Checking The Cylinder Bore; Checking The Piston Clearance; Checking The Piston Rings - Yamaha F80B Service Manual

Checking the cylinder bore

1. Measure the cylinder bore (D
measuring points a, b, and c, and in
direction d (D
, D
1 3
to the crankshaft, and direction e (D
D , D ), which is at a right angle to the
4 6
crankshaft.
a
c b
D
2
D
4
D
6
a 20 mm (0.8 in)
b 50 mm (2.0 in)
c 80 mm (3.1 in)
Cylinder bore (D
79.000–79.020 mm
(3.1102–3.1110 in)
2. Calculate the taper limit. Replace or
rebore the cylinder block if above specifi-
cation.
Taper limit:
(direction d)
D –D
1 5
(direction e)
D –D
2 6
0.08 mm (0.0031 in)
3. Calculate the out-of-round limit. Replace
or rebore the cylinder block if above
specification.
Out-of-round limit:
(measuring point a)
D –D
2 1
(measuring point c)
D –D
6 5
0.05 mm (0.0020 in)

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.
6D93G11
–D ) at
1 6
, D ), which is parallel
5
,
2
D
1
d
D
3 e
D
5
S60C5830
–D ):
1 6
Piston clearance:
0.070–0.080 mm
(0.0028–0.0031 in)

Checking the piston rings

1. Check the piston ring dimensions of B
and T. Replace if out of specification.
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)
2. Level the piston ring 1 in the cylinder
with a piston crown.
Cylinder block
1
2
3
4
5
6
7
8
9
5-42