Yamaha F50F, Service Manual

Page: 130 / 305

POWR
Power unit
5-39
6C13G11
Checking the piston diameter
1. Measure the piston outside diameter at
the specified measuring point. Replace if
out of specification.
Checking the cylinder bore
1. Measure the cylinder bore (D
1
–D
6
) at
measuring points
a
,
b
, and
c
, and in
direction
d
(D
1
, D
3
, D
5
), which is parallel
to the crankshaft, and direction
e
(D
2
,
D
4
, D
6
), which is at a right angle to the
crankshaft.
a
20 mm (0.8 in)
b
40 mm (1.6 in)
c
70 mm (2.8 in)
2. Calculate the taper limit. Replace the cyl-
inder block if above specification.
3. Calculate the out-of-round limit. Replace
the cylinder block if above specification.
Checking the piston clearance
1. Replace the piston and piston rings as a
set or the cylinder block, or all parts if out
of specification.
Checking the piston rings
1. Check the piston ring dimensions of B
and T. Replace if out of specification.
Piston diameter
a
:
64.950–64.965 mm
(2.5571–2.5577 in)
Measuring point
b
:
5.0 mm (0.20 in) up from the
bottom of the piston skirt
Oversize piston diameter:
Oversize 1st:
65.200–65.215 mm
(2.5669–2.5675 in)
Oversize 2nd:
65.450–65.465 mm
(2.5768–2.5774 in)
S69J5B70
D
1
D
2
D
3
D
4
D
5
D
6
a
b
c
d
e
Cylinder bore (D
1
–D
6
):
65.000–65.015 mm
(2.5591–2.5596 in)
Taper limit:
D
1
–D
5
(direction
d
)
D
2
–D
6
(direction
e
)
0.08 mm (0.0032 in)
Out-of-round limit:
D
2
–D
1
(measuring point
a
)
D
6
–D
5
(measuring point
c
)
0.05 mm (0.0020 in)
Piston clearance:
0.035–0.065 mm
(0.0014–0.0026 in)