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18
Chapter I-General Engine Repair
Table 7-Ring Groove Clearance Specifications
H
M
Rings
Upper Compression
0.0015-0.0030
0.0015
-0.0030
Lower Compression
0.0010-0 .0025
0.0010-0.0025
Oil Rings
0.0010-0.0025
0.0010-0 .0030
able
clearance,
place
a
piece
of emery cloth on a
fiat
surface and rub the
ring
on
the
emery cloth
in
a circular
motion. Rotate
the
ring while
rubbing to
maintain uni-
form ring thickness.
If
several
rings
are
found to have
greater
than the
mllximum
allowable clearance, the
piston
should be
replaced.
NOTE: When the steel section OHA ring
sets are
not
available for H
&eries engines,
the
steel section 7HA
ring. may be used on the OHA piston by installing
the oil ring
expander
in
the
third
groove
rath
e
r
than
in
the fourth
groor;e
as
specified
on
the
THA
pistons.
h. Piston Pins.
Ford engines use hollow piston pins held in the
piston by
wire retainers at
both
ends of
the pin. Piston
pins
are available in 0.001
and
0.002 inch
oversizes
for use when
a standard
pin fits too loosely.
(1)
INSPECTION. Replace piston pins
showing
signs of fractures
or
etching.
Worn piston pins
or
pins
that fit loosely in the
piston
or rod bushing
should
be
replaced. Replace
all
piston pin retainers.
(2)
FITTING PISTON PINS. Check the piston pin
fit
in
the piston pin bore
at
normal room temperature
Fig.
27-Checking Ring Groove
Clearance
Engine
R
E
8MTH
8EQ
Piston
Piston
0.0015-0.0030
0.0015-0.0030
0.0020-0.0040
0.0010-0.0025
0.0010-0.0025
0.0015-0.0030
0.0010-Q.0030
0.0010-0.0025
0.0015-0.0030
(70
'
F.). Table 8
gives
the proper piston pin fit
for
each
engine.
If
oversize
piston pins
are
used, or if the piston pins
are too
tight, use
an expansion
type piston pin reamer.
Place
the reamer in a vise and
revolve the piston
around
the reamer
(fig.
28)
.
Set the reamer to the
size of
the piston pin bore,
then
expand
the reamer
slightly and
trial ream the
bore
'/8
inch deep
in the piston. Use a pilot
sleeve
of
the
nearest size
to maintain
alignment of
the piston pin
bores.
Check
the reamed
hole size using
a
new piston pin
as a gauge.
If the bore is too
small,
finish
reaming
the
hole, then turn the
piston
around and ream the other
hole.
Expand the reamer
slightly
and make another trial
cut, then
repeat the procedure outlined until the desired
pin fit is obtained.
Table 8-Piston
Pin Fit Specincations
Clearance
in
Clearance in
Engine
Piston (Inches)
Connecting Rod
Bushing
(Inches)
H
0.0001-0.0003
0.0001-0.0003
R
0.0001-0.0003
0.0001-0.0003
E
0.0001-0.0005
0.0001-0.0002
M
0.0001-0.0002
0.0001-0.0003
Fig. 28-Reaming
Piston Pin
Holes
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