radiator YAMAHA WR 250F 2008 User Guide

3-14
ENGINE
ADJUSTING THE PILOT SCREW
1. Adjust:• Pilot screw "1"
Adjustment steps:
To optimize the fuel flow at a smaller
throttle opening, each machine's pilot
screw has been individually set at the
factory. Before adjusting the pilot
screw, turn it in fully and count the
number of turns. Record this number
as the factory-set number of turns
out.
a. Turn in the pilot screw until it is
lightly seated.
b. Turn out the pilot screw by the factory-set number of turns.
ADJUSTING THE ENGINE IDLING
SPEED
1. Start the engine and thoroughly warm it up.
2. Adjust: • Engine idling speed
Adjustment steps:
a. Turn the throttle stop screw "1"
until the specified engine idling
speed.
Using a digital engine tachometer for
idle speed adjustment, detect the en-
gine idling speed by bringing the
sensing element "c" of the engine ta-
chometer close to the ignition coil "2".
ADJUSTING THE VALVE
CLEARANCE
• The valve clearance should be ad0justed 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 "REMOVING THE SEAT,
FUEL TANK AND SIDE COV-
ERS" section.
2. Drain:
• CoolantRefer to "CHANGING THE
COOLANT" section.
3. Remove: • Right radiatorRefer to "RADIATOR" section in
the CHAPTER 5.
• Carburetor Refer to "CARBU RETOR" section
in the CHAPTER 5.
• Spark plug
• Upper engine bracket
• Cylinder head cover Refer to "CAMSHAFTS" section
in the CHAPTER 5. 4. Remove:
• Timing mark accessing screw "1"
• Crankshaft end accessing screw "2"
• O-ring
5. Check: • Valve clearanceOut 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 t hat 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.
Pilot screw (example):
1-1/2 turns out
(For EUROPE)
To increase idle speed →Turn the
throttle stop screw "1" in "a".
To decrease idle speed →Turn the
throttle stop screw "1" out "b".
Engine idling speed:1,750–1,950 r/min
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)

5-1
RADIATOR
ENGINE
RADIATOR
REMOVING THE RADIATOROrder Part name Q'ty Remarks Drain the coolant. Refer to "CHECKING THE COOLANT" sec-
tion in the CHAPTER 3.
Seat, fuel tank and left side cover Refer to "REMOVING THE SEAT, FUEL
TANK AND SIDE COVERS" section in the
CHAPTER 3.
1 Radiator guard 2
2 Radiator hose clamp 10 Only loosening.
3 Radiator hose 1 1
4 Left radiator 1
5 Radiator hose 3 1
6 Radiator pipe 2 1
7 Radiator hose 5 1
8 Catch tank hose 1
9 Right radiator 1
10 Radiator hose 2 1
11 Radiator hose 4 1
5

5-2
RADIATOR
12 Radiator pipe 11
13 Catch tank breather hose 1
14 Catch tank 1
Order
Part name Q'tyRemarks

5-3
RADIATOR
HANDLING NOTE
Do not remove the radiator cap
when the engine and radiator are
hot. Scalding hot fluid and steam
may be blown out under pressure,
which could cause serious injury.
When the engine has cooled, open
the radiator cap by the following
procedure:
Place a thick rag, like a towel, over
the radiator cap, slowly rotate the
cap counterclockwise to the de-
tent. This procedure allows any re-
sidual pressure to escape. When
the hissing sound has stopped,
press down on the cap while turn-
ing counterclockwise and remove
it.
CHECKING THE RADIATOR
1. Inspect:• Radiator core "1"
Obstruction →Blow out with com-
pressed air through rear of the ra-
diator.
Bent fin →Repair/replace.
INSTALLING THE RADIATOR
1. Install: • O-ring "1"
• Radiator pipe 1 "2"
• Bolt (radiator pipe) "3"
Apply the lithium soap base grease
on the O-ring.
2. Install:• Catch tank hose "1"
• Radiator hose 2 "2"
• Radiator hose 3 "3"
• Radiator pipe 2 "4"
• Radiator hose 5 "5"
• Radiator hose 4 "6"To right radiator "7".
3. Install: • Right radiator "1"
• Bolt (right radiator) "2"
• Radiator hose 5 "3"
Refer to "CABLE ROUTING DIA-
GRAM" section in the CHAPTER
2.
4. Install: • Left radiator "1"
• Bolt (left radiator) "2"
• Radiator hose 1 "3"
Refer to "CABLE ROUTING DIA-
GRAM" section in the CHAPTER
2.
5. Tighten:
• Radiator hose clamp "4" 6. Install:
• Radiator guard "1"
First fit the inner hook portion "a" and
then the outer one "b" onto the radia-
tor.
7. Install:• Catch tank "1"
• Bolt (catch tank) "2"
• Bolt (catch tank) "3"
• Catch tank hose "4"
• Catch tank breather hose "5"Refer to "CABLE ROUTING DIA-
GRAM" section in the CHAPTER
2.
Bolt (radiator pipe): 10 Nm (1.0 m•kg, 7.2
ft•lb)
Bolt (right radiator):10 Nm (1.0 m•kg, 7.2
ft•lb)
Bolt (left radiator): 10 Nm (1.0 m•kg, 7.2
ft•lb)
Radiator hose 1: 2 Nm (0.2 m•kg, 1.4
ft•lb)
Radiator hose clamp: 2 Nm (0.2 m•kg, 1.4
ft•lb)
Bolt (catch tank):
7 Nm (0.7 m•kg, 5.1
ft•lb)
Bolt (catch tank): 16 Nm (1.6 m•kg, 11
ft•lb)

5-19
CYLINDER HEAD
CYLINDER HEAD
REMOVING THE CYLINDER HEADOrder Part name Q'ty Remarks Seat and fuel tank Refer to "REMOVING THE SEAT, FUEL
TANK AND SIDE COVERS" section in the
CHAPTER 3.
Exhaust pipe and silencer Refer to "REMOVING THE EXHAUST PIPE
AND SILENCER" section in the CHAPTER 3.
Radiator hose 1 Disconnect at cylinder head side.
Carburetor Refer to "CARBURETOR" section.
Air cut-off valve assembly Refer to "AIR INDUCTION SYSTEM" section.
Camshaft Refer to "CAMSHAFTS" section.
Upper engine bracket Refer to "ENGINE REMOVAL" section.
1 Radiator pipe 1
2 Oil delivery pipe 1
3Nut 2
4 Bolt [L = 135 mm (5.31 in)] 2
5 Bolt [L = 145 mm (5.71 in)] 2
6 Cylinder head 1
7 Timing chain guide (exhaust side) 1

5-20
CYLINDER HEAD
CHECKING THE CYLINDER HEAD
1. Eliminate:• Carbon deposits (from the com-bustion chambers)
Use a rounded scraper.
Do not use a sharp instrument to
avoid damaging or scratching:
• Spark plug threads
• Valve seats
2. Inspect:• Cylinder head
Scratches/damage →Replace.
3. Measure: • Cylinder head warpage
Out of specification →Resurface.
Warpage measurement and resur-
facing steps:
a. Place a straightedge and a feeler
gauge across the cylinder head.
b. Use a feeler gauge to measure the warpage.
c. If the warpage is out of specifica-
tion, resurface the cylinder head.
d. Place a 400–600 grit wet sandpa- per on the surface plate, and re-
surface the head using a figure-
eight sanding pattern.
To ensure an even surface rotate the
cylinder head several times.
INSTALLING THE CYLINDER
HEAD
1. Install:
• Dowel pin "1"
• Cylinder head gasket "2"
• Timing chain guide (exhaust side) "3" • Cylinder head "4"
While pulling up the timing chain, in-
stall the timing chain guide (exhaust
side) and cylinder head.
2. Install:
• Washer "1"
• Cable guide "2"
• Bolts [L = 145 mm (5.71 in)] "3"
• Bolts [L = 135 mm (5.31 in)] "4"
•Nuts "5"
• Apply the molybdenum disulfide grease on the thread and contact
surface of the bolts.
• Follow the numerical order shown in the illustration. Tighten the bolts
and nuts in two stages.
3. Install:• Copper washer "1"
• Oil delivery pipe "2" • Union bolt (M8) "3"
• Union bolt (M10) "4"
4. Install: • Radiator pipe "1"
• Bolt (radiator pipe) "2"
Cylinder head warpage: Less than 0.05 mm
(0.002 in)
Bolts [L = 145 mm (5.71
in)]:38 Nm (3.8 m•kg, 27
ft•lb)
Bolts [L = 135 mm (5.31
in)]: 38 Nm (3.8 m•kg, 27
ft•lb)
Nuts: 10 Nm (1.0 m•kg, 7.2
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)
Bolt (radiator pipe): 10 Nm (1.0 m•kg, 7.2
ft•lb)

5-34
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 "REMOVING THE EXHAUST PIPE
AND SILENCER" section in the CHAPTER 3.
Brake pedal Refer to "ENGINE REMOVAL" section.
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.

5-53
ENGINE REMOVAL
ENGINE REMOVAL
REMOVING THE ENGINEOrder Part name Q'ty Remarks Hold the machine by placing the suitable stand
under the frame. Refer to "HANDLING NOTE".
Drain the engine oil. Refer to "CHANGING THE ENGINE OIL"
section in the CHAPTER 3.
Seat and fuel tank Refer to "REMOVING THE SEAT, FUEL
TANK AND SIDE COVERS" section in the
CHAPTER 3.
Carburetor Refer to "CARBURETOR" section.
Exhaust pipe and silencer Refer to "REMOVING THE EXHAUST PIPE
AND SILENCER" section in the CHAPTER 3.
Air cut-off valve assembly Refer to "AIR INDUCTION SYSTEM" section.
Clutch cable Disconnect at the engine side.
Radiator Refer to "RADIATOR" section.
Shift pedal Refer to "AC MAGNETO AND STARTER
CLUTCH" section.
Cylinder head breather hose Refer to "CAMSHAFTS" section.
Oil hose and oil tank breather ho seRefer to "OIL PUMP" section.
Ignition coil