engine oil YAMAHA YZ426F 2001 Service Manual

4 - 77
ENGENGINE REMOVAL
EC4M0000
ENGINE REMOVAL
Extent of removal Order Part name Q’ty Remarks
ENGINE REMOVAL
Preparation for removal Hold the machine by placing the
suitable stand under the frame.
WARNING
Support the machine securely so there is no
danger of it falling over.
Seat and fuel tank Refer to “SEAT, FUEL TANK AND SIDE
COVERS” section.
Carburetor Refer to “CARBURETOR” section.
Exhaust pipe and silencer Refer to “EXHAUST PIPE AND
SILENCER” section.
Clutch cable Disconnect at engine side.
Decompression cable and guide Disconnect at engine side.
Radiator Refer to “RADIATOR” section.
Shift pedal Refer to “CDI MAGNETO” section.
Cylinder head breather hose and
oil tank breather hoseRefer to “CAMSHAFTS” section.
Drain the engine oil Refer to “ENGINE OIL REPLACEMENT”
section in the CHAPTER 3.
Spark plug cap
Disconnect the CDI magneto lead.

4 - 78
ENGENGINE REMOVAL
Extent of removal:1 Engine removal
Extent of removal Order Part name Q’ty Remarks
1 Engine skidplate 1
2 Neutral switch 1
3 Oil hose 2
4 Chain cover 1
5 Nut (drive sprocket) 1
Refer to “REMOVAL POINTS”. 6 Lock washer 1
7 Drive sprocket 1
8 Clip 1
9 Bolt (brake pedal) 1
10 Brake pedal 1
11 Engine upper bracket (right) 1
12 Engine upper bracket (left) 1
13 Engine lower bracket 2
14 Engine mounting bolt 3
15 Pivot shaft 1
Refer to “REMOVAL POINTS”.
16 Engine 1
1

4 - 81
ENGENGINE REMOVAL
2. Install:
lLock washer 1
lNut (drive sprocket) 2
NOTE:
Tighten the nut while applying the rear brake.
New
T R..75 Nm (7.5 m · kg, 54 ft · lb)
3. Bend the lock washer tab to lock the nut.
4. Install:
lChain guide
lChain cover 1
lScrew (chain cover) 2
T R..8 Nm (0.8 m · kg, 5.8 ft · lb)
5. Install:
lOil hose 1
lBolt (oil hose) 2
T R..10 Nm (1.0 m · kg, 7.2 ft · lb)
6. Install:
lSpring 1
lPin 2
lNeutral switch 3
lBolt (neutral switch) 4
T R..4 Nm (0.4 m · kg, 2.9 ft · lb)

4 - 86
ENGCRANKCASE AND CRANKSHAFT
Crankshaft
1. Remove:
lCrankshaft 1
Use the crankcase separating tool 2.
CAUTION:
Do not use a hammer to drive out the
crankshaft.
Crankshaft bearing
1. Remove:
lBearing 1
NOTE:
lRemove the bearing from the crankcase by
pressing its inner race.
lDo not use the removed bearing.
Crankcase separating tool:
YU-1135-A/90890-01135
INSPECTION
Timing chain and timing chain guide
1. Inspect:
lTiming chain
Cracks/stiff ® Replace the timing chain
and camshaft sprocket as a set.
2. Inspect:
lTiming chain guide
Wear/damage ® Replace.
EC4N4101
Crankcase
1. Inspect:
lContacting surface a
Scratches ® Replace.
lEngine mounting boss b, crankcase
Cracks/damage ® Replace.
2. Inspect:
lBearing
Rotate inner race with a finger.
Rough spot/seizure ® Replace.
3. Inspect:
lOil seal
Wear/damage ® Replace.

4 - 90
ENGCRANKCASE AND CRANKSHAFT
6. Tighten:
lHose guide 1
lClutch cable holder 2
lBolt (crankcase)
NOTE:
Tighten the crankcase tightening bolts in
stage, using a crisscross pattern.
T R..12 Nm (1.2 m · kg, 8.7 ft · lb)
7. Install:
lOil delivery pipe
lO-ring
lBolt (oil delivery pipe)
8. Install:
lTiming chain
lTiming chain guide (rear)
lBolt (timing chain guide)
9. Remove:
lSealant
Forced out on the cylinder mating sur-
face.
10. Apply:
lEngine oil
To the crank pin, bearing and oil deliv-
ery hole.
11. Check:
lCrankshaft and transmission operation.
Unsmooth operation ® Repair.
New
T R..10 Nm (1.0 m · kg, 7.2 ft · lb)
T R..10 Nm (1.0 m · kg, 7.2 ft · lb)

4 - 95
ENG

TRANSMISSION, SHIFT CAM AND SHIFT FORK
5. Install:
l
Shift fork 1 (L)
1

l
Shift fork 2 (C)
2

l
Shift fork 3 (R)
3

l
Shift cam
4

To main axle and drive axle.
NOTE:

l
Apply the molybdenum disulfide oil on the
shift fork grooves.
l
Mesh the shift fork #1 (L) with the 4th wheel
gear
5
and #3 (R) with the 5th wheel gear
7
on the drive axle.
l
Mesh the shift fork #2 (C) with the 3rd pinion
gear
6
on the main axle.
6. Install:
l
Transmission assembly
1

To crankcase (left)
2
.
NOTE:

Apply the engine oil on the bearings and guide
bars.
7. Check:
l
Shifter operation
l
Transmission operation
Unsmooth operation
®
Repair.

5 - 1
CHAS
EC500000
CHASSIS
EC590000
FRONT WHEEL AND REAR WHEEL
EC598000
FRONT WHEEL
FRONT WHEEL AND REAR WHEEL
Extent of removal:1 Front wheel removal2 Wheel bearing removal
3 Break disc removal
Extent of removal Order Part name Q’ty Remarks
Preparation for removalFRONT WHEEL REMOVAL
Hold the machine by placing the
suitable stand under the engine.
WARNING
Support the machine securely so there is nodanger of it falling over.
1 Hose cover 1
2 Bolt (brake hose holder) 2 Only loosening.
3 Bolt (axle holder) 4 Only loosening.
4 Nut (front wheel axle) 1
5 Front wheel axle 1
6 Front wheel 1
7 Collar 2
8 Oil seal 2
9 Bearing 2 Refer to “REMOVAL POINTS”.
10Brake disk
1
2
31
3




5

5 - 2
CHAS

EC598100
REAR WHEEL
Extent of removal:
1
Rear wheel removal
2
Wheel bearing removal
3
Break disc removal
Extent of removal Order Part name Q’ty Remarks
Preparation for removal
REAR WHEEL REMOVAL
Hold the machine by placing the
suitable stand under the engine.
WARNING

Support the machine securely so there is no
danger of it falling over.
1 Nut (rear wheel axle) 1
2 Rear wheel axle 1
3 Chain puller 2
4 Rear wheel 1 Refer to “REMOVAL POINTS”.
5 Collar 2
6 Driven sprocket 1
7 Oil seal 2
8 Circlip 1
9 Bearing 2 Refer to “REMOVAL POINTS”.
10Brake disk
1
2
31
3

FRONT WHEEL AND REAR WHEEL

6 - 1
–+ELECELECTRICAL COMPONENTS AND WIRING DIAGRAM
EC600000
ELECTRICAL
EC610000
ELECTRICAL COMPONENTS AND WIRING DIAGRAM
EC611000
ELECTRICAL COMPONENTS
1“ENGINE STOP” button
2TPS (throttle position sensor)
3Neutral switch
4CDI magneto
5Ignition coil
6Spark plug
7CDI unitCOLOR CODE
B...................... Black
Br .................... Brown
G ..................... Green
L ...................... Blue
O ..................... Orange
P...................... Pink
R ..................... Red
EC612000
WIRING DIAGRAM
7
15
6
2 3 4
LY
BYL
B/LL
G
P
W
R
Y
B
G
BR PBrWG
RB Br WP
R/W WL/W SbW R/W Sb L/WY
B/LL Sb B OY
LB/L B OSbSb
L/WR/W
WSb
B/L
B/WB/W
B/WB/W
Br
BB
LBBY
O
Sb .................... Sky blue
W ..................... White
Y ...................... Yellow
B/L ................... Black/Blue
B/W .................. Black/White
L/W .................. Blue/White
R/W .................. Red/White




6

–+ELEC
6 - 2
MAP-CONTROLLED CDI UNIT
MAP-CONTROLLED CDI UNIT
A map-controlled, CDI ignition system is used in the YZ426F.
The microcomputer in the CDI unit detects the engine speed and throttle position, thus determining
the optimum ignition timing through the entire operating range. In this way, quick throttle response
can be achieved according to various riding conditions.
CDI unit
Throttle position sensor
Pickup coil CDI magneto rotorIgnition coil
nFunction of Component
Component Function
TPS
(throttle position sensor)Detects throttle valve opening and inputs it into the computer in the
CDI unit as a throttle opening signal.
Pickup coil Detects signal rotor revolutions and inputs them into the computer in
the CDI unit as engine revolution signals.
CDI unit The signals of the TPS and pickup coil sensor are analyzed by the
computer in the CDI unit, which then adjusts ignition timing for the
operation requirements.
nPrincipal of 3-Dimensional Control
Conventionally, ignition timing was controlled only
by engine revolutions (2-dimensional control).
However, ignition timing needs advancement also
by engine load. Thus, accurate ignition timing can
be determined by adding throttle opening to deter-
mine ignition timing (3-dimensional control).
3-D Image Map of Ignition Timing
(different from actual characteristics)
Revolutions
Ignition timing
Throttle opening