Operator`s manual
OVERHAUL
MANUAL LYCOMING
DIRECT
DRIVE
AIRCRAFT
ENGINES
Section 6
Cylinders,
Pistons,
and Valve Train
-
Figure
6-15.
Method
of Checking
Valve
Edge
Thickness
with
Dial
Indicator
of
hours
onthe valve.
(See
inspection
of
hydraulic
tap-
pets.
) Check
the
clearance
between
the
valve
stem
and
guide
(reference
528,
Table
of Limits
for exhaust
valves,
and
reference
529
for
intake
valves).
6-43.
HYDRAULIC
TAPPET
BODIES.
If for
any rea-
son
a new
camshaft
is to be
installed
in the
engine,
or
the
cam
lobes
are
conditioned
by regrinding,
all
of the
tappet
bodies
must
be
discarded
and replaced
with
new
tappet
bodies.
6-44.
Checkthe
tappet
bodies
for
identification.
Those
bodies
with
no
identification
marks
as
shown
infigure
6-16 must
be discarded.
6-45.
Check
the
face
of the
tappet
body
for
signs
of
spallingor
pitting
(figure
6-17).
Any
face
whichshows
this
condition
is
cause
for
rejection,
and
the tappet
body
must
be replaced
with
a new
tappet
body.
It
is
recommendedthat
a
magnifyingglass
(min.,
10power)
be used
for
this
purpose.
6-46.
When
a
tappet
body
is rejected
because
of
spal-
ling,
a visual
inspection
of
the
nose
of the
cam
lobe
with
a magnifying
glass
(min.
10
power)
must
be
made.
Figure
6-17.
Appearance
of Spalling
Marks
on
Face
of Hydraulic
Tappet
Bodies
Any
indication
of distress,
surface
irregularity
or
featheringat
the edge
of
the
lobe
is cause
for
rejection
of
the camshaft.
NOTE
Each
tappet
face
will have
one
or
two
Rockwell
marks
(figure
6-18)
which
is
not
cause
for
rejection,
and
this
is
notto
be
confusedwith
a
spalled
or pitted
condition
as shown
in figure
6-17.
6-47.
Circular
wear
patterns
on
the face
of
the
tappet
body
are
also
cause
for
rejection
of the
part.
Each
face
may
have
circular
discoloration
due
to rotation
of
the
body
which
is not
cause
for rejection,
however,
if
the
surface
has
a wavy
appearance
the part
should
be
rejected
(figure
6-19).
6-48.
Examine
the
interior
of the
bore
in the
tappet
body
using
a small
flashlightto
illuminate
the interior
surfaces.
If
any
appreciable
amount
of
wear
has oc-
cured
at
the interior
shoulder
(which
serves
as
a seat
for
the
plunger
assembly)
a
feather
or chipped
edge
will
be
visable
around
the
shoulder
(figure
6-20).
The
existence
of this
feather
or
chipped
edge
is
cause
for
rejection
of the
entire
tappet
assembly.
6-49.
Test
the
tappet
body
for
structural
failure
through
the
use
of the
magnetic
particle
method.
This
requires
a machine
(which
uses
440
line
volts),
a cop-
per
adapter
and
a holding
fixture
ST-387.
The tappet
bodies
are inspected
in the
following
manner:
a. Clean
the
edge
of the face
with
medium
grade
sandpaper
and
any Ferrox
coating
(figure
6-22).
b. Placethe
tappet
body in
the holding
fixturewith
the
adapter
inserted
in the
body.
GROOVE
UNDER HEAD
PIMPLES
UNDER
HEAD
I-GROOVE 2-GROOVE
UNDER CUT DOUBLE
RIB
Figure
6-16.
Identification
of Hydraulic
Tappet
Bodies
Revised
October
1974
6-11