Yamaha YZF-R15, Service Manual

Page: 185 / 338

5-23
CYLINDER AND PISTON
REMOVING THE PISTON
1. Remove:
• Piston pin clips “1”
• Piston pin “2”
• Piston “3”
CAUTION:
Do not use a hammer to drive the piston pin
out.
NOTE:
• Before removing the piston pin clip, cover the
crankcase opening with a clean rag to prevent
the piston pin clip from falling into the crank-
case.
• Before removing the piston pin, deburr the pis-
ton pin clip’s groove and the piston pin bore ar-
ea.
2. Remove:
• Top ring
• 2nd ring
• Oil ring
NOTE:
When removing a piston ring, open the end gap
with your fingers and lift the other side of the ring
over the piston crown.
CHECKING THE CYLINDER AND PISTON
1. Check:
• Piston wall
• Cylinder wall
Vertical scratches → Replace the cylinder,
and replace the piston and piston rings as a
set.
2. Measure:
• Piston-to-cylinder clearance
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 measurements.
1 2
3
Bore
56.985–57.010 mm
Taper limit
0.05 mm
Out of round limit
0.05 mm
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5-24
CYLINDER AND PISTON
b. If out of specification, replace the cylinder,
and replace the piston and piston rings as a
set.
c. Measure piston skirt diameter “D” “a”with the
micrometer.
d. If out of specification, replace the piston and
piston rings as a set.
e. Calculate the piston-to-cylinder clearance
with the following formula.
f. If out of specification, replace the cylinder,
and replace the piston and piston rings as a
set.
CHECKING THE PISTON RINGS
1. Measure:
• Piston ring side clearance
Out of specification → Replace the piston
and piston rings as a set.
Before measuring the piston ring side clearance,
eliminate any carbon deposits from the piston
ring grooves and piston rings.
2. Install:
• Piston ring
(into the cylinder)
Level the piston ring into the cylinder with the
piston crown.
“C” = maximum of D
1
2
–D
“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
- minimum of
D
2
, D
4
or D
6
b. 5.0 mm (0.20 in) from the bottom edge of the
piston
Piston
Diameter D
56.965–56.990 mm
• Piston-to-cylinder clearance =
Cylinder bore “C” -
Piston skirt diameter “D”
Piston-to-cylinder clearance
0.020–0.045 mm
Limit
0.15 mm
Piston ring
Top ring
Ring side clearance
0.030–0.065 mm
Limit
0.100 mm
2nd ring
Ring side clearance
0.020–0.055 mm
Limit
0.100 mm
a. 40 mm
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