Yamaha WR250FM 2021, Owner'S Service Manual

Page: 223 / 404

CYLINDER HEAD
5-23
EAM30086
REMOVING THE CYLINDER HEAD
1. Remove:
•
Cylinder head bolt and nut
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.
• M9

135 mm (5.31 in): [4], [5], [6]
•
M9

145 mm (5.71 in): [3]
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
timing chain guide (intake side) and the cylin-
der head.
• Install the cylinder head gasket as shown in the
illustration.
x2 x 3 x1
FWD
6
1
2
3
5
4
6
1
2
3
5
4
Warpage limit
0.05 mm (0.0020 in)
Ne w