Yamaha 2008 YZ250F Fahrer- Und Wartungshandbuch Seite 84

4. Measure:
• Camshaft-to-cap clearance
→
Out of specification
camshaft outside diameter.
Camshaft-to-cap clear-
ance:
0.028–0.062 mm
(0.0011–0.0024 in)
<Limit>:0.08 mm (0.003
in)
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.
Bolt (camshaft cap):
10 Nm (1.0 m•kg, 7.2
ft•lb)
• 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
the camshaft.
→
Within specification
camshaft case and camshaft
caps as a set.
Camshaft outside diame-
ter:
21.959–21.972 mm
(0.8645–0.8650 in)
Measure
CHECKING THE CAMSHAFT
SPROCKET
1. Inspect:
• Camshaft sprocket "1"
Wear/damage
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,
Replace
make sure that the tensioner rod
will come out smoothly.
Replace
• If not, replace the tensioner as-
sembly.
→
Replace the
4-17
CAMSHAFTS
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.