Yamaha F90D, Service Manual

Page: 107 / 241

POWR
Power unit
5-41
6D81G11
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
50 mm (2.0 in)
c
80 mm (3.1 in)
2. Calculate the taper limit. Replace or
rebore the cylinder block if above specifi-
cation.
3. Calculate the out-of-round limit. Replace
or rebore the cylinder block if above
specification.
Checking the piston clearance
1. Calculate the piston clearance using the
piston outside diameter and the cylinder
bore. Replace the piston and piston rings
as a set or the cylinder block or all parts,
or rebore the cylinder if out of specifica-
tion.
Checking the piston rings
1. Check the piston ring dimensions of B
and T. Replace if out of specification.
2. Level the piston ring
1
in the cylinder
with a piston crown.
3. Check the piston ring end gap
d
at the
specified measuring point. Replace if out
of specification.
Cylinder bore (D
1
–D
6
):
79.000–79.020 mm
(3.1102–3.1110 in)
Taper limit:
D
1
–D
5
(direction
d
)
D
2
–D
6
(direction
e
)
0.08 mm (0.0031 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)
S60C5830
D
1
D
2
D
3
D
4
D
5
D
6
c b
a
d
e
Piston clearance:
0.070–0.080 mm
(0.0028–0.0031 in)
Piston ring dimensions:
Top ring
a
:
B: 1.17–1.19 mm
(0.0461–0.0469 in)
T: 2.80–3.00 mm
(0.1102–0.1181 in)
Second ring
b
:
B: 1.47–1.49 mm
(0.0579–0.0587 in)
T: 3.00–3.20 mm
(0.1181–0.1260 in)
Oil ring
c
:
B: 2.38–2.48 mm
(0.0937–0.0976 in)
T (reference data):
2.40 mm (0.0945 in)