Yamaha YFM660 01 User Manual

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ENGCYLINDER HEAD COVER
CHECKING THE TAPPET COVER
1.Check:

Tappet cover (intake) 1
 

Tappet cover (exhaust) 2
 

O-ring 3
 New
INSTALLING THE CYLINDER HEAD COVER
1.Apply:

Sealant (Quick Gasket) 1
 
(to the mating surfaces of the cylinder head
and cylinder head cover)
2.Install:

Cylinder head cover

Cable guides 1
 

Washers 2
 

Bolts
3Bolt:   = 25 mm
4Bolt:   = 40 mm
5Bolt:   = 55 mm
6Bolt:   = 115 mm
7Bolt:   = 130 mm
NOTE:
Tighten the cylinder head cover bolts in
stages, using a crisscross...

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ENGROCKER ARMS
ROCKER ARMS
Order Job name/Part name Q’ty Remarks
Removing the rocker arm
Remove the parts in the order below.
Cylinder head cover Refer to “CYLINDER HEAD COVER”.
1 Plug/O-ring 1/1
2Bolt 2
3 Rocker arm shaft 2/O-ring 1/1
Refer to “REMOVING/INSTALLING THE 
ROCKER ARM”. 4 Rocker arm 3 1
5 Rocker arm shaft 3/O-ring 1/1
6 Rocker arm 4 1
7 Rocker arm shaft 1/O-ring 1/1
8 Rocker arm 1 1
9 Rocker arm 2 1 

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ENGROCKER ARMS
Order Job name/Part name Q’ty Remarks
10 Spring 4
11 Locknut 5
12 Valve adjuster 5
For installation, reverse the removal pro-
cedure. 

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ENGROCKER ARMS
REMOVING THE ROCKER ARM
1.Remove:

Rocker arm shafts 1
 

Rocker arms 2
 
NOTE:
Use a slide hammer bolt 3
 and weight 4
 to
remove the rocker arm shafts.
Slide hammer set:
P/N. YU-01083-A
Slide hammer bolt (M6):
P/N. 90890-01083
Weight:
P/N. 90890-01084
CHECKING THE ROCKER ARM
1.Check:

Rocker arm lobes 1
 

Valve adjusters 2
 
Blue discoloration/pitting/scratches →
 
Replace.
2.Check:

Rocker arms

Rocker arm shafts
Damage/wear →
 Replace....

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ENGROCKER ARMS

Measure the outside diameter b
 of the
rocker arm shafts.
Out of specification →
 Replace.

Calculate the clearance by subtracting the
rocker arm shaft outside diameter from the
rocker arm inside diameter.
Clearance greater than 0.08 mm (0.003 in)
→
 Replace the defective part(s).
***********************************************
Rocker arm outside diameter:
11.976 ~ 11.991 mm
(0.4715 ~ 0.4721 in)
Rocker arm to shaft standard 
clearance:
0.009 ~ 0.042 mm
(0.0004 ~ 0.0017 in)...

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ENGCAMSHAFT AND CYLINDER HEAD
CAMSHAFT AND CYLINDER HEAD
Order Job name/Part name Q’ty Remarks
Removing the camshaft and cylin-
der headRemove the parts in the order below.
Seat/front fender
Refer to “SEAT, FENDERS AND FUEL 
TANK” in CHAPTER 3.
Fuel tank/rubber covers
Carburetors Refer to “CARBURETORS” in CHAPTER 
7.
Water jacket outlet pipe Refer to “THERMOSTAT” in CHAPTER 6.
Muffler/exhaust pipe Refer to “ENGINE REMOVAL”.
Cylinder head cover Refer to “CYLINDER HEAD COVER”.
1 Timing chain...

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ENGCAMSHAFT AND CYLINDER HEAD
Order Job name/Part name Q’ty Remarks
6 Camshaft 1
Refer to “CAMSHAFT AND CYLINDER 
HEAD”.
7 Cylinder head 1
8 Cylinder head gasket 1
9 Dowel pin 2
10 Carburetor joint 1 1
11 Carburetor joint 2 1
For installation, reverse the removal pro-
cedure. 

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ENGCAMSHAFT AND CYLINDER HEAD
REMOVING THE CAMSHAFT AND CYLIN-
DER HEAD
1.Loosen:

Camshaft sprocket bolts 1
 
2.Loosen:

Timing chain tensioner cap bolt
3.Remove:

Timing chain tensioner

Timing chain guide (exhaust)

Decompressor cam guide plates

Camshaft sprocket
NOTE:

Fasten a safety wire to the timing chain to
prevent it from falling into the crankcase.

When removing the camshaft sprocket, it is
not necessary to separate the timing chain.
4.Remove:

Cylinder head
NOTE:

Loosen the bolts in...

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ENGCAMSHAFT AND CYLINDER HEAD
CHECKING THE CAMSHAFT
1.Check:

Cam lobes
Pitting/scratches/blue discoloration →
 
Replace.
2.Measure:

Cam lobes length a
 and b
.
Out of specification →
 Replace.
Camshaft lobe limit:
Intake:
a 35.59 mm (1.4012 in)
b 30.05 mm (1.1831 in)
Exhaust:
a 36.40 mm (1.4331 in)
b 30.05 mm (1.1831 in)
CHECKING THE CAMSHAFT SPROCKET
1.Check:

Camshaft sprocket
Wear/damage →
 Replace the camshaft 
sprocket and timing chain as a set.
a
1/4 of a tooth
b
Correct
1Timing chain...

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ENGCAMSHAFT AND CYLINDER HEAD
CHECKING THE TIMING CHAIN GUIDE
1.Check:

Exhaust side timing chain guide 
Wear/damage →
 Replace.
CHECKING THE TIMING CHAIN TEN-
SIONER
1.Check:

One-way cam operation (tensioner) 
Unsmooth operation →
 Replace.
CHECKING THE CYLINDER HEAD
1.Eliminate:

Carbon deposits (from the combustion 
chambers)
Use a rounded scraper.
NOTE:
Do not use a sharp instrument to avoid damag-
ing or scratching:

Spark plug threads

Valve seats
2.Check:

Cylinder head
Scratches/damage →...