light YAMAHA WR 250F 2008 Owner's Guide

5-18
CAMSHAFTS
The camshafts should be installed
onto the cylinder head so that the
punch mark "c" on the exhaust cam-
shaft and the punch mark "d" on the
intake camshaft must align with the
cylinder head surface, as shown in
the illustration.
Do not turn the crankshaft during
the camshaft installation. Damage
or improper valve timing will re-
sult.
d. Install the clips, camshaft caps "4"
and bolts (camshaft cap) "5".
• Before removing the clips, cover the cylinder head with a clean rag to
prevent the clips from into the cylin-
der head cavity.
• Apply the molybdenum disulfide oil on the thread of the bolts (camshaft
cap).
• Tighten the bolts to the specified torque in two or three steps in the
proper tightening sequence as
shown.
The bolts (camshaft cap) must be
tightened evenly, or damage to the
cylinder head, camshaft caps, and
camshaft will result.
2. Install:• Timing chain tensioner
Installation steps:
a. While pressing the tensioner rod lightly with fingers, use a thin
screwdriver and wind the tension-
er rod up fully clockwise.
b. With the rod fully wound and the chain tensioner UP mark "a" fac-
ing upward, install the gasket "1"
and the timing chain tensioner "2",
and tighten the bolt "3" to the
specified torque.
c. Release the screwdriver, check the tensioner rod to come out and
tighten the gasket "4" and the cap
bolt "5" to the specified torque.
3. Turn:
• CrankshaftCounterclockwise several turns.
4. Check:
• Rotor T.D.C. markAlign with the crankcase align
mark.
• Camshaft match marks Align with the cylinder head sur-
face.
Out of alignment →Adjust. 5. Install:
• Timing mark accessing screw "1"
• Crankshaft end accessing screw "2"
6. Install: • Timing chain guide (top side) "1"
• Cylinder head cover gasket "2"
• Cylinder head cover "3"
• Bolt (cylinder head cover) "4"
Apply the sealant on the cylinder
head cover gasket.
7. Install:• Cylinder head breather hose
• Spark plug
Bolt (camshaft cap):
10 Nm (1.0 m•kg, 7.2
ft•lb)
Bolt (timing chain ten-
sioner):10 Nm (1.0 m•kg, 7.2
ft•lb)
Tensioner cap bolt: 7 Nm (0.7 m•kg, 5.1
ft•lb)
Bolt (cylinder head cov-
er): 10 Nm (1.0 m•kg, 7.2
ft•lb)
YAMAHA Bond No. 1215
(ThreeBond
® No. 1215):
90890-85505
Spark plug: 13 Nm (1.3 m•kg, 9.4
ft•lb)

5-23
VALVES AND VALVE SPRINGS
4. Measure:• Margin thickness "a"Out of specification →Replace.
5. Measure: • Runout (valve stem)Out of specification →Replace.
• When installing a new valve always
replace the guide.
• If the valve is removed or replaced
always replace the oil seal.
6. Eliminate:• Carbon deposits(from the valve face and valve
seat)
7. Inspect: • Valve seatPitting/wear →Reface the valve
seat.
8. Measure: • Valve seat width "a"
Out of specification →Reface the
valve seat.
Measurement steps:
a. Apply Mechanic's blueing dye (Dykem) "b" to the valve face.
b. Install the valve into the cylinder head.
c. Press the valve through the valve guide and onto the valve seat to
make a clear pattern.
d. Measure the valve seat width. Where the valve seat and valve
face made contact, blueing will
have been removed.
e. If the valve seat is too wide, too
narrow, or the seat is not cen-
tered, the valve se at must be re-
faced.
9. Lap: • Valve face
• Valve seat
After refacing the valve seat or re-
placing the valve and valve guide, the
valve seat and valve face should be
lapped.
Lapping steps:
a. Apply a coarse lapping compound
to the valve face.
Do not let the co mpound enter the
gap between the valve stem and
the guide.
b. Apply molybdenum disulfide oil to the valve stem. c. Install the valve into the cylinder
head.
d. Turn the valve until the valve face and valve seat are evenly pol-
ished, then clean off all of the
compound.
For best lapping results, lightly tap
the valve seat while rotating the valve
back and forth between your hands.
e. Apply a fine lapping compound to the valve face and repeat the
above steps.
After every lapping operation be sure
to clean off all of the compound from
the valve face and valve seat.
f. Apply Mechanic's blueing dye (Dykem) to the valve face.
g. Install the valve into the cylinder head.
h. Press the valve through the valve
guide and onto the valve seat to
make a clear pattern.
i. Measure the valve seat width
again. If the valve seat width is out
of specification, reface and relap
the valve seat.
CHECKING THE VALVE SPRINGS
1. Measure:• Valve spring free length "a"Out of specification →Replace.
Margin thickness:
Intake:
0.8 mm (0.0315 in)
Exhaust: 0.7 mm (0.0276 in)
Runout limit: 0.01 mm (0.0004 in)
Valve seat width: Intake:
0.9–1.1 mm (0.0354–
0.0433 in)
:1.6 mm
(0.0630 in)
Exhaust: 0.9–1.1 mm (0.0354–
0.0433 in)
:1.6 mm
(0.0630 in)
Free length (valve
spring): Intake:36.58 mm (1.44 in)
: 36.81 mm
(1.45 in)
Exhaust:
35.58 mm (1.40 in)
: 36.54 mm
(1.44 in)

5-24
VALVES AND VALVE SPRINGS
2. Measure:• Compressed spring force "a"
Out of specification →Replace.
b. Installed length
3. Measure: • Spring tilt "a"
Out of specification →Replace.
CHECKING THE VALVE LIFTERS
1. Inspect: • Valve lifterScratches/damage →Replace
both lifters and cylinder head. INSTALLING THE VALVES
1. Apply:
• Molybdenum disulfide oilOnto the valve stem and valve
stem seal.
2. Install: • Valve "1"
• Valve spring seat "2"
• Valve stem seal "3"
• Valve spring "4"
• Valve spring retainer "5"To cylinder head.
• Make sure that each valve is in-stalled in its original place, also re-
ferring to the painted color as
follows.
Intake (middle) "a": Orange
Intake (right/left) "b": Green
Exhaust "c": Purple
• Install the valve springs with the
larger pitch "d" facing upward.
e. Smaller pitch
3. Install:
• Valve cotter
While compressing the valve spring
with a valve spring compressor "1" in-
stall the valve cotters.
4. To secure the va lve cotters onto
the valve stem, lightly tap the
valve tip with a piece of wood.
Hitting the valve tip with excessive
force could damage the valve.
5. Install: • Adjusting pad "1"
• Valve lifter "2"
• Apply the molybdenum disulfide oil
on the valve stem end.
• Apply the engine oil on the valve lift- ers.
• Valve lifter must turn smoothly when rotated with a finger.
• Be careful to reinstall valve lifters and pads in their original place.
Compressed spring
force: Intake:
103–118 N at 29.13
mm (10.50–12.09 kg at
29.13 mm, 23.15–
26.66 lb at 1.15 in)
Exhaust: 126–144 N at 29.30
mm (12.85–14.68 kg at
29.30 mm, 28.32–
32.37 lb at 1.15 in)
Spring tilt limit: Intake:2.5°/1.6 mm (0.063 in)
Exhaust: 2.5°/1.6 mm (0.063 in)
Valve spring compres-
sor:
YM-4019/90890-04019

5-60
CRANKCASE AND CRANKSHAFT
DISASSEMBLING THE
CRANKCASE
1. Separate:• Right crankcase
• Left crankcase
Separation steps:
a. Remove the crankcase bolts "1", hose guide "2" and clutch cable
holder "3".
Loosen each bolt 1/4 of a turn at a
time and after all the bolts are loos-
ened, remove them.
b. Remove the right crankcase "4".
• Place the crankcase with its left
side downward and split it by insert-
ing a screwdriver tip into the split-
ting slit "a" in the crankcase.
• Lift the right crankcase horizontally while lightly patting the case split-
ting slit and engine mounting boss
using a soft hammer, and leave the
crankshaft and transmission with
the left crankcase.
Use soft hammer to tap on the
case half. Tap only on reinforced
portions of case. Do not tap on
gasket mating surface. Work slow-
ly and carefully. Make sure the
case halves separate evenly. If the
cases do not separate, check for a
remaining case bolt or fitting. Do
not force.
c. Remove the dowel pins and O-
ring.
REMOVING THE CRANKSHAFT
1. Remove:• Crankshaft "1"
Use the crankcase separating
tool "2".
Do not use a hammer to drive out
the crankshaft.
REMOVING THE CRANKCASE
BEARING
1. Remove:•Bearing "1"
• Remove the bearing from the crankcase by pressing its inner
race.
• Do not use the removed bearing.
CHECKING THE TIMING CHAIN
AND TIMING CHAIN GUIDE
1. Inspect: • Timing chain
Cracks/stiff →Replace the timing
chain and camshaft sprocket as a
set.
2. Inspect: • Timing chain guideWear/damage →Replace. CHECKING THE CRANKCASE
1. Inspect:
• Contacting surface "a"Scratches →Replace.
• Engine mounting boss "b", crank- case
Cracks/damage →Replace.
2. Inspect: • BearingRotate inner race with a finger.
Rough spot/seizure →Replace.
3. Inspect: • Oil sealDamage →Replace.
CHECKING THE CRANKSHAFT
1. Measure: • Runout limit "a"
• Small end free play limit "b"
• Connecting rod big end side clearance "c"
• Crank width "d" Out of specification →Replace.
Use the dial gauge and a thick-
ness gauge.
Crankcase separating
tool: YU-1135-A/90890-
01135
Dial gauge and stand: YU-3097/90890-01252
Standard
Runo
ut lim-
it: 0.03 mm (0.0012
in) 0.05
mm
(0.002 in)
Small
end
free
play: 0.4–1.0 mm
(0.016–0.039 in) 2.0 mm
(0.08 in)
Side
clear-
ance: 0.15–0.45 mm
(0.0059–0.0177 in) 0.50
mm
(0.02 in)
Crack
width: 55.95–56.00
mm (2.203–
2.205 in) —

5-62
CRANKCASE AND CRANKSHAFT
5. Install:• Dowel pin "1"
• O-ring "2"
• Right crankcaseTo left crankcase.
• Apply the lithium soap base grease
on the O-ring.
• Fit the right crankcase onto the left crankcase. Tap lightly on the case
with soft hammer.
• When installing the crankcase, the connecting rod should be posi-
tioned at TDC (top dead center).
6. Tighten:
• Hose guide "1"
• Clutch cable holder "2"
• Bolt (crankcase) "3"
Tighten the crankcase tightening
bolts in stage, using a crisscross pat-
tern.
7. Install:• Oil delivery pipe 2 "1"
• O-ring "2"
• Bolt (oil delivery pipe 2) "3"
Apply the lithium soap base grease
on the Orings.
8. Install:• Timing chain "1"
• Timing chain guide (intake side)
"2"
• Bolt (timing chain guide) "3"
9. Remove: • Sealant
Forced out on the cylinder mating
surface.
10. Apply:
• Engine oilTo the crank pin, bearing and oil
delivery hole.
11. Check: • Crankshaft and transmission op-eration.
Unsmooth operation →Repair.
Bolt (crankcase):
12 Nm (1.2 m•kg, 8.7
ft•lb)
Bolt (oil delivery pipe 2): 10 Nm (1.0 m•kg, 7.2
ft•lb)
Bolt (timing chain guide):10 Nm (1.0 m•kg, 7.2
ft•lb)

5-64
TRANSMISSION, SHIFT CAM AND SHIFT FORK
REMOVING THE TRANSMISSION
1. Remove:• Main axle "1"
• Drive axle "2"
• Shift cam
• Shift fork 3
• Shift fork 2
• Shift fork 1
• Remove assembly with the collar "3" installed to the crankcase.
• Remove assembly carefully. Note
the position of each part. Pay partic-
ular attention to the location and di-
rection of shift forks.
• Remove the main axle, drive axle, shift cam and shift fork all together
by tapping lightly on the transmis-
sion drive axle with a soft hammer.
CHECKING THE GEARS
1. Inspect:
• Matching dog "a"
• Gear teeth "b"
• Shift fork groove "c"Wear/damage →Replace.
2. Inspect: • O-ring "1"
Damage →Replace.
3. Check: • Gears movementUnsmooth movement →Repair or
replace.
CHECKING THE BEARING
1. Inspect: • Bearing "1"
Rotate inner race with a finger.
Rough spot/seizure →Replace. CHECKING THE SHIFT FORK,
SHIFT CAM AND SEGMENT
1. Inspect:
• Shift fork "1"Wear/damage/scratches →Re-
place.
2. Inspect: • Shift cam "1"
• Segment "2"Wear/damage →Replace.
3. Check: • Shift fork movement
Unsmooth operation →Replace
shift fork.
For a malfunctioning shift fork, re-
place not only the shift fork itself but
the two gears each adjacent to the
shift fork.
INSTALLING THE TRANSMISSION
1. Install:
• 5th pinion gear (19T) "1"
• 3rd pinion gear (17T) "2"
• Collar "3"
• 4th pinion gear (21T) "4"
• 2nd pinion gear (16T) "5"To main axle "6".
Apply the molybdenum disulfide oil
on the inner and end surface of the
idler gear and on the inner surface of
the sliding gear, then install.
2. Install:• 2nd wheel gear (28T) "1"
• 4th wheel gear (23T) "2"
• 3rd wheel gear (23T) "3"
• 5th wheel gear (17T) "4"
• 1st wheel gear (31T) "5"
• O-ring "6" To drive axle "7".
• Apply the molybdenum disulfide oil on the inner and end surface of the
idler gear and on the inner surface
of the sliding gear, then install.
• Apply the lithium soap base grease
on the O-ring.
3. Install:• Washer "1"
• Circlip "2"
• Be sure the circlip sharp-edged cor-ner "a" is positioned opposite side
to the washer and gear "b".
• Install the circlip with its ends "c" settled evenly on the spline crests.

6-13
FRONT BRAKE AND REAR BRAKE
2. Install:• Brake lever "1"
• Bolt (brake lever) "2"
• Nut (brake lever) "3"
Apply the silicone grease on the
brake lever sliding surface, bolt and
contacting surface of the brake mas-
ter cylinder piston.
INSTALLING THE REAR BRAKE
MASTER CYLINDER
1. Install:• Copper washer "1"
• Brake hose "2"
• Union bolt "3"
Always use new copper washers.
Install the brake hose so that its
pipe portion "a" directs as shown
and lightly touches the projection
"b" on the brake master cylinder.
2. Install:• Brake master cylinder "1"
• Bolt (brake master cylinder) "2"
3. Install: • Spring "1"
• Brake pedal "2"
• O-ring "3"
• Bolt (brake pedal) "4"
• Clip "5"
Apply the lithium soap base grease
on the bolt, O-ring and brake pedal
bracket.
4. Install:
•Pin "1"
• Washer "2"
• Cotter pin "3"
After installing, check the brake pedal
height. Refer to "ADJUSTING THE
REAR BRAKE" section in the CHAP-
TER 3.
INSTALLING THE FRONT BRAKE
HOSE
1. Install:• Copper washer "1"
• Brake hose "2"
• Union bolt "3"
Always use new copper washers.
Install the brake hose so that its
pipe portion "a" directs as shown
and lightly touches the projection
"b" on the brake caliper.
2. Install:
• Brake hose holder "1"
• Bolt (brake hose holder) "2"
Bolt (brake lever):
6 Nm (0.6 m•kg, 4.3
ft•lb)
Nut (brake lever): 6 Nm (0.6 m•kg, 4.3
ft•lb)
Union bolt: 30 Nm (3.0 m•kg, 22
ft•lb)
Bolt (brake master cylin-
der):10 Nm (1.0 m•kg, 7.2
ft•lb)
Bolt (brake pedal): 26 Nm (2.6 m•kg, 19
ft•lb)
Union bolt: 30 Nm (3.0 m•kg, 22
ft•lb)
Bolt (brake hose holder): 10 Nm (1.0 m•kg, 7.2
ft•lb)

6-14
FRONT BRAKE AND REAR BRAKE
3. Install:• Brake hose holder "1"
• Nut (brake hose holder) "2"
Align the top "a" of the brake hose
holder with the paint "b" of the brake
hose.
4. Pass the brake hose through the front brake hose guides "1".
5. Install: • Copper washer "1"
• Brake hose "2"
• Union bolt "3"
Always use new copper washers.
Install the brake hose so that it
contacts the brake master cylinder
projection "a" and that its bent
portion "b" faces downward.
INSTALLING THE REAR BRAKE
HOSE
1. Install:• Copper washer "1"
• Brake hose "2"
• Union bolt "3"
Always use new copper washers.
Install the brake hose so that its
pipe portion "a" directs as shown
and lightly touches the projection
"b" on the brake caliper.
2. Install:
• Brake hose holder "1"
• Screw (brake hose holder) "2"
After installing the brake hose
holders, make sure the brake hose
does not contact the spring (rear
shock absorber). If it does, correct
its twist.
FILLING THE BRAKE FLUID
1. Fill:• Brake fluidUntil the fluid level reaches
"LOWER" level line "a".
• Use only the designated quality brake fluid:
otherwise, the rubber seals may
deteriorate, causi ng leakage and
poor brake performance.
• Refill with the same type of brake fluid;
mixing fluids may result in a
harmful chemical reaction and
lead to poor performance.
• Be careful that water does not enter the master cylinder when
refilling. Water will significantly
lower the boiling point of the flu-
id and may result in vapor lock.
Brake fluid may erode painted sur-
faces or plastic parts. Always
clean up spilled fluid immediately.
A. Front
B. Rear
2. Air bleed: • Brake system
Refer to "BLEEDING THE HY-
DRAULIC BRAKE SYSTEM" sec-
tion in the CHAPTER 3.
Nut (brake hose holder):
7 Nm (0.7 m•kg, 5.1 ft
•lb)
Union bolt: 30 Nm (3.0 m•kg, 22
ft•lb)
Union bolt:30 Nm (3.0 m•kg, 22
ft•lb)
Screw (brake hose hold-
er): 2 Nm (0.2 m•kg, 1.4
ft•lb)
Recommended brake flu-
id: DOT #4

6-16
FRONT FORK
FRONT FORK
REMOVING THE FRONT FORKOrder Part name Q'ty Remarks Hold the machine by placing the suitable stand
under the engine. Refer to "HANDLING NOTE".
Front wheel Refer to "FRONT WHEEL AND REAR
WHEEL" section.
Front brake caliper Refer to "FRONT BRAKE AND REAR
BRAKE" section.
Headlight
Handlebar Refer to "HANDLEBAR" section.
1 Protector 1
2 Pinch bolt (upper bracket) 2 Only loosening.
3 Cap bolt 1 Loosen when disassembling the front fork.
4 Pinch bolt (lower bracket) 2 Only loosening.
5 Front fork 1

6-23
HANDLEBAR
HANDLEBAR
REMOVING THE HANDLEBAROrder Part name Q'ty Remarks Headlight
1 Hot starter cable 1 Disconnect at the lever side.
2 Hot starter lever holder 1
3 Clutch cable 1 Disconnect at the lever side.
4 Clutch lever holder 1 Disconnect the clutch switch lead.
5 Engine stop switch 1 Disconnect the engine stop switch lead.
6 Brake master cylinder 1 Refer to removal section.
7 Start switch 1 Disconnect the start switch lead.
8 Throttle cable cap 1
9 Throttle cable #1 (pulled) 1 Disconnect at the throttle side.
10 Throttle cable #2 (pushed) 1 Disconnect at the throttle side.
11 Right grip 1 Refer to removal section.
12 Tube guide 1
13 Left grip 1 Refer to removal section.
14 Handlebar upper holder 2
15 Handlebar 1
16 Handlebar lower holder 2