Yamaha VINO YJ50RAP, Service Manual

Page: 126 / 228

5 - 7
ENG
CYLINDER HEAD, CYLINDER AND PISTON
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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.
NOTE:
@
To ensure an even surface, rotate the cylinder
head several times.
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1
2
EAS00255
CHECKING THE CYLINDER AND PISTON
1. Check:
• piston wall
• cylinder wall
Vertical scratches
→
Rebore or replace the
cylinder, and replace the piston and piston
rings as a set.
2. Measure:
• piston-to-cylinder clearance
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a. Measure cylinder bore “C” with the cylinder
bore gauge.
NOTE:
@
Measure cylinder bore “C” by taking side-to-
side and front-to-back measurements of the
cylinder. Then, find the average of the mea-
surements.
Cylinder bore “C”
39.993 ~ 40.012 mm
(1.5745 ~ 1.5753 in)
Max. taper “T” 0.05 mm (0.002 in)
Out-of-round “R” 0.05 mm (0.002 in)
“C” = maximum of D
1
~ D
6
“T” = maximum of D
1
or D
2
– maximum of
D
5
or D
6
“R” = maximum of D
1
, D
3
or D
5
– mini-
mum of D
2
, D
4
or D
6
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