Checking The Piston Clearance; Checking The Piston Rings - Yamaha F25C Service Manual

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. Replace the piston and piston rings as a
set or the cylinder block, or all parts if out
of specification.
Piston clearance:
0.035–0.065 mm
(0.0014–0.0026 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: 2.25–2.45 mm
(0.0885–0.0965 in)
2nd ring b:
B: 1.47–1.49 mm
(0.0579–0.0587 in)
T: 2.60–2.80 mm
(0.1024–0.1102 in)
Oil ring c:
B: 2.36–2.48 mm
(0.0929–0.0976 in)
T: 2.75 mm (0.1083 in)
2. Level the piston ring 1 in the cylinder
with a piston crown.
6D55F11
3. Check the piston ring end gap d at the
specified measuring point. Replace if out
of specification.
Piston ring end gap d:
Top ring:
0.15–0.30 mm
(0.0059–0.0118 in)
2nd ring:
0.30–0.50 mm
(0.0118–0.0197 in)
Oil ring:
0.20–0.70 mm
(0.0079–0.0276 in)
Measuring point e: 20 mm (0.8 in)
Cylinder block
1
2
3
4
5
6
7
8
9
5-38