check engine YAMAHA YZ85 2004 User Guide

3 - 10
INSP
ADJTHROTTLE CABLE ADJUSTMENT/
THROTTLE LUBRICATION
EC35A001
THROTTLE CABLE ADJUSTMENT
1. Check:

Throttle grip free play a
Out of specification → Adjust.
Throttle grip free play
a:
3 ~ 5 mm (0.12 ~ 0.20 in)
5PA30110
2. Adjust:

Throttle grip free play
Throttle grip free play adjustment steps:

Loosen the locknut 1.

Turn the adjuster 2 until the specified free
play is obtained.

Tighten the locknut.
NOTE:
Before adjusting the throttle cable free play,
the engine idle speed should be adjusted.
WARNING
After adjusting, turn the handlebar to
right and left and make sure that the
engine idling does not run faster.
5PA30120
THROTTLE LUBRICATION
1. Remove:

Throttle cable cap 1
5PA30130
2. Apply:

Lithium soap base grease
On the throttle cable end a and tube guide
cable winding portion b.
3. Install:

Throttle grip cap
5PA30140
T R..1 Nm (0.1 m · kg, 0.7 ft · lb)

3 - 23
INSP
ADJ
DRIVE CHAIN SLACK ADJUSTMENT
5. Install:

Drive chain 1

Joint 2

Master link clip 3
CAUTION:
Be sure to install the master link clip to the
direction as shown.
aTurning direction5PA30530
6. Lubricate:

Drive chain
Drive chain lubricant:
SAE 10W-30 motor oil or suit-
able chain lubricants
5PA30540
EC36A060
DRIVE CHAIN SLACK ADJUSTMENT
1. Elevate the rear wheel by placing the suit-
able stand under the engine.
2. Check:

Drive chain slack
a
In the center between the drive axle and
rear wheel axle.
Out of specification → Adjust.
NOTE:
Before checking and/or adjusting, rotate the
rear wheel through several revolutions and
check the slack several times to find the tight-
est point. Check and/or adjust chain slack with
rear wheel in this “tight chain” position.
Drive chain slack:
35 ~ 45 mm (1.4 ~ 1.8 in)
5PA30550

3 - 32
INSP
ADJ
EC36T000
WHEEL INSPECTION
1. Inspect:

Wheel runout
Elevate the wheel and turn it.
Abnormal runout → Replace.
5PA30700
2. Inspect:

Bearing free play
Exist play → Replace.
5PA30710
STEERING HEAD INSPECTION AND
ADJUSTMENT
1. Elevate the front wheel by placing a suit-
able stand under the engine.
2. Check:

Steering stem
Grasp the bottom of the forks and gently
rock the fork assembly back and forth.
Free play → Adjust steering head.
3. Check:

Steering smooth action
Turn the handlebar lock to lock.
Unsmooth action → Adjust steering ring
nut.
5PA30720
5PA30730
WHEEL INSPECTION/
STEERING HEAD INSPECTION AND ADJUSTMENT

3 - 36
INSP
ADJ
ELECTRICAL/SPARK PLUG INSPECTION
EC370000
ELECTRICAL
EC371001
SPARK PLUG INSPECTION
1. Remove:

Spark plug
2. Inspect:

Electrode 1
Wear/damage → Replace.

Insulator color 2
Normal condition is a medium to light tan
color.
Distinctly different color → Check the
engine condition.
NOTE:
When the engine runs for many hours at low
speeds, the spark plug insulator will become
sooty, even if the engine and carburetor are in
good operating condition.
3. Measure:

Plug gap a
Use a wire gauge or thickness gauge.
Out of specification → Regap.
4. Clean the plug with a spark plug cleaner if
necessary.
Spark plug gap:
0.5 ~ 0.6 mm (0.020 ~ 0.024 in)
5PA30850
5. Tighten:

Spark plug
NOTE:

Before installing a spark plug, clean the gas-
ket surface and plug surface.

Finger-tighten a the spark plug before torqu-
ing to specification b.
5PA30860
T R..20 Nm (2.0 m · kg, 1.4 ft · lb)

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 - 54
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

4 - 58
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

6 - 2
–+ELECIGNITION SYSTEM
EC620000
IGNITION SYSTEM
INSPECTION STEPS
Use the following steps for checking the possibility of the malfunctioning engine being attributable to
ignition system failure and for checking the spark plug which will not spark.
*marked: Only when the ignition checker is used.
NOTE:

Remove the following parts before inspection.
1) Seat
2) Fuel tank

Use the following special tools in this inspection.
Dynamic spark tester:
YM-34487
Ignition checker:
90890-06754Pocket tester:
YU-3112-C/90890-03112
Spark gap test*Clean or replace
spark plug.
Check entire ignition
system for connection.Repair or replace.
Check engine stop switch. Replace.
Check ignition coil. Primary coil Replace.
Secondary coil Replace.
Check spark plug cap. Replace.
Check CDI magneto. Pickup coil Replace.
Charging coil Replace.
Replace CDI unit.
No spark
OK
OK
OK
OK
OK
Spark
No good
No good
No good
No good
No good
No good
No good