Checking The Cylinder Bore; Checking The Piston Clearance; Checking The Piston Rings - Yamaha F2.5A Service Manual

POWR

Checking the cylinder bore

1. Measure the cylinder bore (D
) at measuring points a, b,
D , D , D
4 5 6
and c, and in direction d (D
which is parallel to the crankshaft, and
direction e (D
2
right angle to the crankshaft.
a
b
D
2
c
D
4
D
6
Cylinder bore (D
54.000–54.015 mm
(2.1260–2.1266 in)
2. Calculate the taper limit. Replace or
rebore the cylinder block if out of 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 out of spec-
ification.
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 specifications. Replace the piston
and piston rings as a set or the cylinder
block or all parts, or rebore the cylinder if
out of specification.
5-25
Power unit
, D , D
1 2
, D , D
1 3
, D , D ), which is at a
4 6
D
1
D
3
D
5
S69J5B70
, D , D , D , D , D
1 2 3 4 5
Piston clearance:
,
3
),
5

Checking the piston rings

1. Check the piston ring dimensions of B
and T. Replace if out of specification.
d
e
):
6
Piston ring dimensions:
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.
0.035–0.065 mm
(0.0014–0.0026 in)
Top ring a:
B: 0.97–0.99 mm
(0.0382–0.0390 in)
T: 1.95–2.15 mm
(0.0768–0.0846 in)
Second ring b:
B: 1.17–1.19 mm
(0.0461–0.0468 in)
T: 2.30–2.50 mm
(0.0906–0.0984 in)
Oil ring c:
B: 1.87–1.95 mm
(0.0736–0.0768 in)
T: 2.10–2.40 mm
(0.0827–0.0945 in)
69M3E11