Yamaha 2011 WR250FA Owner's Service Manual page 173

CHECKING THE PISTON PIN
1. Inspect:
• Piston pin
Blue discoloration/grooves → Replace, 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 (piston) "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 formula.
Piston pin-to-piston clearance = Inside di-
ameter (piston) "b" - Outside diameter
(piston pin) "a"
d. If out of specification, replace the piston.
Piston pin-to-piston clearance:
0.002–0.022 mm (0.0001–0.0009 in)
<Limit>:0.07 mm (0.003 in)
CYLINDER AND PISTON
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.
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"
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