Yamaha 2004 YP400, Service Manual, Page: 232 / 417

5 - 19
ENG
CYLINDER HEAD
EAS00222
REMOVING THE CYLINDER HEAD
1. Remove:
• cylinder head nuts
NOTE:
_
• Loosen the cylinder head nuts in the proper
sequence as shown.
• Loosen each cylinder head nut 1/2 of a turn
at a time. After all of the cylinder head nuts
are fully loosened, remove them.
EAS00229
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.
• cylinder head water jacket
Mineral deposits/rust
→
Eliminate.
3. Measure:
• cylinder head warpage
Out of specification
→
Resurface the cylin-
der 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 cylin-
der 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, rotate the cylinder
head several times.
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Maximum cylinder head warpage
0.05 mm (0.002 in)
2
3
4
1
2
1