Yamaha YZ450F Owner's Service Manual page 105

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 re-
installation.
• Before removing each piston pin,
deburr the clip groove and pin hole
area. If the piston pin groove is de-
burred and the piston pin is still dif-
ficult to remove, use the piston pin
puller set "4".
Piston pin puller set:
YU-1304/90890-01304
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 piston crown, as
shown in the illustration.
CHECKING THE CYLINDER AND
PISTON
1. Inspect:
• Cylinder and piston walls
Vertical scratches → Replace cyl-
inder and piston.
2. Measure:
• Piston-to-cylinder clearance
Measurement steps:
a. Measure the cylinder bore "C"
with a cylinder bore gauge.
Measure the cylinder bore "C" in par-
allel to and at right angles to the
crankshaft. Then, find the average of
the measurements.
Cylinder 97.00–97.01 mm
bore "C" (3.8189–3.8193 in)
Taper limit
0.05 mm (0.002 in)
"T"
Out of
0.05 mm (0.002 in)
round "R"
"C" = Maximum D
"T" = (Maximum D or D
1
imum D or D )
5 6
"R" = (Maximum D , D
1 3
(Minimum D , D
2 4
b. If out of specification, replace the
cylinder, and replace the piston
and piston rings as set.
c. Measure the piston skirt diameter
"P" with a micrometer.
a. 9 mm (0.35 in) from the piston
bottom edge.
Piston size "P"
96.965–96.980 mm
Standard
(3.8175–3.8181 in)
d. If out of specification, replace the
piston and piston rings as a set.
4-24
CYLINDER AND PISTON
e. Calculate the piston-to-cylinder
clearance with following formula:
Piston-to-cylinder clearance =
Cylinder bore "C" - Piston skirt
diameter "P"
f. If out of specification, replace the
cylinder, and replace the piston
and piston rings as set.
CHECKING THE PISTON RING
1. Measure:
• Ring side clearance
Use a feeler gauge "1".
Out of specification → Replace
the piston and rings as a set.
Clean carbon from the piston ring
grooves and rings before measuring
the side clearance.
) - (Max-
2
or D ) -
5
or D )
6
Top
ring
2nd
ring
Piston-to-cylinder clear-
ance:
0.020–0.045 mm
(0.0008–0.0018 in)
<Limit>:0.1 mm (0.004
in)
Side clearance:
Standard <Limit>
0.015–0.065
mm 0.12 mm
(0.0006–0.0 (0.005 in)
026 in)
0.020–0.060
mm 0.12 mm
(0.0008–0.0 (0.005 in)
024 in)