Yamaha SR400 2014, Service Manual

Page: 182 / 342

CYLINDER HEAD
5-8
7. Remove:
• Cylinder head “1”
TIP
•
Loosen the bolts and nuts in the proper se-
quence.
•
Loosen each bolt and nut 1/2 of a turn at a
time. After all of the bolts and nuts are fully
loosened, remove them.
EAS24160
CHECKING THE CYLINDER HEAD
1. Eliminate:
• Combustion chamber carbon deposits
(with a rounded scraper)
TIP
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 mating surface of 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.
TIP
To ensure an even surface, rotate 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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EAS23840
CHECKING THE CAMSHAFT
1. Check:
• Camshaft lobe
Blue discoloration/pitting/scratches

Re-
place the camshaft.
2. Measure:
• Camshaft lobe dimensions “a” and “b”
Out of specification

Replace the camshaft.
1
2
3
4
1
Warpage limit
0.03 mm (0.0012 in)
1
2