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YAMAHA YZ250F(D) Owner's Service Manual Page 96

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CHECKING THE CYLINDER HEAD
1. Eliminate:
• Carbon deposits (from the com-
bustion chambers)
Use a rounded scraper.
Do not use a sharp instrument to
avoid damaging 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.
Cylinder head warpage:
Less than 0.05 mm
(0.002 in)
Warpage measurement and resur-
facing 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 specifica-
tion, resurface the cylinder head.
d. Place a 400–600 grit wet sandpa-
per on the surface plate, and re-
surface 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, in-
stall the timing chain guide (exhaust
side) and cylinder head.
2. Install:
• Washer "1"
• Cable guide "2"
• Bolts [L = 145 mm (5.71 in)] "3"
Bolts [L = 145 mm (5.71
in)]:
38 Nm (3.8 m•kg, 27
ft•lb)
• Bolts [L = 135 mm (5.31 in)] "4"
Bolts [L = 135 mm (5.31
in)]:
38 Nm (3.8 m•kg, 27
ft•lb)
• Nuts "5"
Nuts:
10 Nm (1.0 m•kg, 7.2
ft•lb)
• Apply the molybdenum disulfide
grease on the thread and contact
surface of the bolts.
• Follow the numerical order shown
in the illustration. Tighten the bolts
and nuts in two stages.
4-22
CYLINDER HEAD
3. Install:
• Copper washer "1"
• Oil delivery pipe "2"
• Union bolt (M8) "3"
Union bolt (M8):
18 Nm (1.8 m•kg, 13
ft•lb)
• Union bolt (M10) "4"
Union bolt (M10):
20 Nm (2.0 m•kg, 14
ft•lb)
First tighten the union bolts temporar-
ily. Then retighten them with the width
"a" across flats of the oil delivery pipe
held tight with a spanner.
4. Install:
• Radiator pipe "1"
• Bolt (radiator pipe) "2"
Bolt (radiator pipe):
10 Nm (1.0 m•kg, 7.2
ft•lb)

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  • rodrigo Dec 03, 2017 02:34:
    MUY INTERESANT​E EL MANUAL PORQUE AYUDA PARA TENER A PUNTO UN MOTOR BIEN ARMADO TAL COMO INDICA EL MANUAL.