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Section 4-Connecting Rods, Pistons, Rings, and Pins
17
Table 6-Pis'on Fitting Specifications
H
Piston
T
y~
7HA
New Piston
in
New Bore
Gauge Thickness
(Inches)
0.003
Pounds Pull
6-12
New Piston
in
Used Bore
Gauge Thickness {Inches}
0.003
Pounds Pull
6-12
Used Piston
in
Used Bore
Gauge Thickness
(Inches)
0.003
Pounds Pull
6-12
(4)
FITTING PISTONS.
Proper
assembly
toler-
ances of
pistons
are
required
if
sa
tisfactory
engine
operation is
to
be
obtained.
Cylinder bores
must be
checked
for taper
and out-of-round condition
before
fitting a
piston.
To
install a
piston with
ne
w rings
in a
used
bore,
the high polish on the
cylinder
bore must
be
removed
to allow
the new rings to
seat without scuffing.
This is
done
by
running a hone through
the cylinder bore.
Clean the
cylinder
thoroughly to remove the hone dust.
To fit a new piston in
a
new
bore, aUaen a
tension
scale
to the end
of
a feeler ribbon
1
/2
inch wide
and
having the correct feeler
ribbon
thickness
as given
in
Table 6. Position the feeler ribbon
on
the thrust
side
of
the
cylinder
(right-hand
side of cylinder
bore
as
viewed
from the driver's
seat).
Invert the piston,
"
C"
AND
"
0
"
MEASUREMENTS
"A"
AND
" B"
MEASUREMENTS
MADE ACROSS ENGINE
MADE PARAllEl TO ENGINE
AXIS
REAR
00
FR
O
NT
TOP
OF
\LOC~EASUREMENTS
" A"
AND
"C
MADE BELOW
-.1
RIDGE OR AT THi TOP OF
RING TRAVEL
,-
I
MEASUREMENTS
"
B"
AND
" D"
MADE
AT BOnOM OF RING
TR
AVEl
Fig.
25-Cylinder
Bore
Measurements
1176
Engine
R
Piston
T
ype:
M
and
E
OHA
49T
-
BBA
0.002
0.003
0.0015
0.0015
3-12
6-12
3-12
5-10
0.002
0.003
0.0015
0.0020
3-12
6-12
3-12
5-10
0.003
0.004
0.003
0.003
3-12
6-12
3-12
5-10
then push
the piston into the
cylinder
bore until the
skirL is about
'/2
inch
below the top
of
the block. Keep
the piston pin bore parallel
with
the camshaft. Pull
out
the
feeler
gauge and
at the
same
time note the read-
ing
(fig.
26).
The
pull
limits for new pistons and used pistons in
new
or
used
bores
is
given in
Table 6.
(5)
FITTING PISTON RINGS. Insert the ring in
the
cylinder bore.
Invert
a piston and
use it to push
the
ring about
half
way down
into the bore. This
will
also square
the ring
with
the bore. Measure the ring
gap.
It
should
be 0.007
to
0.047 inch in a worn
cylinder.
If the
gap is smaller
than 0.007 inch, file the
ends of
the ring
until
the correct
clearance is obtained.
If the ring
gap exceeds
0.047 inch install the next
oversize ring.
Be
sure to
identify
the
rings
so
they
will
be
installed
in the
same cylinder
in
which they were
fitted.
Check
the
ring groove clearance on
the proper piston
for
the
cylinder
as shown
in fig. 27.
The
rings
should have the clearance shown in Table
7.
To
relieve
rings
with
less than
the minimum
allow-
Fig. 26-Fi"ing Pis'on
' 0
Cylinder
Bore
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