engine YAMAHA YZ85 2003 Service Manual

4 - 1
ENG
EC400000
ENGINE
SEAT, FUEL TANK AND SIDE COVERS
5PA40010
Extent of removal:
1 Seat removal
2 Fuel tank removal
3 Side covers removal
4 Number plate removal
Extent of removal Order Part name Q’ty Remarks
Preparation for removalSEAT, FUEL TANK AND SIDE
COVERS REMOVAL
Turn the fuel cock to “OFF”.
Disconnect the fuel hose.
1Seat 1
2 Air scoop 1
3 Bolt (fuel tank) 2
4 Fuel tank 1
5 Left side cover 1
6 Right side cover 1
7 Number plate 1
13
4
2
3
SEAT, FUEL TANK AND SIDE COVERS

4 - 4
ENGRADIATOR
EC456000
HANDLING NOTE
WARNING
Do not remove the radiator cap when the
engine and radiator are hot. Scalding hot
fluid and steam may be blown out under
pressure, which could cause serious
injury.
When the engine has cooled, open the radi-
ator cap by the following procedure:
Place a thick rag, like a towel, over the radi-
ator cap, slowly rotate the cap counter-
clockwise to the detent. This procedure
allows any residual pressure to escape.
When the hissing sound has stopped,
press down on the cap while turning coun-
terclockwise and remove it.
EC454000
INSPECTION
Radiator
1. Inspect:

Radiator core 1
Obstruction → Blow out with compressed
air through rear of the radiator.
Bent fin → Repair or replace.
5PA40040
EC455000
ASSEMBLY AND INSTALLATION
Radiator
1. Install:

Radiator breather hose 1
To radiator 2.
5PA40050
2. Install:

Radiator 1

Bolt (radiator) 2
5PA40060

4 - 14
ENGCARBURETOR AND REED VALVE
9. Install:

Mixing chamber top 1

Screw (mixing chamber top) 2
To carburetor 3.
NOTE:

Pass the throttle cable in front of the carbure-
tor breather hoses.

After installing, check the throttle grip for
smooth movement.5PA40350
Carburetor installation
1. Install:

Carburetor 1
NOTE:
Install the projection between the carburetor
joint slots.
5PA40360
2. Tighten:

Screw (air filter joint) 1

Screw (carburetor joint) 2
5PA40370
3. Clamp:

Carburetor breather hose 1

Overflow hose 2
Refer to “CABLE ROUTING DIAGRAM”
section in the CHAPTER 2.
5PA40380
4. Adjust:

Engine idling speed
Refer to “ENGINE IDLING SPEED
ADJUSTMENT” section in the CHAPTER 3.

4 - 23
ENG
NOTE:
When you purchase a cylinder, you cannot
designate its size. Choose the piston that
matches the above chart.
ASSEMBLY AND INSTALLATION
Piston ring and piston
1. Install:

Piston ring 1
NOTE:

Take care not to scratch the piston or dam-
age the piston ring.

Align the piston ring gap with the pin 2.

After installing the piston ring, check the
smooth movement of it.
5PA40620
2. Install:

Gasket (cylinder) 1

Small end bearing 2

Dowel pin 3
NOTE:

Apply the engine oil on the bearing (crank-
shaft and connecting rod) and connecting
rod big end washers.

Install the gasket with the seal print side
toward the crankcase.
5PA40630
CYLINDER HEAD, CYLINDER AND PISTON

4 - 24
ENG
3. Install:

Piston 1

Piston pin 2

Piston pin clip 3
NOTE:

The arrow a on the piston dome must point
to exhaust side.

Before installing the piston pin clip, cover the
crankcase with a clean rag to prevent the
piston pin clip from falling into the crankcase
cavity.
CAUTION:
Do not allow the clip open ends to meet the
piston pin slot b.
5PA40640
5PA40650
Cylinder head and cylinder
1. Apply:

Engine oil
To piston 1, piston ring 2 and cylinder
surface.
2. Install:

Cylinder 1
CAUTION:
Make sure the piston ring is properly posi-
tioned. Install the cylinder with one hand
while compressing the piston ring with the
other hand.
NOTE:
After installing, check the smooth movement of
the piston.
5PA40660
5PA40670
3. Install:

Nut (cylinder) 1
NOTE:
Tighten the nuts in stage, using a crisscross
pattern.
5PA40680
T R..28 Nm (2.8 m · kg, 20 ft · lb)
CYLINDER HEAD, CYLINDER AND PISTON

4 - 26
ENGCLUTCH AND PRIMARY DRIVEN GEAR
EC490000
CLUTCH AND PRIMARY DRIVEN GEAR
EC498000
CLUTCH PLATE AND FRICTION PLATE
5PA40720
Extent of removal:
1 Clutch plate and friction plate removal
Extent of removal Order Part name Q’ty Remarks
CLUTCH PLATE AND FRIC-
TION PLATE REMOVAL
Preparation for removal Drain the transmission oil. Refer to “TRANSMISSION OIL
REPLACEMENT” section in the CHAP-
TER 3.
Clutch cable Disconnect at engine side.
1 Clutch cover 1
2 Bolt (clutch spring) 5
3 Clutch spring 5
4 Pressure plate 1
5 Friction plate 7
6 Clutch plate 6
1

4 - 38
ENG
2. Install:

Spring guide 1
NOTE:
Slide the spring guide into the kick shaft, make
sure the groove a in the spring guide fits on
the stopper of the torsion spring.
5PA41120
3. Install:

Kick shaft assembly 1
NOTE:

Apply the transmission oil on the kick shaft.

Apply the lithium soap base grease on the
kick shaft stopper.

Slide the kick shaft assembly into the crank-
case, make sure the clip 2 and kick shaft
stopper a fit into their home positions b, c.5PA41130
4. Hook:

Torsion spring 1
NOTE:
Turn the torsion spring clockwise and hook
into the proper hole a in the crankcase.
5PA41140
Kick idle gear
1. Install:

Washer 1

Kick idle gear 2

Circlip 3
NOTE:

Apply the transmission oil on the kick idle
gear inner circumference.

Install the kick idle gear with its groove a
facing the engine.
5PA41150
KICK SHAFT, SHIFT SHAFT AND PRIMARY DRIVE GEAR

4 - 40
ENG
6. Install:

Right crankcase cover 1
NOTE:
Mesh the impeller shaft gear 2 with primary
drive gear 3.
5PA41200
7. Install:

Bolt (right crankcase cover) 1

Copper washer (oil drain bolt) 2

Oil drain bolt 3

Copper washer (coolant drain bolt)
4

Coolant drain bolt 5
NOTE:
Tighten the bolts in stage, using a crisscross
pattern.
5PA41210
T R..10 Nm (1.0 m · kg, 7.2 ft · lb)
T R..10 Nm (1.0 m · kg, 7.2 ft · lb)
T R..10 Nm (1.0 m · kg, 7.2 ft · lb)
8. Install:

Kickstarter crank 1

Washer 2

Bolt (kickstarter crank) 3
NOTE:
Install the kickstarter crank closest to but not con-
tacting the pillar tube 4 and exhaust pipe 5.
5PA41220
T R..10 Nm (1.0 m · kg, 7.2 ft · lb)
9. Install:

Shift pedal 1

Bolt (shift pedal) 2
NOTE:
Install the shift pedal with the bottom of the
pedal outer diameter a as close to the center
of the engine mounting bolt 3 as possible.
5PA41230
T R..10 Nm (1.0 m · kg, 7.2 ft · lb)
KICK SHAFT, SHIFT SHAFT AND PRIMARY DRIVE GEAR

4 - 49
ENG
EC4M0000
ENGINE REMOVAL
5PA41490
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.
Drain the coolant. Refer to “COOLANT REPLACEMENT”
section in the CHAPTER 3.
Seat and fuel tank Refer to “SEAT, FUEL TANK AND SIDE
COVERS” section.
Carburetor Refer to “CARBURETOR AND REED
VALVE” section.
Exhaust pipe and silencer Refer to “EXHAUST PIPE AND
SILENCER” section.
Clutch cable Disconnect at engine side.
Radiator hose 1 Disconnect at cylinder head side.
Radiator hose 2 Disconnect at water pump side.
Spark plug cap
Disconnect the CDI magneto
lead.
ENGINE REMOVAL

4 - 50
ENG
5PA41490
Extent of removal:
1 Engine removal
Extent of removal Order Part name Q’ty Remarks
1 Left crankcase cover 1
2 Nut (drive sprocket) 1
Refer to “REMOVAL POINTS”. 3 Lock washer 1
4 Drive sprocket 1
5 Engine mounting bolt 2
6 Pivot shaft 1
Refer to “REMOVAL POINTS”.
7Engine 1
1
ENGINE REMOVAL