2002 YAMAHA YZ85 engine

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

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:
lRadiator 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:
lRadiator breather hose 1
To radiator 2.
5PA40050
2. Install:
lRadiator 1
lBolt (radiator) 2
5PA40060

4 - 14
ENGCARBURETOR AND REED VALVE
9. Install:
lMixing chamber top 1
lScrew (mixing chamber top) 2
To carburetor 3.
NOTE:
lPass the throttle cable in front of the carbure-
tor breather hoses.
lAfter installing, check the throttle grip for
smooth movement.5PA40350
Carburetor installation
1. Install:
lCarburetor 1
NOTE:
Install the projection between the carburetor
joint slots.
5PA40360
2. Tighten:
lScrew (air filter joint) 1
lScrew (carburetor joint) 2
5PA40370
3. Clamp:
lCarburetor breather hose 1
lOverflow hose 2
Refer to “CABLE ROUTING DIAGRAM”
section in the CHAPTER 2.
5PA40380
4. Adjust:
lEngine 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:
lPiston ring 1
NOTE:
lTake care not to scratch the piston or dam-
age the piston ring.
lAlign the piston ring gap with the pin 2.
lAfter installing the piston ring, check the
smooth movement of it.
5PA40620
2. Install:
lGasket (cylinder) 1
lSmall end bearing 2
lDowel pin 3
NOTE:
lApply the engine oil on the bearing (crank-
shaft and connecting rod) and connecting
rod big end washers.
lInstall the gasket with the seal print side
toward the crankcase.
5PA40630
CYLINDER HEAD, CYLINDER AND PISTON

4 - 24
ENG
3. Install:
lPiston 1
lPiston pin 2
lPiston pin clip 3
NOTE:
lThe arrow a on the piston dome must point
to exhaust side.
lBefore 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:
lEngine oil
To piston 1, piston ring 2 and cylinder
surface.
2. Install:
lCylinder 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:
lNut (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:
lSpring 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:
lKick shaft assembly 1
NOTE:
lApply the transmission oil on the kick shaft.
lApply the lithium soap base grease on the
kick shaft stopper.
lSlide 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:
lTorsion spring 1
NOTE:
Turn the torsion spring clockwise and hook
into the proper hole a in the crankcase.
5PA41140
Kick idle gear
1. Install:
lWasher 1
lKick idle gear 2
lCirclip 3
NOTE:
lApply the transmission oil on the kick idle
gear inner circumference.
lInstall 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:
lRight crankcase cover 1
NOTE:
Mesh the impeller shaft gear 2 with primary
drive gear 3.
5PA41200
7. Install:
lBolt (right crankcase cover) 1
lCopper washer (oil drain bolt) 2
lOil drain bolt 3
lCopper washer (coolant drain bolt)
4
lCoolant 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:
lKickstarter crank 1
lWasher 2
lBolt (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:
lShift pedal 1
lBolt (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