Yamaha YZ450FA 2011, Owner'S Service Manual

Page: 142 / 318

4-31
CYLINDER AND PISTON
REMOVING THE PISTON AND PISTON RING
1. Remove:
• Piston pin clip "1"
• Piston pin "2"
• Piston "3"
• Put identification marks on each piston head
for reference during reinstallation.
• Before removing each piston pin, deburr the
clip groove and pin hole area. If the piston pin
groove is deburred and the piston pin is still
difficult to remove, use the piston pin puller
set "4".
Do not use a hammer to drive the piston pin
out.
2. Remove:
• Piston ring "1"
Spread the end gaps apart while at the same
time lifting the piston ring over the top of the pis-
ton crown, as shown in the illustration.
CHECKING THE CYLINDER AND PISTON
1. Inspect:
• Cylinder and piston walls
Vertical scratches
→
Replace cylinder and
piston.
2. Measure:
• Piston-to-cylinder clearance
Measurement steps:
a. Measure the cylinder bore "C" with a cylin-
der bore gauge.
Measure the cylinder bore "C" in parallel to and
at right angles to the crankshaft. Then, find the
average of the measurements.
Piston pin puller set:
YU-1304/90890-01304
Cylinder bore "C"
97.00–97.01 mm
(3.8189–3.8193 in)
Taper limit "T" 0.05 mm (0.002 in)
Out of round "R" 0.05 mm (0.002 in)
"C" = Maximum D
"T" = (Maximum D
1
or D
2
) - (Maximum D
5
or
D
6
)
"R" = (Maximum D
1
, D
3
or D
5
) - (Minimum
D
2
, D
4
or D
6
)