2002 YAMAHA YZ426F seats

3 - 1
INSP
ADJ

MAINTENANCE INTERVALS
EC300000
REGULAR INSPECTION AND ADJUSTMENTS
MAINTENANCE INTERVALS
The following schedule is intended as a general guide to maintenance and lubrication. Bear in mind
that such factors as weather, terrain, geographical location, and individual usage will alter the
required maintenance and lubrication intervals. If you are a doubt as to what intervals to follow in
maintaining and lubricating your machine, consult your Yamaha dealer.
ItemAfter
break-inEvery
race
Every
third
(or
500 km)Every
fifth
(or
1,000 km)
As re-
quiredRemarks
ENGINE OIL
Replace
●

●

OIL FILTER
Clean
●●

VALVES
Check the valve clearances.
Inspect
Replace
●

●

●

●
The engine must be cold.
Check the valve seats
and valve stems for wear.
VALVE SPRINGS
Inspect
Replace
●

●
Check the free length and
the tilt.
VALVE LIFTERS
Inspect
Replace
●

●
Check for scratches and
wear.
CAMSHAFTS
Inspect
Replace
●

●
Inspect the camshaft sur-
face.
CAMSHAFT SPROCKETS
Inspect
Replace
●

●
Check for wear on the
teeth and for damage.
PISTON
Inspect
Clean
Replace
●

●

●

●
Inspect crack
Remove carbon
PISTON RING
Inspect
Replace
●

●

●
Check ring end gap
PISTON PIN
Inspect
Replace
●

●

CYLINDER HEAD
Inspect and clean
●
Remove carbon
Change gasket
CYLINDER
Inspect and clean
Replace
●

●
Inspect score marks
Inspect wear
CLUTCH
Inspect and adjust
Replace
●

●

●
Inspect housing, friction
plate, clutch plate and
spring
TRANSMISSION
Inspect
Replace bearing
●

●

4 - 29
ENGCYLINDER HEAD
INSPECTION
Cylinder head
1. Eliminate:
Carbon deposits (from the combustion
chambers)
Use a rounded scraper.
NOTE:
Do not use a sharp instrument to avoid dam-
aging or scratching:
Spark plug threads
Valve seats
2. Inspect:
Cylinder head
Scratches/damage → Replace.
3. Measure:
Cylinder head warpage
Out of specification → Resurface.
Cylinder head warpage:
Less than 0.05 mm (0.002 in)
Warpage measurement and resurface-
ment steps:
Place a straightedge and a feeler gauge
across the cylinder head.
Use a feeler gauge to measure the
warpage.
If the warpage is out of specification,
resurface the cylinder head.
Place a 400 ~ 600 grit wet sandpaper on
the surface plate, and resurface the head
using a figure-eight sanding pattern.
NOTE:
To ensure an even surface rotate the cylin-
der head several times.

4 - 35
ENGVALVES AND VALVE SPRINGS
5. Measure:
Runout (valve stem)
Out of specification → Replace.
NOTE:
When installing a new valve always replace
the guide.
If the valve is removed or replaced always
replace the oil seal.
6. Eliminate:
Carbon deposits
(from the valve face and valve seat)
7. Inspect:
Valve seats
Pitting/wear → Reface the valve seat.
Runout limit:
0.01 mm (0.0004 in)
8. Measure:
Valve 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:
Apply Mechanic’s blueing dye (Dykem) b
to the valve face.
Install the valve into the cylinder head.
Press the valve through the valve guide
and onto the valve seat to make a clear
pattern.
Measure the valve seat width. Where the
valve seat and valve face made contact,
blueing will have been removed.
If the valve seat is too wide, too narrow, or
the seat is not centered, the valve seat
must be refaced.

4 - 38
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)
Blue Blue
Yellow Yellow
Purple Black
ab
ASSEMBLY AND INSTALLATION
1. Apply:
Molybdenum disulfide oil
Onto the valve stem and valve stem
seal.
2. Install:
Valves 1
Valve spring seats 2
Valve stem seals 3
Valve springs 4
Valve spring retainers 5
NOTE:
Make sure that each valve is installed in its
original place, also referring to the painted
color as follows.
Intake (middle) a: light blue
Intake (right/left) b: white
Exhaust: not paint
Install the valve springs with the larger pitch
c facing upward.
dSmaller pitch
New