Yamaha F40B - Checking the Piston Diameter; Checking the Cylinder Bore; Checking the Piston Clearance; Checking the Piston Ring

POWR
Power unit
5-43 67C3K11
Checking the piston diameter
1. Measure the piston diameter a at the
specified measuring point b. 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 in 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 60 mm (2.4 in)
Checking the piston clearance
1. Check the piston clearances if replacing
the pistons, piston ring sets, cylinder
block, or all parts.
NOTE:
The figures are for reference only. Depend-
ing on how the parts are assembled, the
actual measurements may not be within the
specified ranges.
Checking the piston ring
1. Measure the piston ring dimensions B
and T. Replace the piston ring set if out
of specification.
Piston diameter a:
64.950–64.965 mm
(2.5571–2.5577 in)
Measuring point b:
2.0 mm (0.08 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
):
64.985–65.015 mm
(2.5585–2.5596 in)
Piston clearance (reference data):
0.035–0.065 mm
(0.0014–0.0026 in)