2008 YAMAHA YZ250F set clock

2-5
MAINTENANCE SPECIFICATIONS
Stem runout limit----0.01 mm
(0.0004 in)
Valve seat width (IN) 0.9–1.1 mm (0.0354–0.0433 in)1.6 mm (0.0630
in)
Valve seat width (EX) 0.9–1.1 mm (0.0354–0.0433 in)1.6 mm (0.0630
in)
Valve spring: Free length (IN) 37.81 mm (1.49 in)36.81 mm (1.45
in)
Free length (EX) 37.54 mm (1.48 in)36.54 mm (1.44
in)
Set length (valve closed) (IN) 29.13 mm (1.15 in)----
Set length (valve closed) (EX) 29.30 mm (1.15 in)----
Compressed force (installed) (IN) 99–114 N at 29.13 mm (9.9–11.4 kg at
29.13 mm, 22.27–25.57 lb at 1.15 in) ----
Compressed force (installed) (EX) 126–144 N at 29.30 mm (12.6–14.4 kg at
29.30 mm, 28.44–32.41 lb at 1.15 in) ----
Tilt limit* (IN) ----2.5°/1.7 mm
(2.5°/0.067 in)
Tilt limit* (EX) ----2.5°/1.6 mm
(2.5°/0.063 in)
Direction of winding (top view) (IN) Clockwise----
Direction of winding (top view) (EX) Clockwise----
Piston: Piston to cylinder clearance 0.030–0.055 mm (0.0012–0.0022 in) 0.1 mm (0.004
in)
Piston size "D" 76.955–76.970 mm (3.0297–3.0303 in) ----
Measuring point "H" 8 mm (0.31 in)----
Piston off-set 0.5 mm (0.020 in)/IN-side----
Piston pin bore inside diameter 16.002–16.013 mm (0.6300–0.6304 in) 16.043 mm
(0.6316 in)
Item
StandardLimit

4-17
CAMSHAFTS
4. Measure:• Camshaft-to-cap clearanceOut of specification
→Measure
camshaft outside diameter.
Measurement steps:
a. Install the camshaft onto the cylin-
der head.
b. Position a strip of Plastigauge
®
"1" onto the camshaft.
c. Install the clip, dowel pins and camshaft caps.
• Tighten the bolts (camshaft cap) in a crisscross pattern from innermost
to outer caps.
• Do not turn the camshaft when measuring clearance with the Plas-
tigauge
®.
d. Remove the camshaft caps and measure the width of the Plasti-
gauge
® "1".
5. Measure:• Camshaft outside diameter "a"Out of specification
→Replace
the camshaft.
Within specification
→Replace
camshaft case and camshaft
caps as a set. CHECKING THE CAMSHAFT
SPROCKET
1. Inspect:
• Camshaft sprocket "1"
Wear/damage
→Replace the
camshaft assembly and timing
chain as a set.
CHECKING THE
DECOMPRESSION SYSTEM
1. Check: • Decompression system
Checking steps:
a. Check that the decompression mechanism cam "1" moves
smoothly.
b. Check that the decompression
mechanism cam lever pin "2"
projects from the camshaft.
CHECKING THE TIMING CHAIN
TENSIONER
1. Check:• While pressing the tensioner rod
lightly with fingers, use a thin
screwdriver "1" and wind the ten-
sioner rod up fully clockwise.
• When releasing the screwdriver by pressing lightly with fingers,
make sure that the tensioner rod
will come out smoothly.
• If not, replace the tensioner as- sembly. INSTALLING THE CAMSHAFT
1. Install:
• Exhaust camshaft "1"
• Intake camshaft "2"
Installation steps:
a. Turn the crankshaft counterclock- wise with a wrench.
• Apply the molybdenum disulfide oil
on the camshafts.
• Apply the engine oil on the decom- pression system.
• Squeezing the decompression le- ver allows the crankshaft to be
turned easily.
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.
Camshaft-to-cap clear-
ance:
0.028–0.062 mm
(0.0011–0.0024 in)
:0.08 mm (0.003
in)
Bolt (camshaft cap): 10 Nm (1.0 m•kg, 7.2
ft•lb)
Camshaft outside diame-
ter: 21.959–21.972 mm
(0.8645–0.8650 in)

7-9
CHASSIS
SUSPENSION SETTING (FRONT FORK)
• If any of the following symptoms is experienced with the standard position as the base, make resetting by reference to the adjustment procedure given in the same chart.
• Before any change, set the rear shock absorber sunken length to the standard figure 90–100 mm (3.5–3.9 in).
Symptom Section
Check Adjust
Jump Large
gap Medi-
um
gap Small
gap
Stiff over entire
range
○○○
Compression damping Turn adjuster counterclockwise (about 2 clicks) to decrease damping.
Oil amount Decrease oil amount by about 5–10 cm
3 (0.2–0.4
Imp oz, 0.2–0.3 US oz).
Spring Replace with soft spring.
Unsmooth move-
ment over entire
range
○○○○
Outer tube Check for any bends, dents, and other noticeable
scars, etc. If any, replace affected parts.
Inner tube
Slide metal Replace with a new one for extended use.
Piston metal Replace with a new one for extended use.
Under bracket tighten-
ing torque Retighten to specified torque.
Poor initial move-
ment
○
Rebound damping Turn adjuster counterclockwise (about 2 clicks) to decrease damping.
Oil seal Apply grease in oil seal wall.
Soft over entire
range, bottoming
out
○○
Compression damping Turn adjuster clockwise (about 2 clicks) to in- crease damping.
Oil amount Increase oil amount by about 5–10 cm
3 (0.2–0.4
Imp oz, 0.2–0.3 US oz).
Spring Replace with stiff spring.
Stiff toward stroke
end
○Oil amount Decrease oil amount by about 5 cm3 (0.2 Imp
oz,0.2 US oz).
Soft toward stroke
end, bottoming out
○Oil amount Increase oil amount by about 5 cm3 (0.2 Imp
oz,0.2 US oz).
Stiff initial move-
ment
○○○○Compression damping Turn adjuster counterclockwise (about 2 clicks) to
decrease damping.
Low front, tending to
lower front posture
○○
Compression damping Turn adjuster clockwise (about 2 clicks) to in- crease damping.
Rebound damping Turn adjuster counterclockwise (about 2 clicks) to decrease damping.
Balance with rear end Set sunken length for 95–100 mm (3.7–3.9 in) when one passenger is astride seat (lower rear
posture).
Oil amount Increase oil amount by about 5 cm
3 (0.2 Imp oz,
0.2 US oz).
"Obtrusive" front,
tending to upper
front posture
○○
Compression damping Turn adjuster counterclockwise (about 2 clicks) to decrease damping.
Balance with rear end Set sunken length for 90–95 mm (3.5–3.7 in) when one passenger is astride seat (upper rear
posture).
Spring Replace with soft spring.
Oil amount Decrease oil amount by about 5–10 cm
3 (0.2–0.4
Imp oz, 0.2–0.3 US oz).

7-10
CHASSIS
SUSPENSION SETTING (REAR SHOCK ABSORBER)
• If any of the following symptoms is experienced with the standard position as the base, make resetting by reference to the adjustment procedure given in the same chart.
• Adjust the rebound damping in 2-click increments or decrements.
• Adjust the low compression damping in 1-click increments or decrements.
• Adjust the high compression damping in 1/6 turn increments or decrements.
Symptom Section
Check Adjust
Jump Large
gap Medi-
um
gap Small
gap
Stiff, tending to sink
○○
Rebound damping Turn adjuster counterclockwise (about 2 clicks) to decrease damping.
Spring set length Set sunken length for 90–100 mm (3.5–3.9 in) when one passenger is astride seat.
Spongy and unsta-
ble
○○
Rebound damping Turn adjuster clockwise (about 2 clicks) to in- crease damping.
Low compression
damping Turn adjuster clockwise (about 1 click) to increase
damping.
Spring Replace with stiff spring.
Heavy and dragging
○○
Rebound damping Turn adjuster counterclockwise (about 2 clicks) to decrease damping.
Spring Replace with soft spring.
Poor road gripping
○
Rebound damping Turn adjuster counterclockwise (about 2 clicks) to decrease damping.
Low compression
damping Turn adjuster clockwise (about 1 clicks) to in-
crease damping.
High compression
damping Turn adjuster clockwise (about 1/6 turn) to in-
crease damping.
Spring set length Set sunken length for 90–100 mm (3.5–3.9 in) when one passenger is astride seat.
Spring Replace with soft spring.
Bottoming out
○○
High compression
damping Turn adjuster clockwise (about 1/6 turn) to in-
crease damping.
Spring set length Set sunken length for 90–100 mm (3.5–3.9 in) when one passenger is astride seat.
Spring Replace with stiff spring.
Bouncing
○○
Rebound damping Turn adjuster clockwise (about 2 clicks) to in- crease damping.
Spring Replace with soft spring.
Stiff travel
○○
High compression
damping Turn adjuster counterclockwise (about 1/6 turn) to
decrease damping.
Spring set length Set sunken length for 90–100 mm (3.5–3.9 in) when one passenger is astride seat.
Spring Replace with soft spring.