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Yamaha YZ250F User Manual

Yamaha YZ250F
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VALVES AND VALVE SPRINGS
5-26
b. Install the valve into the cylinder head.
c. Press the valve through the valve guide and
onto the valve seat to make a clear impres-
sion.
d. Measure the valve seat width “c”.
TIP
Where the valve seat and the valve face are in
contact with each other, the blueing will have
been removed.
▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲
4. Lap:
Valve face
Valve seat
ECA1DX1018
NOTICE
This model uses titanium intake and ex-
haust valves.
Do not use the valves used for lapping the
valve seat. Always replace the valves used
for lapping with new ones.
TIP
When replacing the cylinder head, replace
also the valves with new ones without them.
When replacing the valves or the valve
guides, use new valves to lap the valve seats,
and then replace them with new valves.
▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼
a. Apply a coarse lapping compound “a” to the
valve face.
ECA13790
NOTICE
Do not let the lapping compound enter the
gap between the valve stem and the valve
guide.
b. Apply molybdenum disulfide oil onto the
valve stem.
c. Install the valve into the cylinder head.
d. Turn the valve until the valve face and the
valve seat are evenly polished, then clean
off all of the lapping compound.
TIP
While turning the valve lapper, tap and lap the
valve seat.
e. Apply a fine lapping compound to the valve
face, and repeat the above steps.
f. After every lapping step, be sure to clean off
all of the lapping compound from the valve
face and the valve seat.
g. Apply Mechanic’s blueing dye (Dykem) “b”
onto the valve face.
h. Install the valve into the cylinder head.
i. Press the valve through the valve guide and
onto the valve seat to make a clear impres-
sion.
j. Measure the valve seat width “c” again. If the
valve seat width is out of specification,
reface and lap the valve seat.
c

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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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