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Yamaha YZ250F User Manual

Yamaha YZ250F
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CYLINDER AND PISTON
5-32
b. If out of specification, rebore or replace the
cylinder, and replace the piston and the pis-
ton rings as a set.
c. Measure the piston outside diameter D “a” at
the measurement position H “b” with the mi-
crometer.
d. If out of specification, replace the cylinder,
the piston, and the piston rings as a set.
e. Calculate the piston-to-cylinder clearance
with the following formula.
f. If out of specification, replace the cylinder,
the piston, and the piston rings as a set.
▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲
EAS1SM5230
CHECKING THE PISTON RINGS
1. Measure:
Piston ring side clearance
Out of specification Replace the piston
and piston rings as a set.
TIP
Before measuring the piston ring side clear-
ance, eliminate any carbon deposits from the
piston ring grooves and piston rings.
2. Install:
Piston rings
TIP
Level the piston ring into the cylinder with the
piston.
3. Measure:
Piston ring end gap
Out of specification Replace the piston
ring.
TIP
The oil ring expander’s end gap cannot be
measured. If the oil ring rail’s gap is excessive,
replace all three oil rings.
Diameter D
76.955–76.970 mm (3.0297–
3.0303 in)
Measurement position H
9.0 mm (0.35 in)
Piston-to-cylinder clearance =
Cylinder bore - Piston diameter
Piston-to-cylinder clearance
0.030–0.055 mm (0.0012–0.0022
in)
Limit
0.15 mm (0.006 in)
b
a
Ring side clearance
0.030–0.065 mm (0.0012–0.0026
in)
Limit
0.120 mm (0.0047 in)
a. 10 mm (0.39 in)
Piston ring end gap
Top ring
End gap (installed)
0.15–0.25 mm (0.0059–0.0098 in)
Limit
0.50 mm (0.0197 in)
Oil ring
End gap (installed)
0.10–0.35 mm (0.0039–0.0138 in)

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Yamaha YZ250F Specifications

General IconGeneral
Displacement250cc
Bore x Stroke77.0 mm x 53.6 mm
Final DriveChain
Suspension / RearKYB® single shock; fully adjustable, 12.5-in travel
Brakes / FrontHydraulic single disc brake, 270mm
Brakes / RearHydraulic single disc brake, 240mm
Fuel Capacity1.6 gal
Engine TypeLiquid-cooled, DOHC, 4-stroke
Fuel DeliveryFuel injection
IgnitionTCI
Transmission5-speed; multiplate wet clutch
Suspension / FrontKYB® Speed-Sensitive System inverted fork; fully adjustable, 12.2-in travel
Tires / Front80/100-21

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