Yamaha 25BMH, Service Manual

Page: 250 / 446

CRANKSHAFT AND CYLINDER BODY
5-33
E
POWR
3. Measure:
• Piston diameter
(use an outside micrometer)
Out of specification
→
Replace.
NOTE:
When measuring the piston diameter, posi-
tion the micrometer in relation to the piston
pin hole as shown.
CALCULATING THE
PISTON-TO-CYLINDER CLEARANCE
Calculate:
• Piston-to-cylinder clearance.
Out of specification
→
Replace the
piston and piston rings, the cylinder
or both.
b
c
a
Outside micrometer
90890-03008
Measuring
point “H”
Piston diameter
S S S Stttta a a and nd nd nda a a arrrrd d d d
10.0 mm
(0.3937 in) 71.94 – 71.96 mm
(2.8323 – 2.8331 in)
O
O O
Ove
ve ve
ver
r r
r s
s s
siiiizzzze
e e
e p
p p
piiiis
s s
stttton d
on d on d
on diiiia
a a
am
m m
me
e e
etttte
e e
errrr::::
1 1 1 1: : : : 72 72 72 72....2 2 2 25 5 5 5 mm mm mm mm ((((2 2 2 2....84 84 84 844 4 4 45 5 5 5 iiiin n n n))))
2 2 2 2: : : : 72 72 72 72....5 5 5 50 0 0 0 mm mm mm mm ((((2 2 2 2....85 85 85 854 4 4 43 3 3 3 iiiin n n n))))
Piston-to-
cylinder
clearance
=
Cylinder
bore
diameter
–
Piston
diameter
Piston-to-cylinder clearance
0.060 – 0.065 mm
(0.0024 – 0.0026 in)