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ENGINE MAINtiENANCE
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Piston and Piston Ring Maintenance
Remedies:
(1) If any piston ring
is
found
stuck, poor sealing wil
I
result.
(2) If the cylinder
wall is scuffed, poor sealing will
result as in the case
of the piston
ring
being stuck.
In the above two cases,
the piston ring should be
replaced with a new
one, and at the same
time,
the
cylinder wall should be
checked
for scratches.
(3) Whether the
contact
between the
piston ring and
the
cylinder
wall is
good or not will have a great
effect
on sealing.
The
entire area of the piston
ring face must be
in
tight
contact with the cylinder
wall. If excess wear
is found on
the
upper or
the
lower half of the piston ring face, the piston ring
groove is considered to be
worn
uneve
nly,
causing
the ring to
twist.
(See
Fig.
7-60)
If
imitation
piston
rings (other than genuine
Yamaha
parts)
are used,
such defects as mentioned
in
(3)
and
(4)
above may
easi
ly
occur,
and in
the
worst
case,
serious
engine
troubles may result.
(4)
When
a
good seal between the
piston
ring
bottom
and the ring groove bottom is
noticed
,
the piston
ring
is considered
to
smoothly slide in and out on
the
ring
groove
bottom in a correct manner.
7-5-4
Before replacing the piston ring, remove
carbon accumula-
tions from the gap
between the
ring
and
the
groove. The
piston ring must be
installed so
that
the locating pin
knocked in the groove
is
between
both ends of the
ring
as
illustrated.
Th is is
the
most
vital
requirement
to be
observed when the piston is
inserted into
the
cylinder.
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Fig. 7-59
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7-5-5
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The up and down
movement of
the piston
ring
in the
piston
groove
can
be
calculated
from
the
side clearan
ce
as
illustrated.
Th
is side clearance
is
created
by wear
on
the
ring bottom. If the
side
clearance
is
measured
more than
0.2
mm, the ring
should
be replaced.
The illustration
sl-iows
the
sectional view
of
a new piston
ring
installed
in the
ring
groove.
Pi
sto
n
Pi ston ring
I
(Side
clearan ce)
0 .0024
..
~_J·~=~~=====-=-=---
(0.06 mml
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Measure
w1
th
feel er
gauge
Fig.
7-60
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