'Jeep'
UNIVERSAL
and
'Jeep'
DISPATCHER
D
D-32. Cylinder Bores
The
cylinder
bores
may
be
reconditioned
by
honing
or
reboring.
Use
oil-soaked
rags
to
protect
crank-
shaft
journals
and
other
engine
parts
from
abrasive
dust
during
all
reconditioning
operations.
Both
honing
and
reboring
of
the
cylinders
must
be
done
carefully
to
fit
the
pistons
and
to
obtain
specified clearances.
If
reboring
of
the
cylinder
bores is
not
required
but
the
walls
are
glazed,
use
a finishing
hone
to
remove
the
glaze.
Reboring
the
cylinders
must
not
be
attempted
unless
ade-
quate
facilities
and
experienced
service
technicians
are
available.
The
amount
of
material
to
be
re-
moved
is
determined
from
the
original
diameter
of
the
cylinder
bores
(3.125"
to
3.127")
[79,375 a
79,426 mm.]
plus
the
amount
of
oversize
in
diameter
of
the
oversize
pistons
to
be
fitted.
Pistons
are
available
in
the
following oversizes.
.010" [0,254 mm.] .030" [0,762
mm.]-
.020" [0,508 mm.] .040" [1,016 mm.]
The
largest
cylinder
bore
will
determine
the
over-
size
to
which
all
cylinders
must
be
rebored,
since
the
size
and
weight
of
all
pistons·
must
be
uniform
to
maintain
proper
engine
balance.
The
maximum
rebore
should
not
exceed .040" [1,016 mm.]
from
standard.
Measure
the
cylindrical
diameters
by
making
mea-
surements
both
parallel
to
and
at
right
angles
to
crankshaft
over
entire
piston
travel
and
at
bottom
of
cylinder.
Proceed
as
follows:
a.
If
bores
are
scored;
if
out-of-round
exceeds .005"
[0,127
mm.];
if
diameters
differ
more
than
.005";
or
if
taper
exceeds .005"
on
diameter,
it
is
generally
recommended
that
cylinders
be
reconditioned
by
reboring
and
honing
to
the
next
oversize
using
new
pistons
of
the
proper
size.
NOTE:
If
reboring
is
performed,
allow .0015"
[0,0381 mm.]
for
final
honing.
All
cylinder
bore
diameters
must
be
within
.002"
[0,0508
mm.]
after
reconditioning.
b.
If
bore
measurements
are
within
the
above
limits,
but
indicate
hollows
or
waviness,
cylinders
should
be
honed
with
250
grit
stone
hone.
Pump
hone
up
and
down
in
cylinder
while
it
is
rotating
to
produce
a satincfinish,
diamond
cross-hatched
pattern
approximately
30°
with
horizontal.
Hone
only
enough
to
correct
waviness.
c.
If
cylinder
bore
correction
is
unnecessary,
break
the
glaze
on
cylinder
walls
with
a 250
grit
stone
hone
or
with
a
suitable
deglazing
tool.
Operate
the
hone
or
deglazer
to
obtain
diamond
cross-hatched
pattern
previously
mentioned.
d.
Regardless
of
type
of
correction
on
cylinder
walls,
wash
out
bores
thoroughly
afterwards
and
apply
a
light
coat
of
engine
oiL
If
cylinders
have
been
rebored
or
honed
heavily,
measure
cylinder
diameters
again
to
assure
proper
selection
of
piston
size.
D-33. Pistons, Rings, and
Connecting
Rods
Pistons
are
each
fitted
with
two
compression
rings
and
one
oil
control
ring.
Pistons
have
an
extra
groove
above
the
top
rit1g
which
acts
as
a
heat
dam
or
insulating
groove
to
protect
against
sealing
of
the
top
ring
in
the
ring
groove
with
hard
carbon.
The
piston
pin
is
secured
by
a lock screw.
The
pistons
and
connecting
rods
were
removed
from
the
engine
as
assemblies.
If
cylinders were rebored,
new
oversized
pistons
and
rings will
have
to
be
in-
stalled.
Use
standard
size
pistons
in
cylinder bores
up
to
.009" [0,2286 mm.] oversize
measured
at
the
bottom
of
the
bore.
For
oversize, use
the
following
chart:
OVERSIZE
PISTON
APPLICATION
CHART
Oversize
Use
in
Oversize
Metric
Piston
Cylinder
Bore
Range
.010"
.010"
to
.019"
0,254 a 0,438
mm
.
.020"
.
020"
to
.029;,
0,508
a 0,737
mm.
.030"
.030"
to
.039"
0,762 a 0,991
mm.
.040"
.040"
1.016
mm.
Disassemble
the
pistons
and
rods.
Remove
the
two
compression rings,
the
oil
control
ring,
and
the
oil
control
ring
expander
from
each
piston.
Do
not
remove
the
bolts
from
the
lower
end
of
the
connecting
rods
unless
the
bolts
are
damaged.
Clamp
each
connecting
rod
and
piston
assembly
in
a
padded
bench
vise
and
remove
the
piston
pin
lock
screw
and
lockwasher.
Press
the
piston
pin
out
of
the
piston
and
connecting
rod.
Clean
all
carbon,
gum,
and
lacquer
deposits
from
both
the
inner
and
outer
surfaces
of
each
piston,
connecting
rod,
and
piston
pin.
Use a
ring
groove cleaner
or
a
broken
ring
filed
to
a
sharp
square
edge
to
clean
the
carbon
from
the
piston
ring
grooves
and
the
insulator
groove.
Use
care
not
to
scrape
metal
from
the
sides
of
the
grooves
or
make
burrs
on
ring
groove surfaces.
Run
a
length
of
wire
through
the
oil
spray
hole
near
the
lower
end
of
the
connecting
rod
to
clear
the
hole
of
hardened
oil
deposits
or
foreign
matter.
Carefully
inspect
the
pistons
and
replace
any
that
are
broken
or
cracked. Replace
pistons
if
any
of
the
ring
lands
are
chipped,
broken,
or
rounded
on
the
edges;
or
if
the
piston
is
scored,
scratched,
or
burned
so seriously
that
the
imperfec-
tions
cannot
be
removed
with
a
hand
honing
stone
or
crocus cloth. ·
NOTE:
Effective
with
engine
S/N
50705,
the
piston
head
thickness
was
increased
from
%;
"
to
74:"
[4,
76
a 6,35 mm.]
~o
provide
greater
strength
and
heat
conductivity.
When
replacing
pistons
singly
or
in
sets,
procure
the
correct
parts
or
engine
vibration
will
result
from
unbalanced
pistons.
Replace
the
pistons
as
follows:
a.
After
cylinder
bores
have
been
carefully checked
for
out-of-round
and
taper
(Par.
D-32),
check
fit
of
each
piston
to
cylinder
bore
with
block
and
pistons
clean
and
dry
and
·at
approximately
70°F.
[21
°C.]
by
using
Piston
Fitting
Gauge
And
Scale
tool
C-690
as
shown
in
Fig.
35. Use· a .003" [0,076
mm.]thickness
gauge~"
[19
mm.] wide.
The
piston
is
fitted
.upside
down
in
the
block
to
facilitate
the
operation.
The
gauge
must
extend
the
full
length
of
the
piston
ori
the
thrust
side
(opposite
side from
slot
in
piston
skirt).
Scale
should
register
5
to
10
pounds
[2,3 a 4,5 kg.)
pull
to
remove
the
thick-
ness
gauge
from
between
cylinder
wall
and
piston.
Excessive
pull
indiqites
need
for a
slightly
smaller
33
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