2008 YAMAHA YZ250F ABS

5-37
REAR SHOCK ABSORBER
REAR SHOCK ABSORBER
REMOVING THE REAR SHOCK ABSORBEROrder Part name Q'ty Remarks Hold the machine by placing the suitable stand
under the engine. Refer to "HANDLING NOTE".
Seat Refer to "SEAT, FUEL TANK AND SIDE
COVERS" section in the CHAPTER 4.
Silencer Refer to "EXHAUST PIPE AND SILENCER"
section in the CHAPTER 4.
1 Clamp (air filter joint) 1 Only loosening.
2 Rear frame 1
3 Bolt (rear shock absorber-relay arm) 1 Hold the swingarm.
4 Bolt (rear shock absorber-frame) 1
5 Rear shock absorber 1
6 Locknut 1 Only loosening.
7 Adjuster 1 Only loosening.
8 Spring seat 2
9 Lower spring guide 1
10 Upper spring guide 1
11 Spring (rear shock absorber) 1

5-38
REAR SHOCK ABSORBER
12 Bearing2 Refer to removal section.
Order
Part name Q'tyRemarks

5-39
REAR SHOCK ABSORBER
HANDLING NOTE
• Support the machine securely so there is no danger of it falling
over.
• This rear shock absorber is pro-
vided with a separate type tank
filled with high-pressure nitro-
gen gas. To prevent the danger
of explosion, read and under-
stand the following information
before handling the shock ab-
sorber. The manufacturer can
not be held responsible for prop-
erty damage or personal injury
that may result from improper
handling.
• Never tamper or attempt to dis-assemble the cylinder or the
tank.
• Never throw the rear shock ab-
sorber into an open flame or
other high heat. The rear shock
absorber may explode as a re-
sult of nitrogen gas expansion
and/ or damage to the hose.
• Be careful not to damage any
part of the gas tank. A damaged
gas tank will impair the damp-
ing performance or cause a
malfunction.
• Take care not to scratch the contact surface of the piston
rod with the cylinder; or oil
could leak out.
• Never attempt to remove the plug at the bottom of the nitro-
gen gas tank. It is very danger-
ous to remove the plug.
• When scrapping the rear shock
absorber, follow the instruc-
tions on disposal.
NOTES ON DISPOSAL (YAMAHA
DEALERS ONLY)
Before disposing the rear shock ab-
sorber, be sure to extract the nitrogen
gas from valve "1". Wear eye protec-
tion to prevent eye damage from es-
caping gas and/or metal chips.
To dispose of a damaged or worn-
out rear shock absorber, take the
unit to your Yamaha dealer for this
disposal procedure.
REMOVING THE BEARING
1. Remove:• Stopper ring (upper bearing) "1"
Press in the bearing while pressing its
outer race and remove the stopper
ring.
2. Remove:• Upper bearing "1"
Remove the bearing by pressing its
outer race.
3. Remove:• Lower bearing "1"
Remove the bearing by pressing its
outer race.
CHECKING THE REAR SHOCK
ABSORBER
1. Inspect:
• Damper rod "1"Bends/damage
→Replace rear
shock absorber assembly.
• Shock absorber "2" Oil leaks
→Replace rear shock
absorber assembly.
Gas leaks
→Replace rear shock
absorber assembly. • Spring "3"
Damage
→Replace spring.
Fatigue
→Replace spring.
Move spring up and down.
• Spring guide "4" Wear/damage
→Replace spring
guide.
• Spring seat "5" Cracks/damage
→Replace.
• Bearing "6"
Free play exists/unsmooth revolu-
tion/rust
→Replace.
INSTALLING THE BEARING
1. Install: • Upper bearing "1"
Install the bearing parallel until the
stopper ring groove appears by
pressing its outer race.
Do not apply the grease on the
bearing outer race because it will
wear the rear shock absorber sur-
face on which the bearing is press
fitted.
2. Install:• Stopper ring (upper bearing) "1"
After installing the stopper ring, push
back the bearing until it contacts the
stopper ring.

5-40
REAR SHOCK ABSORBER
3. Install:• Lower bearing "1"
Install the bearing by pressing it on
the side having the manufacture's
marks or numbers.
INSTALLING THE SPRING (REAR
SHOCK ABSORBER)
1. Install:• Spring "1"
• Upper spring guide "2"
• Lower spring guide "3"
2. Install: • Spring seat "1"
Install the spring seat with the projec-
tion "a" brought into contact with the
spring end, as shown.
3. Tighten:•Adjuster "1" 4. Adjust:
• Spring length (installed)Refer to "ADJUSTING THE
REAR SHOCK ABSORBER
SPRING PRELOAD" section in
the CHAPTER 3.
5. Tighten:
• Locknut "1"
INSTALLING THE REAR SHOCK
ABSORBER
1. Install: • Dust seal "1"
• O-ring "2"
•Collar "3"
• Apply the molybdenum disulfide grease on the dust seal lips and col-
lars.
• Apply the lithium soap base grease on the O-rings.
2. Install:• Bushing "1"
•Collar "2"
• Dust seal "3"
• Apply the molybdenum disulfide grease on the bearing and dust seal
lips.
• Install the dust seals with their lips
facing outward.
3. Install:• Rear shock absorber
4. Install: • Bolt (rear shock absorber-frame)
"1"
• Washer "2"
• Nut (rear shock absorber-frame) "3"
Apply the molybdenum disulfide
grease on the bolt.
5. Install:• Bolt (rear shock absorber-relay arm) "1"
• Nut (rear shock absorber-relay
arm) "2"
Apply the molybdenum disulfide
grease on the bolt.
6. Install:• Rear frame "1"
• Bolt [rear frame (upper)] "2"
Installed depth of the
bearing "a":
4 mm (0.16 in)
Nut (rear shock absorb-
er-frame):56 Nm (5.6 m•kg, 40
ft•lb)
Nut (rear shock absorb-
er-relay arm): 53 Nm (5.3 m•kg, 38
ft•lb)
Bolt [rear frame (upper)]: 38 Nm (3.8 m•kg, 27
ft•lb)

5-41
REAR SHOCK ABSORBER
• Bolt [rear frame (lower)] "3"
7. Tighten: • Bolt (air filter joint) "1" Bolt [rear frame (lower)]:
32 Nm (3.2 m•kg, 23
ft•lb)
Bolt (air filter joint): 3 Nm (0.3 m•kg, 2.2
ft•lb)

7-8
CHASSIS
When using a rear shock absorber
other than currently installed, use
the one whose overall length "a"
does not exceed the standard as it
may result in faulty performance.
Never use one whose overall
length is greater than standard.
REAR SHOCK ABSORBER
SETTING PARTS
• Rear shock spring "1"
[Equal-pitch titanium spring]
[Equal-pitch steel spring][Unequal-pitch steel spring]
Install the spring seat "2" to the ti-
tanium spring.
• The unequal-pitch spring is softer in
initial characteristic than the equal-
pitch spring and is difficult to bottom
out under full compression.
• The I.D. mark "a" is marked at the end of the spring.
• Spring specification varies accord-
ing to the color and quantity of I.D.
marks.
• Extent of adjustment (spring length) [Titanium spring]
[Steel spring]
Length "a" of standard
shock:
490 mm (19.29 in)
T
Y
P
E SPRI
NG
RAT
E SPRING
PART
NUM-
BER -
22212- I.D.
MARK SPR
ING
FRE E
LEN
GTH
(ap-
prox
.)
S
O F
T 4.5 1C3-00 Green 265
4.7 1C3-10 Red 265
4.9 1C3-20 Black 265
5.1 1C3-30 Blue 265
S T
D 5.3
1C3-40
(1C3-A0) Yellow 275
S
TI
F
F 5.5 1C3-50 Pink 275
5.7 1C3-60 White 275
T
Y
P
E SPRI
NG
RAT
E SPRING
PART NUM-
BER -
22212- I.D.
MARK/
Q'TY SPR
ING
FRE E
LEN
GTH
4.3 5UN-00 Brown/1 260
T
Y
P
E SPRI
NG
RAT
E
(ap-
prox. ) SPRING
PART
NUM-
BER -
22212- I.D.
MARK/ Q'TY SPR
ING
FRE E
LEN
GTH
S
O
F
T 4.5 5UN-A0 Green/2 275
4.75UN-B0Red/2275
4.9 5UN-C0 Black/2 275
5.1 5UN-D0 Blue/2 275
5.3 5UN-E0
Yellow/
2 275
5.5 5UN-F0 Pink/2 275
S
TI F
F 5.7
5UN-
22212- G0 White/2 275
SPRING
FREE
LENGTH EXTENT OF AD-
JUSTMENT "b"
Approx. 265 mm
(10.43 in) One I.D. mark
245.5–263.5 mm (9.67–10.37 in)
Two I.D. marks
251.5–269.5 mm (9.90–10.61 in)
Three I.D. marks 243.0–261.0 mm (9.57–10.28 in)
Approx. 275 mm
(10.83 in) One I.D. mark
255.5–273.5 mm (10.06–10.77 in)
Two I.D. marks
261.5–279.5 mm (10.30–11.00 in)
Three I.D. marks 253.0–271.0 mm (9.96–10.67 in)
SPRING FREE
LENGTH EXTENT OF AD-
JUSTMENT "b"
260 mm
(10.24 in) 240.5–258.5 mm
(9.47–10.18 in)
275 mm
(10.83 in) 255.5–273.5 mm
(10.06–10.77 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.