B
ENGINE
SECTION
821
REMOVING
AND
REPLACING
THE
PISTON
RINGS
There
should be little difficulty
In
removing piston
rings,
If
the
following
procedure
Is
adopted.
lift
one
end
of
the
top
piston ring
out
of
the
groove
and
Insert
a
thin
steel scrip between
the
ring and piston
Move
the
strip
round the piston, Insert a second and
then
a third strip,
as
shown
In
Fig.
B22.
The
rings
should
always be lifted offand replaced
over
the
top
of
the
piston.
Fig. 822. Piston ring
removal
If
the
piston rings are
to
be refitted,
the
carbon
deposits
on
the
Inside of the rings, and
the
deposits
in
the
ring grooves, must
be
removed.
When
fitting new piston rings,
the
bores
mUst be
lightly honed with a fine-grade
emery
cloth so
that
the
new
rlng·s
can
become bedded down
properly.
The
honing should be carried
out
with
a
combined
oscillatory
and reciprocating motion until an
even
"criss-cross" pattern
Is
achieved. The recom-
mended
grade
of
emery cloth
for
this
purpose
Is
No.
300.
Thoroughly
wash
the
bores
In
kerosene
(paraffin) and check that
all
traces
of
abrasives
are
removed.
Pistons and rings are available 'In ·.010, .020, and
·040 inches (.254, ·508 and ·1·016
·mm)overslzes.
When
fitting new rings,
the
gap ·must
be
checked
In
B24
the
lowest
part
of
the
cylinder bore. The ring must
lie
.square
to
the
bore
for checking purposes, and
to
ensure this, place the piston crown
onto
the
ring and ease
it
down che bore. Check
the
gap with
feeler
gauges.
Piston rings,
when
new, should have
the
following
gap clearances:
Compression
ring gap: .009/.013 In. (·2286/
·3302
mm.)
The
gap
for
the
'APEX'
type
scraper ring may be
quite
large
without
harmful effect (up
to
approx.
·040 In.)
Refitting
the
piston rings
Is
straight forward,
but
check
that
the
twO
compression rings
are
fitted
the
right
way up.
These
two
rings are marked
IITOP"
to
ensure
correct
assembly, and should
be
fitted
with
the
"TOP"
marking
towards
the
cylinder head (see
Fig.
B23).
Fig. 823. Refitting a
ta-p'ered
piston ring
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