FORK
COMPRESSION DAMPING FORCE
1. Adjust:• Compression damping force
By turning the adjuster "1".
• STANDARD POSITION: This is the position which is back
by the specific number of clicks
from the fully turned-in position.
Do not force the adjuster past the
minimum or maximum extent of
adjustment. The adjuster may be
damaged.
Always adjust each front fork to
the same setting. Uneven adjust-
ment can cause poor handling and
loss of stability.
CHECKING THE REAR SHOCK
ABSORBER
1. Inspect:• Swingarm smooth action
Abnormal noise/unsmooth action
→Grease the pivoting points or
repair the pivoting points.
Damage/oil leakage
→Replace.
Air bleed screw:
1 Nm (0.1 m•kg, 0.7
ft•lb)
Stiffer "a"
→Increase the re-
bound damping force. (Turn
the adjuster "1" in.)
Softer "b"
→Decrease the re-
bound damping force. (Turn
the adjuster "1" out.)
Extent of adjustment:
Maximum Minimum
Fully turned in
position 20 clicks out
(from maximum
position)
Standard position: 11 clicks out
* 10 clicks out
* For EUROPE
Stiffer "a" →Increase the com-
pression damping force. (Turn
the adjuster "1" in.)
Softer "b"
→Decrease the com-
pression damping force. (Turn
the adjuster "1" out.)
Extent of adjustment:
Maximum Minimum
Fully turned in
position 20 clicks out
(from maximum
position)
Standard position: 9 clicks out
* 10 clicks out
* For EUROPE