Yamaha EK40G, Service Manual

Page: 86 / 200

POWR
5-29 6H95G11
Power unit
Checking the piston diameter
1. Measure the piston outside diameter at
the specified measuring point. Replace if
out of specification.
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.
Checking the piston rings
1. Check the piston ring dimensions of B
and T. Replace if out of specification.
2. Level the piston rings 1 in a cylinder with
a piston crown.
3. Check the piston ring end gap
c
at the
specified measuring point. Replace if out
of specification.
T
B
T
6B450460
B
a
b
Piston outside diameter:
77.940—77.965 mm
(3.0685—3.0695 in)
Measuring point
a
:
10.0 mm (0.39 in) up from the
bottom of the piston skirt.
Oversize piston diameter:
1st:
78.190—78.215 mm
(3.0783—3.0793 in)
2nd:
78.440—78.465 mm
(3.0882—3.0892 in)
Piston clearance:
0.055–0.060 mm
(0.0022–0.0024 in)
Piston ring dimensions
Top ring
a
and 2nd piston ring
b
:
B: 1.970—1.990 mm
(0.0776—0.0783 in)
T: 2.500—2.700 mm
(0.0984—0.1063 in)
6F650430
d
c
1
1
Piston ring end gap
c
:
Top ring and 2nd piston ring:
0.30—0.50 mm
(0.0118—0.0197 in)
Measuring point
d
:
10.0 mm (0.39 in)
6H95G11_05 04.8.20 11:05 Page 30