Checking The Piston Pin - Yamaha YFM45FAR Service Manual

CYLINDER AND PISTON
3.Measure:
Ring end gap
G
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.
Top
ring
2nd
ring
Oil
ring

CHECKING THE PISTON PIN

1.Check:
Piston pin
G
Blue discoloration/grooves → Replace, then
check the lubrication system.
2.Measure:
Piston pin-to-piston clearance
G
*****************************************************
Measurement steps:
Measure the piston pin outside diameter a.
G
If out of specification, replace the piston pin.
Outside diameter (piston pin):
19.991 ~ 20.000 mm
(0.7870 ~ 0.7874 in)
<Limit>: 19.971 mm (0.7863 in)
Measure the piston inside diameter b.
G
Piston pin bore inside diameter:
20.004 ~ 20.015 mm
(0.7876 ~ 0.7880 in)
<Limit>: 20.045 mm (0.7892 in)
G
Calculate the piston pin-to-piston clearance
with the following formula.
Piston pin-to-piston clearance =
Bore size (piston pin) b –
Outside diameter (piston pin) a
4 - 31
ENG
End gap
Standard
0.20 ~ 0.40 mm
(0.0079 ~ 0.0157 in)
0.40 ~ 0.60 mm
(0.0157 ~ 0.0236 in)
0.2 ~ 0.7 mm
(0.0079 ~ 0.0276 in)
Limit
0.65 mm
(0.0256 in)
0.95 mm
(0.0374 in)
—