Yamaha E115A, Service Manual

Page: 118 / 261

POWR
5-37 61U5H11
Power unit
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 direction
e
(D
2
,
D
4
, D
6
), which is at a right angle to the
crankshaft.
a
: 10.0 mm (0.39 in) from the cylinder head top
surface
b
: 5.0 mm (0.20 in) above the exhaust port
upper edge
c
: 5.0 mm (0.20 in) below the scavenging port
lower edge
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.
NOTE:
Be sure to rebore the cylinder for matching
the replacement oversize pistons, when
using the specified oversize pistons.
Checking the piston ring
1. Check the piston ring dimensions of B
and T. Replace the piston and piston
rings as a set if out of specification.
2. Level the piston ring
1
in a cylinder with
a piston crown.
3. Check the piston ring end gap
a
at the
specified measuring point
b
. Replace
the piston ring set if out of specification.
T
B
69D50410
Cylinder bore (D
1
–D
6
):
90.000–90.020 mm
(3.5433–3.5441 in)
Cylinder gauge 1 :
90890-06759
Piston clearance:
0.080–0.085 mm
(0.0032–0.0033 in)
Piston ring dimension
Top ring and 2nd piston ring:
B: 1.970–1.990 mm
(0.0776–0.0783 in)
T: 2.700–2.900 mm
(0.1063–0.1142 in)
1
a
b
c
e
d
6F650370
6F650430
b
a
1
1
Piston ring end gap
a
:
E115A:
0.30–0.40 mm (0.0118–0.0157 in)
115B, 140B:
Top:
0.30–0.50 mm (0.0118–0.0197 in)
2nd:
0.30–0.40 mm (0.0118–0.0157 in)
Measuring point
b
: 10 mm (0.39 in)
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