Yamaha YFM400FAR, Service Manual

Page: 154 / 481

4 - 31
ENG
CYLINDER AND PISTON
3.Measure:
●
Ring end gap
Out of specification
→
Replace.
NOTE:
You cannot measure the end gap on the
expander spacer of the oil control ring. If the oil
control ring rails show excessive gap, replace
all three rings.
End gap
Standard Limit
Top
ring
0.20 ~ 0.40 mm
(0.0079 ~ 0.0157 in)
0.65 mm
(0.0256 in)
2nd
ring
0.40 ~ 0.60 mm
(0.0157 ~ 0.0236 in)
0.95 mm
(0.0374 in)
Oil
ring
0.2 ~ 0.7 mm
(0.0079 ~ 0.0276 in)
—
CHECKING THE PISTON PIN
1.Check:
●
Piston pin
Blue discoloration/grooves
→
Replace, then
check the lubrication system.
2.Measure:
●
Piston pin-to-piston clearance
*****************************************************
Measurement steps:
●
Measure the piston pin outside diameter
a
.
If out of specification, replace the piston pin.
●
Measure the piston inside diameter
b
.
●
Calculate the piston pin-to-piston clearance
with the following formula.
Outside diameter (piston pin):
19.991 ~ 20.000 mm
(0.7870 ~ 0.7874 in)
<Limit>: 19.971 mm (0.7863 in)
Piston pin bore inside diameter:
20.004 ~ 20.015 mm
(0.7876 ~ 0.7880 in)
<Limit>: 20.045 mm (0.7892 in)
Piston pin-to-piston clearance =
Bore size (piston pin)
b
–
Outside diameter (piston pin)
a