MAINTENANCE
AND
REPAIR
,63
,cylinders
are
not being reconditioned, but new piston
rings
are
being in-
stalled,
remove
al1yridge which may have become
formed
at
the
top of
piston
ring
travel
in the
cylinder
bore.
PISTONS
AND
RINGS.-The
piston and connecting rod
assemblies
are
, , ' ,
removed
through the top of the
cylinder
• The
pistons
are
fitted with
two
compression
rings
and one oil
control
ring
with an expander . Inspect
each
piston.
The
piston
ring
grooves should
be
cleaned of any
carbondeposits,
and
the
oil
return
slots
in
the
lower
groove
must
be open.
If
the
pistons
are
badly
scored,
very
loose in the
cylinders,
have
ba.dly
worn
ring
grooves,
or
otherwise
are
not in good condition,
install
new
pistons~
Insta.ll new
pistons
if
the
old ones
are
lOOSe
on the
piston
pins
and
0.002'
inch
oversize
piston
pins
will not
correct
it. Handle
pistons
carefully
to,::\.void
nicking
the
walls,
Any
raised
surface
of
this
type
must
be
dressed
down carefully.
Conformatic type
pistons
are
designed
for
very
close
fit
in
the
cylinder
bore.
, A
slot
on opposite
sides
of the piston behind the oil
control
ring
permits
oil t·eturn and allows
lor
expansion.
The
piston
is
interchange-
able
as
to which
side
should
be
nearer
the
oil
base.
Inspect
the
rings
carefully
for
fit
in
grooves,
for
tension,
and
for
seat-
ing on
cylinder
walls.
Install
new
rings
where
there
is
any doubt about
the
condition
of
the
old
rings.
I
I
Before
installing
new
ringsonthepistcin,
check the
ring
gap
by
placing
eachring
squarely
lnits
cylinder
at
a
position
correspondlng
to
the
bot-
tom
of
its
travel.
,The gap betweeJ;l
the
ends
of
therlng
should
.beas
,
given intl1e
Table
of
Clearances.
Rings which
are
slightly
oversize
may
be
HIed
as
necessary
to
obtain
the
correct
gap,butdo
not
use
rings
which
require
too much filing. Standard
size
rings
may be used
on
a
.005"
oversize
piston. • 010", • 020"
,and.
030"
oversize
rings
are
to
be
used
on
.010",
• 020", and
:030"
oversize
pistons,
respectively.
Rings
of
the
tapered
type
are
usually
marked
"TOP"
on one Side,
or
identified
in
some
other
manner,
and the
ring
must
be
installed
with
this
mark
toward
the
closed
end
of
the piston. Space
each
ring
gap one
third
of
the
way around
the
piston
from
the
preceding
one, with
no
gap
directly
in line with
the
piston
pin. The bottom piston
ring
groove should
be
fit~
ted with
an
expander and an oil
control
ring
and
the
two upper grooves
,t"',
fitted with
compression
rings.
If
a
chrome
faced
ring
is
used, it will be
in
the
top groove. The oil control
ring
is
selected
for
best
performance
in
regard
to
the
correct
unit
pressure
characteristics.
,
The
piston
is
fitted with a .full floating type piston pin.
The
pin
is
kept
~'
in
place
by two lock
rings
in the piston, one
at
each
side.
Be
sure
these
'
lock
rings
are
properly
in
place
,before installing the
piston
and
connect-.
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