Yamaha WR250F 2008 Owner's And Service Manual page 123

3. Measure:
• Ring end gap
Out of specification → Replace.
You cannot measure the end gap on
the expander spacer of the oil control
ring. If the oil control ring rails show
excessive gap, replace all three rings.
End gap:
Standard
Top 0.15–0.25 mm
ring (0.006–0.010 in)
2nd 0.30–0.45 mm
ring (0.012–0.018 in)
Oil 0.10–0.40 mm
ring (0.004–0.016 in)
CHECKING THE PISTON PIN
1. Inspect:
• Piston pin
Blue discoloration/grooves → Re-
place, then inspect the lubrication
system.
2. Measure:
• Piston pin-to-piston clearance
Measurement steps:
a. Measure the outside diameter
(piston pin) "a".
If out of specification, replace the
piston pin.
Outside diameter (piston
pin):
15.991–16.000 mm
(0.6296–0.6299 in)
b. Measure the inside diameter (pis-
ton) "b".
Inside diameter (piston):
16.002–16.013 mm
(0.6300–0.6304 in)
c. Calculate the piston pin-to-piston
clearance with the following for-
mula.
<Limit>
Piston pin-to-piston clearance =
0.50
Inside diameter (piston) "b" -
mm
Outside diameter (piston pin)
(0.020
"a"
in)
d. If out of specification, replace the
0.80
piston.
mm
Piston pin-to-piston
(0.031
clearance:
in)
—
INSTALLING THE PISTON RING
AND PISTON
1. Install:
• Piston ring
Onto the piston.
• Be sure to install the piston rings so
that the manufacturer's marks or
numbers are located on the upper
side of the rings.
• Lubricate the piston and piston
rings liberally with engine oil.
2. Position:
• Top ring
• 2nd ring
• Oil ring
Offset the piston ring end gaps as
shown.
CYLINDER AND PISTON
0.002–0.022 mm
(0.0001–0.0009 in)
<Limit>:0.07 mm (0.003
in)
5-27
a. Top ring end
b. 2nd ring end
c. Oil ring end (upper)
d. Oil ring
e. Oil ring end (lower)
3. Install:
• Piston "1"
• Piston pin "2"
• Piston pin clip "3"
• Apply engine oil onto the piston pin
and piston.
• Be sure that the arrow mark "a" on
the piston points to the exhaust side
of the engine.
• Before installing the piston pin clip,
cover the crankcase with a clean
rag to prevent the piston pin clip
from falling into the crankcase.
• Install the piston pin clips with their
ends facing downward.
INSTALLING THE CYLINDER
1. Lubricate:
• Piston
• Piston ring
• Cylinder
Apply a liberal coating of engine oil.
2. Install:
• Dowel pin "1"
• O-ring "2"
Apply the lithium soap base grease
on the O-ring.
New