Yamaha XT250X 2008, Service Manual

Page: 155 / 282

CYLINDER HEAD
5-9
EAS24160
CHECKING THE CYLINDER HEAD
1. Eliminate:
●
Combustion chamber carbon deposits
(with a rounded scraper)
NOTE:
Do not use a sharp instrument to avoid damag-
ing or scratching:
●
Spark plug bore threads
●
Valve seats
2. Check:
●
Cylinder head
Damage/scratches
→
Replace.
3. Measure:
●
Cylinder head warpage
Out of specification
→
Resurface the cylinder
head.
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a. Place a straightedge “1” and a thickness
gauge “2” across the cylinder head.
b. Measure the warpage.
c. If the limit is exceeded, resurface the cylinder
head as follows.
d. Place a 400
–
600 grit wet sandpaper on the
surface plate and resurface the cylinder head
using a figure-eight sanding pattern.
NOTE:
To ensure an even surface, turn the cylinder
head several times.
e. When the cylinder head warpage is out of
specification after resurfacing, replace the
cylinder head.
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EAS23940
CHECKING THE TAPPET COVERS AND
CAMSHAFT SPROCKET COVER
The following procedure applies to both of the
tappet covers and O-rings.
1. Check:
●
Tappet cover
●
Camshaft sprocket cover
EAS3C51005
CHECKING THE CAMSHAFT SPROCKET
AND TIMING CHAIN GUIDE (EXHAUST
SYSTEM SIDE)
Check the camshaft sprocket and the timing
chain guide (exhaust system side) as follows.
1. Check:
●
Camshaft sprocket
Wear of 1/4 or more teeth “a”
→
Replace the
camshaft sprocket as a set, timing chain, and
crankshaft sprocket.
Warpage limit
0.03 mm (0.0012 in)
4
5
6
2
1
3
a. 1/4 tooth wear
b. Normal
1. Timing chain
2. Camshaft sprocket
1
2
a
b
1
2
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