Cessna T188C - Magneto Check; Spark Plugs

MODEL
188 & T188
SERIES SERVICE
MANUAL
a. Moisture
Check.
c. Advance
engine
speed to 1700
rpm.
1. Remove magneto
from engine and remove
d. Turn the ignition
switch to the "R" position and
screws securing the magneto halves together, dis- note the rpm drop, then return the switch to the
connect capacitor
slip terminal and remove
distrib- "BOTH" position
to clear the opposite set
of plugs.
utor. Inspect for moisture. e. Turn the switch to the "L" position and note the
2. Check
distributor gear finger and
carbon rpm drop,
then return the switch to the
"BOTH"
brush
for moisture.
position.
3. Check
breaker
point assembly
for moisture,
f. The
rpm drop should
not exceed
150 rpm on
especially
on
the surfaces
of the
breaker points.
either
magneto
of show
greater than
50 rpm
differ-
4.
If any moisture
is evident
in
the preceding
ential
between magnetos.
A smooth
rpm drop-off
places,
wipe with
a soft,
dry, clean,
lint-free
cloth.
past normal
is usually
a sign
of a too
lean or
too
b.
Breaker Compartment
Check.
rich
mixture.
A sharp rpm
drop-off
past normal
1. Check
all
parts
of the breaker
point assem-
is
usually
a sign
of a fouled
plug,
a defective
harness
bly for
security.
lead
or a
magneto
out of
time. If
there
is doubt
con-
2. Check
breaker
point surfaces
for
evidence
cerning
operation
of the
ignition
system,
rpm
checks
of
excessive
wear,
burning,
deep
pits and
carbon
at a leaner
mixture
setting
or at
higher
engine
speeds
deposits.
Breaker
points
may be
cleaned
with a
will
usually
confirm
whether
a deficiency
exists.
hard-finish paper.
If breaker
point assembly
is de-
fective,
install
a new
assembly.
Make
no attempt
NOTE
to stone or dress the breaker points. Clean new
breaker
points
with
clean,
unleaded
gasoline
and
An absence
of rpm
drop
may
be an
indication
hard-finish
paper
before
installing.
of faulty
grounding
of one
side
of the
ignition
3. Check
capacitor
mounting
bracket
for
cracks
system,
a disconnected
ground
lead at
mag-
or looseness.
neto
or
possibly
the
magneto
timing
is set
4.
Check the
carbon
brush
on the
distributor
too
far in
advance.
gear for excessive wear. The brush must extend a
minimum
of 1/32
inch beyond
the end
of the gear
11-63.
SPARK
PLUGS.
Two spark
plugs are
in
shaft.
The
spring
which the
carbon
brush
contacts
stalled
in each
cylinder
and
screw into
helicoil
type
should
be bent out
approximately
20 degrees
from
thread inserts.
The
spark plugs
are shielded
to pre-
vertical, since
spring pressure
on the brush
holds
vent spark plug
noise in the radios
and have an
inter-
the distributor
gear shaft
against the thrust
bearing
nal resistor to
provide longer
terminal life. Spark
in the
distributor
cap.
plug
service
life
will vary
with
operating
conditions.
5. Oil
the bearings
at each
end
of the
distributor
A spark
plug
that
is kept
clean
and
properly
gapped
gear
shaft with
a drop
of SAE 20
oil. Wipe
excess oil
will
give better
and longer
service
than one
that is
from parts.
allowed to collect
lead deposits
and is improperly
6.
Make
sure
internal
timing
is
correct
and
re-
gapped.
assemble
magneto.
Install and properly
time mag-
neto to engine.
NOTE
11-62.
MAGNETO
CHECK.
Advanced
timing
set-
At each
100 hour inspection,
remove,
clean,
tings in some
cases, is the
result of the
erroneous
inspect
and regap all
spark plugs.
Install
practice
of bumping
magnetos
up in
timing in
order
lower
spark
plugs in
upper portion
of cylin-
to reduce
RPM drop
on single
ignition.
NEVER
AD-
ders
and install
upper
spark plugs
in lower
VANCE
TIMING
BEYOND
SPECIFICATIONS
IN
OR-
portion
of cylinders
at
each 100
hour inspec-
DER
TO REDUCE
RPM DROP.
Too
much
impor-
tion. Since
deterioration
of lower
spark
plugs
tance
is being
attached
to RPM
drop
on
single
ignition.
is
usually
more
rapid
than
that
of the
upper
RPM
drop
on single
ignition
is a
natural
character-
plugs,
rotating
them
helps
prolong
spark
plug
istic
of dual
ignition
design.
The
purpose
of the
fol-
life.
lowing
magneto
check
is to determine
that
all cylin-
ders
are
firing.
If all cylinders
are
not firing,
the
11-64.
ENGINE
CONTROLS.
engine
will
run extremely
rough
and cause
for investi-
gation
will be
quite apparent.
The
amount
of RPM
11-65.
DESCRIPTION.
The throttle
and propeller
drop is
not necessarily
significant
and
will be
influ-
governor
control
levers
are in the
control
quadrant
enced
by
ambient
air temperature,
humidity,
airport
mounted
to
the left
of the pilot's
seat.
The
mixture
altitude,
etc.
In fact,
absence
of RPM
drop
should
control
is
equipped
with
a position-locking
device
be
cause
for suspicion
that
the magneto
timing
has
which
prevents
vibration-induced
"creeping"
of the
been
bumped
up and is set
in advance
of the
setting
control.
The carburetor
heat control
is located
on
specified.
Magneto
checks
should
be performed
on a
the lower
left
side
of the
instrument
panel
and has
comparative
basis
between
individual
right
and
left
no
locking
device.
On
later
model
aircraft,
an
addi-
magneto
performance.
tional
"Palnut"
type
locknut
was
installed
in
back
of
a. Start
and run
engine
until
the oil and
cylinder
the
existing
locknut
at the
engine
end of
all throttle
head
temperature
is
in the
normal
operating
range.
and
propeller
controls
that
contain
rod ends.
b. Place
the
propeller
control
in
the full
low pitch
(high
rpm)
position.
11-21