Yamaha F25A - Piston Pin Inspection; Piston Ring Inspection; Piston-To-Cylinder Clearance

5-37
POWR
E
CRANKCASE, CRANKSHAFT ASSY., AND
CYLINDER BODY
Piston-to-cylinder clearance
1. Calculate:
● Piston-to-cylinder clearance
Out of specification → Replace the
piston and piston rings, the cylinder
or both.
Piston-to-
cylinder
clearance
=
Cylinder
bore
–
Piston
diameter
Piston-to-cylinder clearance:
0.035 ~ 0.065 mm
(0.0014 ~ 0.0026 in)
Piston pin inspection
1. Measure:
● Piston pin diameter
Out of specification → Replace the
piston pin.
Piston pin diameter:
15.965 ~ 15.970 mm
(0.6285 ~ 0.6287 in)
Piston ring inspection
1. Measure:
● End gap a
Out of specification → Replace the
piston ring.
NOTE:
Push the piston ring into the cylinder with
the piston crown.
End gap (installed):
Top piston ring:
0.15 ~ 0.30 mm
(0.006 ~ 0.012 in)
2nd piston ring:
0.30 ~ 0.50 mm
(0.012 ~ 0.020 in)
Oil ring:
0.20 ~ 0.70 mm
(0.008 ~ 0.028 in)