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16
Chapter I-General Engine Repair
the
heading "b. Piston
Pins."
Connecting rod inspection
is covered under the heading
lie.
Connecting Rods."
a. Pistons and Rings.
Pistons
and
rings seal the
combustion gases from
the
crankcase
and control
the
amount of oil
left on the
cylinder
wall for
lubrication.
Worn
or improperly
in~
stalled
rings will
cause engine
oil contamination, exces-
sive
oil
consumption,
fouled spark plugs, and poor
engine
performance.
Three types
of piston rings sets are
used in
servicing
Ford
engines.
They are: a
"snap"
type or
standard ring
set; an
dexpander"
type ring set; and a "steel
section"
type
ring set. Figure
23
shows the various
compression
and oil
control rings included
in
these ring
sets.
The
standard
or
snap
type ring is
designed
for use in
a new
engine
block
or
whenever a block is reba red
and
new
pistons
installed.
Under these conditions the block
would
neither
be
out-of-round
nor have
a
taper. A
light
honing
with
a
No.
280
grit hone
is recommended
in
either
case.
Under
a
tapered
condition
the
standard
type oil
rings
are not
flexible
enough
to provide sufficient wiping
action on
the cylinder
wall.
Oil is then
allowed
past
the
rings
and
oil consumption increases.
To remedy
this situation the
expander
type ring is
used in cylinder
bores where the taper does not exceed 0.006 inch or
whenever an oil consumption
condition is
encountered.
Ring pressure
is
maintained by
an expander
under the
oil ring.
Hone the
cylinder
bores before
installing
the
expander
type ring.
When the cylinder bore taper is greater than 0.006
inch but
less
than
0.015
inch,
the
expander
type ring
is
not
adequate
to
seal the combustion
chamber from
the
crankcase.
Under this
condition
the steel
section
type
ring
is
used.
The
oil
ring is installed
with
a steel
ring
on both
top
and
bottom in addition to the
expander
under the ring. Honing is not necessary
when
the
steel
section
type
ring.
is used.
(1)
CLEANING AND
INSPECTION.
Remove
all
carbon
from the piston with a scraper
or carbon
brush.
Clean the piston ring grooves with a ring groove
cleaner (fig. 24). Clean the carbon from the oil return
holes
in
the oil
ring grooves
by running
a
drill through
the holes.
Be
sure the drill is
the
same
size
as the hole.
Inspect pistons
for
fractures
at the ring
lands,
skirt,
and pin bosses. Replace pistons showing signs of wavy
ring lands, fractures,
or
damage
from detonation.
Spongy
eroded areas
around the top
edge
of the piston,
usually
on
the
side opposite
the valves, are
caused
by
detonation.
In
some
instances holes are
also
burned
through the top
of the
piston.
(2) INSPECT CYLINDER
BLOCK.
Make a thor-
ough
cheek for cracks. Minute cracks can be located
simply
and
quickly
with
the
following procedure: Coot
the
cylinder
wall with a
mixture
of 25 percent kerosene
and
75 percent light engine oil.
Wipe
the wall dry, then
apply
a light coat of zinc oxide powder
dissolved
in
wood alcohol.
The
cracks will show as discolored lines
on the
zinc
oxide
coating.
Inspect the cylinder bore for scratches or
scuffing.
Check for bulging at the top of the cylinder
bore.
Re-
place any
leaking
expansion plugs (indicated by rust
around the plug). Use a sealing compound under the
new
plug.
Check tbe cylinder bore using a telescope gauge and
outside micrometers,
cylinder
gauge, or inside microm-
eters.
Measure and record as
"A,"
"B,"
"C,"
and
"0
"
the dimensions shown in fig. 25.
Compare
"A"
with
liB"
and
"C"
with
"0
"
to determine
the
amount
of taper in the bore.
If
the taper
is
greater
than
0.015 inch, the
cylinder
must be
rebored.
Compare
IIA"
with
"C"
and
''H''
with
"0"
to deter-
mine
how
much the
cylinder
is out of
round.
If the bore
is more than 0.003
inch
out of round it must be re-
bored.
(3)
BORING CYLINDER
BLOCK. To assure
maximum performance and balance of the reciprocating
parts of the engine, all cylinders must be bored to the
same size
even though only one cylinder requires re-
boring and the others
are within
tolerance.
Manufac-
turers
recommendations on
how
to use boring equip.
ment
should
be followed and the work performed only
by
experienced
personnel.
Bore the most badly worn cylinder first to determine
the proper oversize. If the cylinders will not clean
up
at
0.060 inch oversize, the block must be
replaced.
When reboring the
cylinders
allow 0.0015 inch stock
for honing when fitting pistons. Use a number 220 to
280 grit hone
for
this operation.
CAUTION: Thoroughly clean
the
block to remove
all particle. of abra.ive after the honing operation.
Fig
.
24-Cleaning
Pislon Ring Grooves
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