Yamaha 2011 WR250FA, Owner'S Service Manual

Page: 161 / 316

5-28
CYLINDER HEAD
CHECKING THE CYLINDER HEAD
1. Eliminate:
• Carbon deposits (from the combustion
chambers)
Use a rounded scraper.
Do not use a sharp instrument to avoid damag-
ing or scratching:
• Spark plug threads
• Valve seats
2. Inspect:
• Cylinder head
Scratches/damage
→
Replace.
Replace the titanium valves with the cylinder
head.
Refer to "CHECKING THE VALVE".
3. Measure:
• Cylinder head warpage
Out of specification
→
Resurface.
Warpage measurement and resurfacing
steps:
a. Place a straightedge and a feeler gauge
across the cylinder head.
b. Use a feeler gauge to measure the warpage.
c. If the warpage is out of specification, resur-
face the cylinder head.
d. Place a 400–600 grit wet sandpaper on the
surface plate, and resurface the head using
a figure-eight sanding pattern.
To ensure an even surface rotate the cylinder
head several times.
INSTALLING THE CYLINDER HEAD
1. Install:
• Dowel pin "1"
• Cylinder head gasket "2"
• Timing chain guide (exhaust side) "3"
• Cylinder head "4"
While pulling up the timing chain, install the tim-
ing chain guide (exhaust side) and cylinder
head.
2. Install:
• Washer "1"
• Cable guide "2"
• Bolts [L = 145 mm (5.71 in)] "3"
• Bolts [L = 135 mm (5.31 in)] "4"
• Nuts "5"
• Apply the molybdenum disulfide grease on
the thread and contact surface of the bolts.
• Follow the numerical order shown in the illus-
tration. Tighten the bolts and nuts in two stag-
es.
Cylinder head warpage:
Less than 0.05 mm (0.002 in)
Bolts [L = 145 mm (5.71 in)]:
38 Nm (3.8 m•kg, 27 ft•lb)
Bolts [L = 135 mm (5.31 in)]:
38 Nm (3.8 m•kg, 27 ft•lb)
Nuts:
10 Nm (1.0 m•kg, 7.2 ft•lb)