Removing The Cylinder Head; Checking The Timing Chain Guide (Intake Side); Checking The Cylinder Head - Yamaha YZ450FX 2019 Owner's Service Manual

EAM30086

REMOVING THE CYLINDER HEAD

1. Remove:
• Cylinder head bolt
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.
• M6  35 mm (1.38 in): "1"–"2"
• M10  149 mm (5.87 in): "4", "5", "6"
• M10  165 mm (6.49 in): "3"
x2 x3 x1
4 4
1 1
2 2
6 6
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CHECKING THE TIMING CHAIN GUIDE
(INTAKE SIDE)
1. Check:
• Timing chain guide (intake side)
Damage/wear  Replace.
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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.
FWD
5 5
3 3
5-21
CYLINDER HEAD
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 cylinder
head.
Warpage limit
0.05 mm (0.0020 in)
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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 cylinder
head as follows.
d. Place a 400–600 grit wet sandpaper on a sur-
face 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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