Checking The Timing Chain Guides; Checking The Timing Chain Tensioner - Yamaha 2009 YFM25RY Service Manual

2. Check:
• Cylinder head
Damage/scratches → Replace.
3. Measure:
• Cylinder head warpage
Out of specification → Resurface the cyl-
inder head.
Warpage limit
0.05 mm (0.0020 in)
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a. Place a straightedge "1" and a thickness
gauge "2" 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 the
surface plate and resurface the cylinder
head using a figure-eight sanding pattern.
TIP
To ensure an even surface, rotate the cylinder
head several times.
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EAS24180

CHECKING THE TIMING CHAIN GUIDES

The following procedure applies to all of the
camshaft sprockets and timing chain guides.
1. Check:
• Camshaft sprocket
More than 1/4 tooth wear "a" → Replace
the camshaft sprockets and the timing
chain as a set.
a. 1/4 tooth
b. Correct
1. Timing chain
2. Camshaft sprocket
2. Check:
• Timing chain guide (exhaust side)
Damage/wear → Replace the defective
part(s).
EAS24200
CHECKING THE TIMING CHAIN TEN-
SIONER
1. Check:
• Timing chain tensioner
Cracks/damage → Replace.
2. Check:
• One-way cam operation
Rough movement → Replace the timing
chain tensioner housing.
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a. Lightly press the timing chain tensioner rod
into the timing chain tensioner housing by
hand.
TIP
While pressing the timing chain tensioner rod,
wind it clockwise with a thin screwdriver "1"
until it stops.
b. Remove the screwdriver and slowly release
the timing chain tensioner rod.
c. Make sure that the timing chain tensioner
rod comes out of the timing chain tensioner
housing smoothly. If there is rough move-
ment, replace the timing chain tensioner.
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5-13
CYLINDER HEAD