Yamaha YZ250F X 2008, Owner'S Service Manual

Page: 85 / 192

4-16
CAMSHAFTS
REMOVING THE CAMSHAFT
1. Remove:
• Timing mark accessing screw "1"
• Crankshaft end accessing screw
"2"
2. Align:
• T.D.C. mark
With align mark.
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 that 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.
3. Remove:
• Timing chain tensioner cap bolt
"1"
• Timing chain tensioner "2"
• Gasket
4. Remove:
• Bolt (camshaft cap) "1"
• Camshaft cap "2"
• Clip
Remove the bolts (camshaft cap) in a
crisscross pattern, working from the
outside in.
The bolts (camshaft cap) must be
removed evenly to prevent dam-
age to the cylinder head, cam-
shafts or camshaft caps.
5. Remove:
• Exhaust camshaft "1"
• Intake camshaft "2"
Attach a wire "3" to the timing chain to
prevent it from falling into the crank-
case.
CHECKING THE CAMSHAFT
1. Inspect:
• Cam lobe
Pitting/scratches/blue discolora-
tion
→
Replace.
2. Measure:
• Cam lobe length "a" and "b"
Out of specification
→
Replace.
3. Measure:
• Runout (camshaft)
Out of specification
→
Replace.
Cam lobes length:
Intake "a":
30.246–30.346 mm
(1.1908–1.1947 in)
<Limit>:
30.146 mm (1.1869 in)
Intake "b":
22.45–22.55 mm
(0.8839–0.8878 in)
<Limit>:
22.35 mm (0.8799 in)
Exhaust "a":
30.399–30.499 mm
(1.1968–1.2007 in)
<Limit>:
30.299 mm (1.1929 in)
Exhaust "b":
22.45–22.55 mm
(0.8839–0.8878 in)
<Limit>:
22.35 mm (0.8799 in)
Runout (camshaft):
Less than 0.03 mm
(0.0012 in)