Yamaha F4B - Checking the Cylinder Bore; Checking the Piston Ring; Checking the Piston Ring End Gap

7-41
POWR
Power unit
Checking the cylinder bore
1. Measure the cylinder bore (D1–D6) at
measuring points a, b, and c, and in
direction d (D1, D3, D5), which is paral-
lel to the crankshaft, and in direction e
(D2, D4, D6), which is at a right angle to
the crankshaft.
a 5.0 mm (0.20 in)
b 28.0 mm (1.10 in)
c 50.0 mm (1.97 in)
Checking the piston ring
1. Measure the piston ring dimensions B
and T.
Checking the piston ring end gap
1. Level the piston ring a in the cylinder
with a piston crown at the specified mea-
suring point a.
2. Measure the piston ring end gap b.
Piston diameter a:
61.950–61.965 mm
(2.4390–2.4396 in)
Measuring point b:
1.0 mm (0.04 in) up from the bottom
of the piston skirt
Oversize piston diameter:
Oversize 1st:
62.200–62.215 mm
(2.4488–2.4494 in)
Oversize 2nd:
62.450–62.465 mm
(2.4587–2.4592 in)
Cylinder bore (D1–D6):
62.000–62.015 mm
(2.4409–2.4415 in)
D
1
D
2
D
3
D
4
D
5
D
6
a
b
c
d
e
Piston ring dimensions:
Top ring a:
B: 1.170–1.190 mm (0.0461–0.0469 in)
T: 2.500–2.700 mm (0.0984–0.1063 in)
2nd ring b:
B: 1.170–1.190 mm (0.0461–0.0469 in)
T: 2.600–2.800 mm (0.1024–0.1102 in)
Oil ring c:
B: 1.850–2.000 mm (0.0728–0.0787 in)
T: 2.550–2.850 mm (0.1004–0.1122 in)
(reference data)
Measuring point a (reference data):
60.0 mm (2.36 in)
Piston ring end gap b (reference data):
Top ring:
0.110–0.210 mm (0.0043–0.0083 in)
2nd ring:
0.260–0.410 mm (0.0102–0.0161 in)
Oil ring:
0.200–0.700 mm (0.0079–0.0276 in)
a
b
c
T
B
T
T
B
B
a
b
a