2006 YAMAHA YZ250F length

3 - 30
INSP
ADJ
SPROCKETS INSPECTION/DRIVE CHAIN INSPECTION
SPROCKETS INSPECTION
1. Inspect:
Sprocket teeth a
Excessive wear → Replace.
NOTE:
Replace the drive sprocket, rear wheel
sprocket and drive chain as a set.
DRIVE CHAIN INSPECTION
1. Measure:
Drive chain length (15 links) a
Out of specification → Replace.
NOTE:
While measuring the drive chain length, push
down on the drive chain to increase its ten-
sion.
Measure the length between drive chain
roller 1 and F as shown.
Perform this measurement at two or three
different places.
Drive chain length (15 links):
: 242.9 mm (9.563 in)
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 remove the
drive chain from the kerosene and dry the
drive chain.

3 - 36
INSP
ADJREAR SHOCK ABSORBER SPRING PRELOAD
ADJUSTMENT
REAR SHOCK ABSORBER SPRING
PRELOAD ADJUSTMENT
1. Elevate the rear wheel by placing the suit-
able stand under the engine.
2. Remove:
Rear frame
3. Loosen:
Locknut 1
4. Adjust:
Spring preload
By turning the adjuster 2.
* For EUROPE
NOTE:
Be sure to remove all dirt and mud from
around the locknut and adjuster before
adjustment.
The length of the spring (installed) changes
1.5 mm (0.06 in) per turn of the adjuster.
The I.D. mark b is marked at the end of the
spring.
The standard length and extent of adjust-
ment vary according to the quantity of I.D.
marks.
CAUTION:
Never attempt to turn the adjuster beyond
the maximum or minimum setting.Stiffer
→ Increase the spring preload.
(Turn the adjuster
2 in.)
Softer
→ Decrease the spring preload.
(Turn the adjuster
2 out.)
Spring length (installed)
a:
Standard length Extent of adjustment
One I.D. mark
257 mm (10.12 in)
*258 mm (10.16 in)
Two I.D. marks
263 mm (10.35 in)
*264 mm (10.39 in)
Three I.D. marks
254.5 mm (10.02 in)
*255.5 mm (10.06 in)245.5 ~ 263.5 mm
(9.67 ~ 10.37 in)
251.5 ~ 269.5 mm
(9.90 ~ 10.61 in)
243.0 ~ 261.0 mm
(9.57 ~ 10.28 in)
b

4 - 25
ENGCAMSHAFTS
5. Remove:
Exhaust camshaft 1
Intake camshaft 2
NOTE:
Attach a wire 3 to the timing chain to prevent
it from falling into the crankcase.
1
2
3
INSPECTION
Camshaft
1. Inspect:
Cam lobe
Pitting/scratches/blue discoloration →
Replace.
2. Measure:
Cam lobe length a and b
Out of specification → Replace.
Cam lobes length:
Intake:
a30.296 ~ 30.346 mm
(1.1923 ~ 1.1947 in)
: 30.196 mm
(1.1888 in)
b22.45 ~ 22.55 mm
(0.8839 ~ 0.8878 in)
: 22.35 mm
(0.8799 in)
Exhaust:
a30.399 ~ 30.499 mm
(1.1968 ~ 1.2007 in)
: 30.299 mm
(1.1929 in)
b22.45 ~ 22.55 mm
(0.8839 ~ 0.8878 in)
: 22.35 mm
(0.8799 in)
3. Measure:
Runout (camshaft)
Out of specification → Replace.
Runout (camshaft):
Less than 0.03 mm (0.0012 in)

4 - 40
ENGVALVES AND VALVE SPRINGS
Valve spring
1. Measure:
Valve spring free length a
Out of specification → Replace.
2. Measure:
Compressed spring force a
Out of specification → Replace.
b
Installed length
Free length (valve spring):
Intake:
37.81 mm (1.49 in)
: 36.81 mm (1.45 in)
Exhaust:
37.54 mm (1.48 in)
: 36.54 mm (1.44 in)
Compressed spring force:
Intake:
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)
Exhaust:
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)
3. Measure:
Spring tilt a
Out of specification → Replace.
Spring tilt limit:
Intake:
2.5°/1.7 mm (0.067 in)
Exhaust:
2.5°/1.6 mm (0.063 in)
Valve lifter
1. Inspect:
Valve lifter
Scratches/damage → Replace both lift-
ers and cylinder head.

4 - 52
ENGCLUTCH
EC4A3000
REMOVAL POINTS
Clutch boss
1. Remove:
Nut 1
Lock washer 2
Clutch boss 3
NOTE:
Straighten the lock washer tab and use the
clutch holding tool 4 to hold the clutch boss.
È
For USA and CDN
ÉExcept for USA and CDN
Clutch holding tool:
YM-91042/90890-04086
È
É
EC4A4000
INSPECTION
EC484100
Clutch housing and boss
1. Inspect:
Clutch housing 1
Cracks/wear/damage → Replace.
Clutch boss 2
Scoring/wear/damage → Replace.
EC484201
Primary driven gear
1. Check:
Circumferential play
Free play exists → Replace.
Gear teeth a
Wear/damage → Replace.
Clutch spring
1. Measure:
Clutch spring free length a
Out of specification → Replace springs
as a set.
Clutch spring free length:
40.4 mm (1.59 in)
: 39.4 mm (1.55 in)

5 - 31
CHAS
Base valve
1. Inspect:
Base valve 1
Wear/damage → Replace.
Contamination → Clean.
O-ring 2
Wear/damage → Replace.
Piston metal 3
Wear/damage → Replace.
Spring 4
Damage/fatigue → Replace base valve.
Air bleed screw 5
Wear/damage → Replace.
Collar
1. Inspect:
Piston metal 1
Wear/damage → Replace.
EC554400
Fork spring
1. Measure:
Fork spring free length a
Out of specification → Replace.
Fork spring free length:
454 mm (17.9 in)
: 449 mm (17.7 in)
FRONT FORK

5 - 67
CHASREAR SHOCK ABSORBER
2. Install:
•Spring seat 1
NOTE:
Install the spring seat with the projection a
brought into contact with the spring end, as
shown.
3. Tighten:
•Adjuster 1
4. Adjust:
•Spring length (installed)
Refer to “REAR SHOCK ABSORBER
SPRING PRELOAD ADJUSTMENT” sec-
tion in the CHAPTER 3.
5. Tighten:
•Locknut 1
Rear shock absorber
1. Install:
•Dust seal 1
•O-ring 2
•Collar 3
NOTE:
•Apply the molybdenum disulfide grease on
the dust seal lips and collars.
•Apply the lithium soap base grease on the O-
rings.

7 - 15
TUN
Front fork setting parts
•Front fork spring 1
NOTE:
The I.D. mark (slits) a is proved on the end of
the spring.TYPESPRING
RATESPRING PART
NUMBERI.D.
MARK
(slits)
SOFT0.398
0.408
0.418
0.4281C3-23141-A0
1C3-23141-B0
1C3-23141-C0
1C3-23141-D0I
II
III
IIII
STD 0.438 5XC-23141-M0–
STIFF0.449
0.459
0.469
0.4791C3-23141-F0
1C3-23141-G0
1C3-23141-H0
1C3-23141-J0I-I
I-II
I-III
I-IIII
EC72B000
Rear suspension setting
The rear suspension setting should be made
depending on the rider’s feeling of an actual
run and the circuit conditions.
The rear suspension setting includes the fol-
lowing two factors:
1. Setting of spring preload
•Change the set length of the spring.
•Change the spring.
2. Setting of damping force
•Change the rebound damping.
•Change the compression damping.
SETTING