2001 YAMAHA YZ250F oil

4 - 31
ENG
3. Install:
lWasher 1
lCable guide 2
lBolts [L=145 mm (5.71 in)] 3
lBolts [L=135 mm (5.31 in)] 4
lNuts 5
NOTE:
lApply the molybdenum disulfide grease on
the thread and contact surface of the bolts.
lFollow the numerical order shown in the illus-
tration. Tighten the bolts and nuts in two
stages.
T R..38 Nm (3.8 m · kg, 27 ft · lb)
T R..38 Nm (3.8 m · kg, 27 ft · lb)
T R..10 Nm (1.0 m · kg, 7.2 ft · lb)
4. Install:
lCopper washer 1
lOil delivery pipe 2
lUnion bolt (M8) 3
lUnion bolt (M10) 4
T R..18 Nm (1.8 m · kg, 13 ft · lb)
T R..20 Nm (2.0 m · kg, 14 ft · lb)
5. Install:
lDecompression cable guide 1
lBolt (decompression cable guide) 2
T R..10 Nm (1.0 m · kg, 7.2 ft · lb)
6. Install:
lRadiator pipe 1
lBolt (radiator pipe) 2
T R..10 Nm (1.0 m · kg, 7.2 ft · lb)
CYLINDER HEAD

4 - 36
ENGVALVES AND VALVE SPRINGS
5. Measure:
lRunout (valve stem)
Out of specification ® Replace.
NOTE:
lWhen installing a new valve always replace
the guide.
lIf the valve is removed or replaced always
replace the oil seal.
6. Eliminate:
lCarbon deposits
(from the valve face and valve seat)
7. Inspect:
lValve seat
Pitting/wear ® Reface the valve seat.
Runout limit:
0.01 mm (0.0004 in)
8. Measure:
lValve seat width a
Out of specification ® Reface the valve
seat.
Valve seat width:
Intake:
0.9 ~ 1.1 mm (0.0354 ~ 0.0433 in)
: 1.6 mm (0.0630 in)
Exhaust:
0.9 ~ 1.1 mm (0.0354 ~ 0.0433 in)
: 1.6 mm (0.0630 in)
Measurement steps:
lApply Mechanic’s blueing dye (Dykem) b
to the valve face.
lInstall the valve into the cylinder head.
lPress the valve through the valve guide
and onto the valve seat to make a clear
pattern.
lMeasure the valve seat width. Where the
valve seat and valve face made contact,
blueing will have been removed.
lIf the valve seat is too wide, too narrow, or
the seat is not centered, the valve seat
must be refaced.

4 - 37
ENGVALVES AND VALVE SPRINGS
9. Lap:
lValve face
lValve seat
NOTE:
After refacing the valve seat or replacing the
valve and valve guide, the valve seat and
valve face should be lapped.
Lapping steps:
lApply a coarse lapping compound to the
valve face.
CAUTION:
Do not let the compound enter the gap
between the valve stem and the guide.
lApply molybdenum disulfide oil to the
valve stem.
lInstall the valve into the cylinder head.
lTurn the valve until the valve face and
valve seat are evenly polished, then clean
off all of the compound.
NOTE:
For best lapping results, lightly tap the valve
seat while rotating the valve back and forth
between your hands.
lApply a fine lapping compound to the
valve face and repeat the above steps.
NOTE:
After every lapping operation be sure to
clean off all of the compound from the valve
face and valve seat.
lApply Mechanic’s blueing dye (Dykem) to
the valve face.
lInstall the valve into the cylinder head.
lPress the valve through the valve guide
and onto the valve seat to make a clear
pattern.
lMeasure the valve seat width again. If the
valve seat width is out of specification,
reface and relap the valve seat.

4 - 39
ENGVALVES AND VALVE SPRINGS
Combination of cylinder head and valve lifter
1. Combination:
For this combination, match the paint color
on the cylinder head with that on the valve
lifter according to the chart below.
NOTE:
When you purchase a cylinder head, you can-
not designate its size. Choose the valve lifter
that matches the above chart.Combination
Cylinder head mark
a (color)Valve lifter mark b
(color)
Red Red
Blue Blue
Yellow Yellow
Purple Black
ab
ASSEMBLY AND INSTALLATION
Valve and valve spring
1. Apply:
lMolybdenum disulfide oil
Onto the valve stem and valve stem
seal.
2. Install:
lValve 1
lValve spring seat 2
lValve stem seal 3
lValve spring 4
lValve spring retainer 5
To cylinder head.
NOTE:
lMake sure that each valve is installed in its
original place, also referring to the painted
color as follows.
Intake (middle) a: yellow
Intake (right/left) b: white
Exhaust: no paint
lInstall the valve springs with the larger pitch
c facing upward.
dSmaller pitch

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ENGVALVES AND VALVE SPRINGS
3. Install:
lValve cotter
NOTE:
While compressing the valve spring with a
valve spring compressor 1 install the valve
cotters.
4. To secure the valve cotters onto the
valve stem, lightly tap the valve tip with a
piece of wood.
CAUTION:
Hitting the valve tip with excessive force
could damage the valve.
Valve spring compressor:
YM-04019/90890-04019
5. Install:
lAdjusting pad 1
lValve lifter 2
NOTE:
lApply the molybdenum disulfied oil on the
valve stem end.
lApply the engine oil on the valve lifters.
lValve lifter must turn smoothly when rotated
with a finger.
lBe careful to reinstall valve lifters and pads
in their original place.

4 - 44
ENGCYLINDER AND PISTON
Piston ring
1. Measure:
lRing side clearance
Use a feeler gauge 1.
Out of specification ® Replace the pis-
ton and rings as a set.
NOTE:
Clean carbon from the piston ring grooves and
rings before measuring the side clearance.
2. Position:
lPiston ring
(in cylinder)
NOTE:
Insert a ring into the cylinder and push it
approximately 10 mm (0.39 in) into the cylin-
der. Push the ring with the piston crown so that
the ring will be at a right angle to the cylinder
bore.
a10 mm (0.39 in)
Side clearance:
Standard
Top ring0.030 ~ 0.065 mm
(0.0012 ~ 0.0026 in)0.12 mm
(0.005 in)
2nd ring0.020 ~ 0.055 mm
(0.0008 ~ 0.0022 in)0.12 mm
(0.005 in)
3. Measure:
lRing end gap
Out of specification ® Replace.
NOTE:
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 ring0.15 ~ 0.25 mm
(0.006 ~ 0.010 in)0.50 mm
(0.020 in)
2nd ring0.30 ~ 0.45 mm
(0.012 ~ 0.018 in)0.80 mm
(0.031 in)
Oil ring0.10 ~ 0.40 mm
(0.004 ~ 0.016 in)—

4 - 45
ENGCYLINDER AND PISTON
Piston pin
1. Inspect:
lPiston pin
Blue discoloration/grooves ® Replace,
then inspect the lubrication system.
2. Measure:
lPiston pin-to-piston clearance
ASSEMBLY AND INSTALLATION
Piston ring and piston
1. Install:
lPiston ring
Onto the piston.
NOTE:
lBe sure to install the piston rings so that the
manufacturer’s marks or numbers are
located on the upper side of the rings.
lLubricate the piston and piston rings liberally
with engine oil. Measurement steps:
lMeasure 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)
lMeasure the inside diameter (piston) b.
Inside diameter (piston):
16.002 ~ 16.013 mm
(0.6300 ~ 0.6304 in)
lCalculate the piston pin-to-piston clear-
ance with the following formula.
Piston pin-to-piston clearance =
Inside diameter (piston) b –
Outside diameter (piston pin) a
lIf out of specification, replace the piston.
Piston pin-to-piston clearance:
0.002 ~ 0.022 mm
(0.0001 ~ 0.0009 in)
: 0.07 mm (0.003 in)

4 - 46
ENGCYLINDER AND PISTON
2. Position:
lTop ring
l2nd ring
lOil ring
Offset the piston ring end gaps as
shown.
aTop ring end
b2nd ring end
cOil ring end (upper)
dOil ring
eOil ring end (lower)
3. Install:
lPiston 1
lPiston pin 2
lPiston pin clip 3
NOTE:
lApply engine oil onto the piston pin and pis-
ton.
lBe sure that the arrow mark a on the piston
points to the exhaust side of the engine.
lBefore installing the piston pin clip, cover the
crankcase with a clean rag to prevent the
piston pin clip from falling into the crankcase.
lInstall the piston pin clips with their ends fac-
ing downward.
45¡
135¡135¡
a
b ced
3New
Cylinder
1. Lubricate:
lPiston
lPiston ring
lCylinder
NOTE:
Apply a liberal coating of engine oil.
2. Install:
lDowel pin 1
lO-ring 2
NOTE:
Apply the lithium soap base grease on the O-
ring.