Yamaha YFM660 01 User Manual

5 - 21
ENGCAMSHAFT AND CYLINDER HEAD
3.Measure:

Cylinder head warpage
Out of specification →
 Resurface.
***********************************************
Warpage measurement and resurfacing
steps:

Place a straightedge and a feeler gauge
across the cylinder head.

Use a feeler gauge to measure the warpage.

If the warpage is out of specification, resur-
face the cylinder head.

Place a 400 ~ 600 grit wet sandpaper on the
surface plate, and resurface the head using
a figure-eight sanding pattern.
NOTE:
To...

5 - 22
ENGCAMSHAFT AND CYLINDER HEAD
2.Install:

Camshaft

Camshaft sprocket
***********************************************
Installation steps:

Turn the crankshaft counterclockwise with a
wrench.

Align the “I” mark 1
 on the rotor with the sta-
tionary pointer 2
 on the crankcase cover.
When the “I” mark is aligned with the station-
ary pointer, the piston is at the Top Dead
Center (T.D.C.).
CAUTION:
Do not turn the crankshaft during the cam-
shaft installation.

Temporarily install the camshaft...

5 - 23
ENGCAMSHAFT AND CYLINDER HEAD

Install the decompressor cam guide plates 9
and camshaft sprocket bolts 0
.

Remove the retaining wire.
***********************************************
T R..
Camshaft sprocket bolt:
20 Nm (2.0 m  kg, 14 ft  lb)
3.Install:

Timing chain tensioner
***********************************************
Installation steps:

Remove the timing chain tensioner cap bolt
1
, washer 2
 and spring 3
.

Release the timing chain tensioner one-way
cam 4
 and push the tensioner rod 5...

5 - 24
ENGVALVES AND VALVE SPRINGS
VALVES AND VALVE SPRINGS
Order Job name/Part name Q’ty Remarks
Removing the valve and valve 
springRemove the parts in the order below.
Cylinder head Refer to “CAMSHAFT AND CYLINDER
HEAD”.
1 Valve cotter 10
Refer to “REMOVING/INSTALLING THE 
VALVE AND VALVE SPRING”. 2 Valve spring retainer 5
3 Intake valve spring 3
4 Exhaust valve spring 2
5 Intake valve 3
6 Exhaust valve 2
7 Valve stem seal 5
8 Valve spring seat 5
For installation, reverse the removal pro-
cedure. 

5 - 25
ENGVALVES AND VALVE SPRINGS
REMOVING THE VALVE AND VALVE 
SPRING
1.Check:

Valve sealing
Leakage at the valve seat →
 Inspect the
valve face, valve seat and valve seat width.
Refer to “VALVE AND VALVE SPRING
INSPECTION”.
***********************************************
Checking steps:

Pour a clean solvent 1
 into the intake and
exhaust ports.

Check that the valve seals properly.
There should be no leakage at the valve seat
2
.
***********************************************
2.Remove:

Valve...

5 - 26
ENGVALVES AND VALVE SPRINGS
CHECKING THE VALVE AND VALVE 
SPRING
1.Measure:

Stem-to-guide clearance
Out of specification →
 Replace the valve
guide.Stem-to-guide clearance =
valve guide inside diameter a –
valve stem diameter b 
Clearance (stem to guide):
Intake:
0.010 ~ 0.037 mm
(0.0004 ~ 0.0015 in)
: 0.08 mm (0.0031 in)
Exhaust:
0.025 ~ 0.052 mm
(0.0010 ~ 0.0020 in)
: 0.10 mm (0.0039 in)
2.Replace:

Valve guide
***********************************************
Replacement steps:
NOTE:
To ease...

5 - 27
ENGVALVES AND VALVE SPRINGS
3.Check:

Valve face
Pitting/wear →
 Grind the face.

Valve stem end
Mushroom shape or diameter larger than the
body of the stem →
 Replace.
4.Measure:

Margin thickness a
 
Out of specification →
 Replace.
Margin thickness:
Intake:
0.85 ~ 1.15 mm 
(0.0335 ~ 0.0453 in)
Exhaust:
0.85 ~ 1.15 mm 
(0.0335 ~ 0.0453 in)
5.Measure:

Runout (valve stem)
Out of specification →
 Replace.
NOTE:

When installing a new valve always replace
the guide.

If the valve is removed or...

5 - 28
ENGVALVES AND VALVE SPRINGS
8.Measure:

Valve seat width a
 
Out of specification →
 Reface the valve seat.
***********************************************
Measurement steps:

Apply Mechanic’s blueing dye (Dykem) b
 to
the valve face.

Install the valve into the cylinder head.

Press the valve through the valve guide and
onto the valve seat to make a clear pattern.

Measure the valve seat width. Where the
valve seat and valve face made contact,
blueing will have been removed.

If the valve seat is...

5 - 29
ENGVALVES AND VALVE SPRINGS

Install the valve into the cylinder head.

Turn the valve until the valve face and valve
seat are evenly polished, then clean off all of
the compound.
NOTE:
For best lapping results, lightly tap the valve
seat while rotating the valve back and forth
between your hands.

Apply a fine lapping compound to the valve
face and repeat the above steps.
NOTE:
After every lapping operation be sure to clean
off all of the compound from the valve face and
valve seat.

Apply...

5 - 30
ENGVALVES AND VALVE SPRINGS
11.Measure:

Compressed spring force a
 
Out of specification →
 Replace.
b
Installed length
Compressed spring force:
Inner:
149 ~ 173 N at 27.2 mm
(15.19 ~ 17.64 kg, 
33.50 ~ 38.89 lb at 1.07 in)
Outer:
165 ~ 191 N at 30.7 mm
(16.83 ~ 19.49 kg, 
37.09 ~ 42.94 lb at 1.21 in)
12.Measure:

Spring tilt a
 
Out of specification →
 Replace.
Spring tilt limit:
Inner:
2.5°/1.6 mm (0.06 in)
Outer:
2.5°/1.6 mm (0.06 in)
INSTALLING THE VALVE AND VALVE 
SPRING
1.Apply:

Molybdenum...