Yamaha YZ 2015 Series, Owner'S Service Manual

Page: 225 / 396

CYLINDER HEAD
5-22
EASB291221
REMOVING THE CYLINDER HEAD
1. Remove:
• Intake camshaft
• Exhaust camshaft
Refer to “REMOVING THE CAMSHAFT” on
page 5-14.
2. Remove:
• Cylinder head nuts
• Cylinder head bolts
TIP
• Loosen the bolts in the proper sequence as
shown.
• Loosen each bolt 1/2 of a turn at a time. After
fully loosening all the bolts, remove them.
EASB291222
CHECKING THE TIMING CHAIN GUIDE (IN-
TAKE SIDE)
1. Check:
• Timing chain guide (intake side)
Damage/wear

Replace.
EASB291223 CHECKING THE CYLINDER HEAD
1. Eliminate:
• Combustion chamber carbon deposits
TIP
Use a rounded scraper, not a sharp instrument,
in order not to damage or scratch the spark
plug bore threads.
2. Check:
• Cylinder head
Damage/scratches

Replace.
TIP
When replacing the cylinder head, replace also
the valve.
Refer to “CHECKING THE VALVE SEATS” on
page 5-27.
• Cylinder head coolant passages
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 and a thickness gauge
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 a
surface plate, and resurface the cylinder
head using a figure-eight sanding pattern.
TIP
To ensure an even surface, turn the cylinder
head several times.
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6
1
2
3
5
4
x2 x4
FWD
Warpage limit
0.05 mm (0.0020 in)