2004 YAMAHA YZ85 engine

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

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ENG
EC4M3000
REMOVAL POINTS
EC4F3100
Drive sprocket
1. Remove:

Nut (drive sprocket) 1

Lock washer 2
NOTE:

Straighten the lock washer tab.

Loosen the nut while applying the rear brake.5PA41510
2. Remove:

Drive sprocket 1

Drive chain 2
NOTE:
Remove the drive sprocket together with the
drive chain.
5PA41520
EC4M3301
Engine removal
1. Remove:

Pivot shaft 1
NOTE:
If the pivot shaft is pulled all the way out, the
swingarm will come loose. If possible, insert a
shaft of similar diameter into the other side of
the swingarm to support it.5PA41530
2. Remove:

Engine 1
From right side.
NOTE:
Make sure that the couplers, hoses and cables
are disconnected.
5PA41540
ENGINE REMOVAL

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ENG
EC4M5000
ASSEMBLY AND INSTALLATION
Engine installation
1. Install:

Engine 1
Install the engine from right side.

Pivot shaft 2

Engine mounting bolt (front) 3

Engine mounting bolt (lower) 4
NOTE:
Apply the molybdenum disulfide grease on the
pivot shaft.
5PA41550
T R..63 Nm (6.3 m · kg, 45 ft · lb)
T R..69 Nm (6.9 m · kg, 50 ft · lb)
T R..69 Nm (6.9 m · kg, 50 ft · lb)
Drive sprocket
1. Install:

Drive sprocket 1

Drive chain 2
NOTE:
Install the drive sprocket together with the
drive chain.
5PA41560
2. Install:

Lock washer 1

Nut (drive sprocket) 2
NOTE:
Tighten the nut while applying the rear brake.
3. Bend the lock washer tab to lock the nut.
5PA41570
T R..60 Nm (6.0 m · kg, 43 ft · lb)
4. Install:

Gasket (left crankcase cover)

Left crankcase cover 1

Screw (left crankcase cover) 2
NOTE:
Tighten the screws in stage, using a crisscross
pattern.
5PA41580
T R..5 Nm (0.5 m · kg, 3.6 ft · lb)
ENGINE REMOVAL

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ENG
CRANKCASE AND CRANKSHAFT
5PAR0009
Extent of removal:
1 Crankcase separation
2 Crankshaft removal
3 Crankshaft bearing removal
Extent of removal Order Part name Q’ty Remarks
CRANKCASE AND CRANK-
SHAFT REMOVAL
Preparation for removal Engine Refer to “ENGINE REMOVAL” section.
Piston Refer to “CYLINDER HEAD, CYLINDER
AND PISTON” section.
Primary drive gear
Refer to “KICK SHAFT, SHIFT SHAFT
AND PRIMARY DRIVE GEAR” section. Kick idle gear
Stopper lever assembly
Rotor and stator Refer to “CDI MAGNETO” section.
1 Screw (crankcase) 11
2 Crankcase oil seal holder 1
3 Right crankcase 1
Use special tool.
Refer to “REMOVAL POINTS”.
4 Left crankcase 1
5 Crankshaft 1 Use special tool.
Refer to “REMOVAL POINTS”.
6 Oil seal 2
7 Bearing 2 Refer to “REMOVAL POINTS”.
2
1
3
CRANKCASE AND CRANKSHAFT

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ENG
REMOVAL POINTS
Crankcase
1. Remove:

Right crankcase 1
Use the crankcase separating tool 2.
NOTE:

Fully tighten the tool holding bolts, but make
sure the tool body is parallel with the case. If
necessary, one screw may be backed out
slightly to level tool body.

As pressure is applied, alternately tap on the
front engine mounting boss and transmission
shafts.
CAUTION:

Turn the segment 3 to the position
shown in the figure so that it does not
contact the crankcase.

Use soft hammer to tap on the case half.
Tap only on reinforced portions of case.
Do not tap on gasket mating surface.
Work slowly and carefully. Make sure the
case halves separate evenly. If one end
“hangs up”, take pressure off the push
screw, realign, and start over. If the cases
do not separate, check for a remaining
case screw or fitting. Do not force.
EC4N3301
Crankshaft
1. Remove:

Crankshaft 1
Use the crankcase separating tool 2.
NOTE:
Make appropriate bolts 3 as shown available
by yourself and attach the tool with them.
CAUTION:
Do not use a hammer to drive out the
crankshaft.
Crankcase separating tool:
YU-1135-A/90890-01135
Crankcase separating tool:
YU-1135-A/90890-01135
5PA41600
5PA41610
5PA41620
CRANKCASE AND CRANKSHAFT

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ENG
EC4N3401
Crankshaft bearing
1. Remove:

Bearing 1
NOTE:

Remove the bearing from the crankcase by
pressing its inner race as shown in È.

If the bearing is removed together with the
crankshaft, remove the bearing using a gen-
eral bearing puller 2 as shown in É.

Do not use the removed bearing.
5PA41630
EC4N4000
INSPECTION
Crankcase
1. Inspect:

Contacting surface a
Scratches → Replace.

Engine mounting boss b, crankcase
Cracks/damage → Replace.
5PA41650
2. Inspect:

Bearing 1
Rotate inner race with a finger.
Rough spot/seizure → Replace.
5PA41660
3. Inspect:

Oil seal 1
Damage → Replace.
5PA41670
È
É
CRANKCASE AND CRANKSHAFT

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ENG
4. Install:

Dowel pin 1

Right crankcase 2
To left crankcase 3.
NOTE:

Turn the shift cam 4 to the position shown in
the figure so that it does not contact the
crankcase when installing the crankcase.

Fit the right crankcase onto the left crank-
case. Tap lightly on the case with soft ham-
mer.

When installing the crankcase, the connect-
ing rod should be positioned at TDC (top
dead center).
5PA41760
5PA41770
5. Install:

Clamp 1

Screw (crankcase) 2
NOTE:
Tighten the crankcase tightening screws in
stage, using a crisscross pattern.
5PA41780
T R..8 Nm (0.8 m · kg, 5.8 ft · lb)
6. Install:

Crankcase oil seal holder 1

Bolt (crankcase oil seal holder) 2
7. Remove:

Sealant
Forced out on the cylinder mating surface.
8. Apply:

Engine oil
To the crank pin, bearing, oil delivery hole
and connecting rod end washer.
9. Check:

Crankshaft and transmission operation
Unsmooth operation → Repair.
5PAR0010
T R..20 Nm (2.0 m · kg, 14 ft · lb)
CRANKCASE AND CRANKSHAFT