Yamaha YZ450F 2021 - Removing the Cylinder Head; Checking the Timing Chain Guide (Intake Side); Checking the Cylinder Head; Installing the Cylinder Head

CYLINDER HEAD
5-23
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): [3], [4], [5], [6]
EAM30087
CHECKING THE TIMING CHAIN GUIDE
(INTAKE SIDE)
1. Check:
• Timing chain guide (intake side)
Damage/wear  Replace.
EAM30088
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 5-29.
• Cylinder head coolant passages
Mineral deposits/rust  Eliminate.
3. Measure:
• Cylinder head warpage
Out of specification  Resurface the cylinder
head.
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.
EAM30089
INSTALLING THE CYLINDER HEAD
1. Install:
• Timing chain guide (intake side) “1”
• Dowel pin “2”
• Cylinder head gasket “3”
• Cylinder head “4”
TIP
While pulling up the timing chain, install the tim-
ing chain guide (intake side) and the cylinder
head.
x2 x4
FWD
6
1
2
3
5
6
1
2
3
5
4
4
Warpage limit
0.05 mm (0.0020 in)
New