Yamaha YZF-R25 Service Manual page 106

Valve lapper
90890-04101
Valve lapping tool
YM-A8998
TIP
• Cover the timing chain opening with a rag to
prevent the valve pad from falling into the
crankcase.
• Make a note of the position of each valve lifter
"1" and valve pad "2" so that they can be in-
stalled in the correct place.
b. Calculate the difference between the speci-
fied valve clearance and the measured valve
clearance.
Example:
Specified valve clearance = 0.11–0.18 mm
(0.0043–0.0071 in)
Measured valve clearance = 0.25 mm
(0.0098 in)
0.25 mm (0.0098 in)–0.18 mm (0.0071 in) =
0.07 mm (0.0028 in)
c. Check the thickness of the current valve pad.
TIP
The thickness "a" of each valve pad is marked in
hundredths of millimeters on the side that touch-
es the valve lifter.
Example:
If the valve pad is marked "158", the pad
thickness is 1.58 mm (0.0622 in).
PERIODIC MAINTENANCE
158
d. Calculate the sum of the values obtained in
steps (b) and (c) to determine the required
valve pad thickness and the valve pad num-
ber.
Example:
1.58 mm (0.0622 in) + 0.07 mm (0.0028 in) =
1.65 mm (0.0649 in)
The valve pad number is 165.
e. Round off the valve pad number according to
the following table, and then select the suit-
able valve pad.
Last digit
0, 1, 2
3, 4, 5, 6
7, 8, 9
TIP
Refer to the following table for the available
valve pads.
Valve pad range
Valve pad thickness
Available valve pads
Example:
Valve pad number = 165
Rounded value = 165
New valve pad number = 165
f. Install the new valve pad "1" and the valve lift-
er "2".
TIP
• Lubricate the valve lifter with engine oil.
• Install the valve lifter and the valve pad in the
correct place.
• The valve lifter must turn smoothly when rotat-
ed by hand.
3-7
a
Rounded value
0
5
10
No. 150–240
1.50–2.40 mm
(0.0590–0.0944 in)
63 thicknesses in 0.012
mm (0.00047 in) incre-
ments