Yamaha YZ 2019 Series, Owner'S Service Manual

Page: 226 / 398

VALVES AND VALVE SPRINGS
5-27
h. Install the valve into the cylinder head.
i. Press the valve through the valve guide and
onto the valve seat to make a clear impres-
sion.
j. Measure the valve seat contact width “c”
again. If the valve seat contact width is out of
specification, reface and lap the valve seat.
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EAM30093
CHECKING THE VALVE SPRINGS
1. Measure:
• Valve spring free length “a”
Out of specification

Replace the valve
spring.
EAM30094
CHECKING THE VALVE LIFTERS
1. Check:
•
Valve lifter
Damage/scratches

Replace the valve lift-
ers and cylinder head.
EAM30095
INSTALLING THE VALVES
1. Clean:
• Valve stem end
2. Lubricate:
•
Valve stem “1”
• Valve stem seal “2”
3. Install:
• Spring seat “1”
•
Valve stem seal “2”
• Valve “3”
•
Valve spring “4”
• Valve spring retainer “5”
(to the cylinder head)
TIP
• Make sure each valve is installed in its original
place.
• Install the valve springs with the larger pitch “a”
Free length (intake)
39.03 mm (1.54 in)
Limit
37.08 mm (1.46 in)
Free length (exhaust)
35.59 mm (1.40 in)
Limit
33.81 mm (1.33 in)
Recommended lubricant
Molybdenum disulfide oil
New