radiator YAMAHA YZ426F 2000 Owners Manual

CHAPTER 4
ENGINE
SEAT, FUEL TANK AND
SIDE COVERS
.......................................... 4-1
EXHAUST PIPE AND SILENCER
............ 4-3
RADIATOR
................................................ 4-4
CARBURETOR
......................................... 4-7
CAMSHAFTS
.......................................... 4-17
CYLINDER HEAD
................................... 4-24
VALVES AND VALVE SPRINGS
........... 4-27
CYLINDER AND PISTON
....................... 4-35
CLUTCH
.................................................. 4-41
OIL FILTER, WATER PUMP AND
CRANKCASE COVER (RIGHT)
............. 4-47
BALANCER
............................................ 4-53
OIL PUMP
............................................... 4-56
KICK AXLE AND SHIFT SHAFT
............ 4-60
CDI MAGNETO
....................................... 4-67
ENGINE REMOVAL
................................ 4-71
CRANKCASE AND CRANKSHAFT
....... 4-76
TRANSMISSION, SHIFT CAM,
SHIFT FORK
........................................... 4-85
CHAPTER 5
CHASSIS
FRONT WHEEL AND REAR WHEEL
...... 5-1
FRONT BRAKE AND REAR BRAKE
..... 5-10
FRONT FORK
......................................... 5-27
HANDLEBAR
.......................................... 5-40
STEERING
.............................................. 5-45
SWINGARM
............................................ 5-50
REAR SHOCK ABSORBER
................... 5- 57

1 - 1
GEN
INFO

DESCRIPTION
EC100000
GENERAL INFORMATION
EC110000
DESCRIPTION
1
Clutch lever
2
Decompression lever
3
Front brake lever
4
Throttle grip
5
Radiator cap
6
Fuel tank cap
7
Oil filler plug/dipstick
8
“ENGINE STOP” button
9
Kick starter
0
Fuel tank
A
Radiator
B
Coolant drain bolt
C
Rear brake pedal
D
Valve joint
E
Fuel cock
F
Cold starter knob
G
Hot starter knob (red)
H
Drive chain
I
Air cleaner
J
Shift pedal
K
Front fork
NOTE:

l
The machine you have purchased may differ
slightly from those shown in the following.
l
Designs and specifications are subject to
change without notice.
1
1

1 - 6
GEN
INFO
SPECIAL TOOLS
EC140001
SPECIAL TOOLS
The proper special tools are necessary for complete and accurate tune-up and assembly. Using the
correct special tool will help prevent damage caused by the use of improper tools or improvised
techniques. The shape and part number used for the special tool differ by country, so two types are
provided. Refer to the list provided to avoid errors when placing an order.
NOTE:
lFor U.S.A. and Canada, use part number starting with “YM-” or “YU-”.
lFor others, use part number starting with “90890-”.
Part number Tool name/How to use Illustration
YU-01135-A, 90890-01135
YM-01305, 90890-01305Crankcase separating tool
Crankcase separating bolt
These tools are used to split the crankcase as well as
remove the crankshaft from either case.YU-01135-A
YM-0130590890-01135
90890-01305
YU-01235, 90890-01235 Rotor holding tool
This tool is used when loosening or tightening the fly-
wheel magneto securing nut.YU-01235 90890-01235
YU-03097, 90890-01252
YU-01256Dial gauge and stand
Stand
These tools are used to set the ignition timing.YU-03097
YU-0125690890-01252
YU-90050, 90890-01274
YU-90050, 90890-01275
YU-91044, 90890-04081
YU-90062, 90890-01277Crankcase installing tool
Pot
Bolt
Spacer
Adapter
These tools are used to install the crankshaft.YU-90050
YU-90062
YU-9104490890-01274
90890-01275
90890-01277
90890-04081
YU-01304, 90890-01304 Piston pin puller
This tool is used to remove the piston pin.YU-01304 90890-01304
YU-24460-1, 90890-01325
YU-33984, 90890-01352Radiator cap tester
Adapter
These tools are used for checking the cooling sys-
tem.YU-24460-01
YU-3398490890-01325
90890-01352
YM-01189, 90890-01189 Flywheel puller
This tool is used to remove the flywheel magneto.YM-01189 90890-01189

SPEC

2 - 9
MAINTENANCE SPECIFICATIONS
Lubrication system:
Oil filter type Wire mesh type ----
Oil pump type Trochoid type ----
Tip clearance “A” or “B” 0.07 ~ 0.12 mm
(0.0028 ~ 0.0047 in)0.15 mm
(0.006 in)
Side clearance 0.03 ~ 0.08 mm
(0.0012 ~ 0.0031 in)0.15 mm
(0.006 in)
Bypass valve setting pressure 40 ~ 80 kPa (0.4 ~ 0.8 kg/cm
2

,
5.69 ~ 11.38 psi)----
Cooling:
Radiator core size
Width 117.8 mm (4.6 in) ----
Height 260 mm (10.2 in) ----
Thickness 32 mm (1.26 in) ----
Radiator cap opening pressure110 kPa (1.1 kg/cm
2

, 15.6 psi)----
Radiator capacity (total) 0.76 L (0.67 lmp qt, 0.80 US qt) ----
Water pump
Type Single-suction centrifugal pump ----Item Standard Limit

SPEC

2 - 11
MAINTENANCE SPECIFICATIONS
Part to be tightened Thread size Q’tyTightening torque
Nm m·kg ft·lb
Spark plug M10
´
1.0 1 13 1.3 9.4
Camshaft cap M6
´
1.0 10 10 1.0 7.2
Cylinder head (stud bolt) M6
´
1.0 2 7 0.7 5.1
M8
´
1.25 3 15 1.5 11
(bolt) M10
´
1.25 4 44 4.4 32
(nut) M6
´
1.0 2 10 1.0 7.2
M8
´
1.25 2 20 2.0 14
Cylinder head cover M6
´
1.0 2 10 1.0 7.2
Cylinder M6
´
1.0 1 10 1.0 7.2
Timing chain tensioner M6
´
1.0 2 10 1.0 7.2
Tensioner cap bolt M6
´
1.0 1 7 0.7 5.1
Timing chain guide (rear) M6
´
1.0 2 10 1.0 7.2
Decompression shaft M6
´
1.0 1 7 0.7 5.1
Decompression cable guide M6
´
1.0 1 10 1.0 7.2
Exhaust pipe (nut) M8
´
1.25 1 24 2.4 17
(bolt) M8
´
1.25 1 24 2.4 17
Silencer M8
´
1.25 2 35 3.5 25
Silencer clamp M8
´
1.25 1 20 2.0 14
Exhaust pipe protector M6
´
1.0 3 10 1.0 7.2
Clamp (air cleaner joint) M5
´
0.8 1 3 0.3 2.2
Clamp (carburetor joint) M4
´
0.7 1 3 0.3 2.2
Air filter joint clamp M6
´
1.0 1 3 0.3 2.2
Throttle cable cover M5
´
0.8 1 4 0.4 2.9
Air filter element M6
´
1.0 1 2 0.2 1.4
Radiator panel (upper) M6
´
1.0 2 10 1.0 7.2
Radiator M6
´
1.0 6 10 1.0 7.2
Radiator hose clamp M6
´
1.0 8 2 0.2 1.4
Impeller M8 ´ 1.25 1 14 1.4 10
Water pump housing cover M6 ´ 1.0 3 10 1.0 7.2
Coolant drain bolt M6 ´ 1.0 1 10 1.0 7.2
Oil pump cover M5 ´ 0.8 1 4 0.4 2.9
Oil pump M6 ´ 1.0 3 10 1.0 7.2
Engine oil drain bolt (oil filter) M6 ´ 1.0 1 10 1.0 7.2
Oil filter cover M6 ´ 1.0 2 10 1.0 7.2
Oil delivery pipe 1 M10 ´ 1.25 1 20 2.0 14
M8 ´ 1.25 2 18 1.8 13
Oil hose clamp – 2 2 0.2 1.4
Clutch cover M6 ´ 1.0 7 10 1.0 7.2
Crankcase cover (right) M6 ´ 1.0 10 10 1.0 7.2
Crankcase cover (left) M6 ´ 1.0 8 10 1.0 7.2
Crankcase M6 ´ 1.0 12 12 1.2 8.7
Oil drain bolt (crankcase) M12 ´ 1.5 1 20 2.0 1.4
Oil drain bolt (frame) M8 ´ 1.25 1 23 2.3 17

SPEC
2 - 16
MAINTENANCE SPECIFICATIONS
NOTE:
- marked portion shall be checked for torque tightening after break-in or before each race.Part to be tightened Thread size Q’tyTightening torque
Nm m·kg ft·lb
Rear brake reservoir tank and frame M6 ´ 1.0 1 10 1.0 7.2
Rear brake hose union bolt (caliper) M10 ´ 1.25 1 30 3.0 22
Rear brake hose union bolt (master cylinder)M10 ´ 1.25 1 30 3.0 22
Rear wheel axle and nut M20 ´ 1.5 1 125 12.5 90
Driven sprocket and wheel hub M8 ´ 1.25 6 42 4.2 30
Nipple (spoke) – 72 3 0.3 2.2
Disc cover and rear brake caliper M6 ´ 1.0 2 7 0.7 5.1
Protector and rear brake caliper M6 ´ 1.0 2 7 0.7 5.1
Engine mounting:
Engine bracket and frame M8 ´ 1.25 7 34 3.4 24
Engine and frame (front) M10 ´ 1.25 1 69 6.9 50
Engine and frame (upper) M10 ´ 1.25 1 55 5.5 40
Engine and frame (lower) M10 ´ 1.25 1 69 6.9 50
Pivot shaft and nut M16 ´ 1.5 1 85 8.5 61
Relay arm and swingarm M14 ´ 1.5 1 80 8.0 58
Relay arm and connecting rod M14 ´ 1.5 1 80 8.0 58
Connecting rod and frame M14 ´ 1.5 1 80 8.0 58
Rear shock absorber and frame M10 ´ 1.25 1 56 5.6 40
Rear shock absorber and relay arm M10 ´ 1.25 1 53 5.3 38
Rear frame and frame M8 ´ 1.25 3 26 2.6 19
Swingarm and brake hose holder M5 ´ – 4 4 0.4 2.9
Drive chain tensioner mounting M8 ´ 1.25 2 19 1.9 13
Chain support and swingarm M6 ´ 1.0 3 7 0.7 5.1
Seal guard and swingarm M5 ´ 0.8 4 4 0.4 2.9
Fuel tank mounting M6 ´ 1.0 2 10 1.0 7.2
Fuel tank and fuel cock M6 ´ 1.0 2 7 0.7 5.1
Fuel tank and seat set bracket M6 ´ 1.0 1 7 0.7 5.1
Fuel tank and hooking screw (fitting band) M6 ´ 1.0 1 7 0.7 5.1
Fuel tank and fuel tank bracket M6 ´ 1.0 4 7 0.7 5.1
Seat mounting M8 ´ 1.25 2 23 2.3 17
Side cover mounting M6 ´ 1.0 2 7 0.7 5.1
Air scoop and fuel tank M6 ´ 1.0 4 4 0.4 2.9
Air scoop and radiator panel (lower) M6 ´ 1.0 2 4 0.4 2.9
Rear fender mounting M6 ´ 1.0 4 7 0.7 5.1

2 - 22
SPEC

CABLE ROUTING DIAGRAM
ð
Fasten the TPS lead under the
coupler to the frame with a plas-
tic locking tie.
ñPass the carburetor breather
hose and overflow hose
between the connecting rod and
cross tube (frame).
÷Fasten the neutral switch lead
and oil hose together with a
plastic locking tie and cut off the
tie end.
öFasten the cylinder head
breather hose and neutral switch
lead to the frame with a plastic
locking tie.
¯Fasten the neutral switch lead to
the frame with a plastic band.¸Fasten the cylinder head
breather hose with the hose
holder.
ÎPass the clutch cable through
the cable guide.
åFasten the neutral switch lead
and CDI magneto lead
together with a plastic band.
êPass the clutch cable on the
inside the cylinder head
breather hose.
æPass the cylinder head
breather hose along the inner
side of the radiator pipe.
èPass the radiator breather
hose from the right side of the
frame to the left side, over
radiator pipe 1, along the innerside of radiator hose 4 and
the radiator, and between the
lower engine bracket, crank-
case, oil hose and the frame.
×Pass the clutch cable
between the frame and radia-
tor and over the lower boss on
the radiator.
ãPass the neutral switch lead
and CDI magneto lead over
the middle radiator mounting
boss. Then, pass the decom-
pression cable under the mid-
dle radiator mounting boss
and along the left side of the
neutral switch lead and CDI
magneto lead.

2 - 24
SPECCABLE ROUTING DIAGRAM
1Clamp
2Ignition coil
3High tension cord
4CDI unit
5CDI unit band
6Throttle cable (pull)
7Throttle cable (return)
8Radiator (left)
9Radiator breather hose
0Radiator (right)
ACDI unit stay (frame)Fasten the ignition coil lead to the
frame with a plastic band.
õFasten the ignition coil and
ground lead to the frame with the
bolt.
‚Pass the ignition coil lead (in the
sub wire harness) so that it does
not contact the carburetor and
rear shock absorber and connect
it with the lead from the ignition
coil on the inside of the frame.
ëPass the throttle cables over the
high tension cord.
äPass the throttle cables along the
outer side of the CDI unit leads.
ìFasten the CDI unit leads to the
frame with a plastic locking tie.
íPass the throttle cables between
the top radiator mounting boss
and middle radiator mounting
boss.îPass the CDI unit leads over the
top radiator mounting boss.
éCross the pull and return throttle
cables before the radiator.
ïPass the throttle cables through
cable guide on the frame.
ðPass the radiator breather hose
between the frame and the radia-
tor without pinching it.
ñPass the radiator breather hose
behind the decompression cable.
÷Insert the CDI unit band over the
CDI unit stay (frame) as far as
possible.

3 - 2
INSP
ADJ

MAINTENANCE INTERVALS
SHIFT FORK, SHIFT CAM, GUIDE BAR
Inspect
c
Inspect wear
ROTOR NUT
Retighten
cc
MUFFLER
Inspect
Clean
Replace
cc
cc
* Whichever comes first
CRANK
Inspect and clean
cc
CARBURETOR
Inspect, adjust and clean
cc
When using a high-pres-
sure washer, make sure
that water does not enter
the accelerator pump.
SPARK PLUG
Inspect and clean
Replace
cc
c
DRIVE CHAIN
Lubricate, slack, alignment
Replace
cc
c
Use chain lube
Chain slack: 40~50 mm
(1.6~2.0 in)
COOLING SYSTEM
Check coolant level and leakage
Check radiator cap operation
Replace coolant
Inspect hoses
cc
cc
c
Every two years
OUTSIDE NUTS AND BOLTS
Retighten
cc
Refer to “STARTING AND
BREAK-IN” section in the
CHAPTER 1.
AIR FILTER
Clean and lubricate
Replace
cc
c
Use foam air-filter oil
OIL STRAINER (frame)
Clean
c
FRAME
Clean and inspect
cc
FUEL TANK, COCK
Clean and inspect
cc
BRAKES
Adjust lever position and pedal height
Lubricate pivot point
Check brake disc surface
Check fluid level and leakage
Retighten brake disc bolts, caliper
bolts, master cylinder bolts and union
bolts
Replace pads
Replace brake fluid
c
c
c
c
cc
c
c
c
c
c
c
Every one year
FRONT FORKS
Inspect and adjust
Replace oil
Replace oil seal
c
cc
c
c
Suspension oil “01” ItemAfter
break-inEvery
race
Every
third
(or
500 km)Every
fifth
(or
1,000 km)
As re-
quiredRemarks
3

3 - 4
INSP
ADJ

PRE-OPERATION INSPECTION AND MAINTENANCE
EC320000
PRE-OPERATION INSPECTION AND MAINTENANCE
Before riding for break-in operation, practice or a race, make sure the machine is in good operating
condition.
Before using this machine, check the following points.
EC321000
GENERAL INSPECTION AND MAINTENANCE
Item Routine Page
CoolantCheck that coolant is filled up to the radiator filler cap.
Check the cooling system for leakage.P.3-5 ~ 9
FuelCheck that a fresh gasoline is filled in the fuel tank. Check the
fuel line for leakage.P.1-12
Engine oilCheck that the oil level is correct. Check the crankcase and
frame oil line for leakage.P.3-13 ~ 17
Gear shifter and clutchCheck that gears can be shifted correctly in order and that the
clutch operates smoothly.P.3-9
Throttle grip/HousingCheck that the throttle grip operation and free play are correctly
adjusted. Lubricate the throttle grip and housing, if necessary.P.3-10 ~ 11
Brakes Check the play of front brake and effect of front and rear brake. P.3-24 ~ 30
ChainCheck chain slack and alignment. Check that the chain is lubri-
cated properly.P.3-31 ~ 33
WheelsCheck for excessive wear and tire pressure. Check for loose
spokes and have no excessive play.P.3-41 ~ 42
SteeringCheck that the handlebar can be turned smoothly and have no
excessive play.P.3-42 ~ 43
Front forks and rear shock
absorberCheck that they operate smoothly and there is no oil leakage. P.3-33 ~ 40
Cables (wires)Check that the clutch and throttle cables move smoothly. Check
that they are not caught when the handlebars are turned or
when the front forks travel up and down.—
Muffler Check that the muffler is tightly mounted and has no cracks. P.4-3
Sprocket Check that the driven sprocket tightening bolt is not loose. P.3-31
Lubrication Check for smooth operation. Lubricate if necessary. P.3-44
Bolts and nuts Check the chassis and engine for loose bolts and nuts. P.1-17
Lead connectorsCheck that the CDI magneto, CDI unit, and ignition coil are con-
nected tightly.P.1-5
SettingsIs the machine set suitably for the condition of the racing course
and weather or by taking into account the results of test runs
before racing? Are inspection and maintenance completely
done?P.7-1 ~ 21