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AERONCA Engine Handbook Table of Contents Previous Section Next Section Index Home
PART V - COMPLETE OVERHAUL - Continued P. Ignition System 1. Spark Plugs The spark plugs should be cleaned and carefully examined for cracks
and tested for leakage and firing. The plugs should fire uniformly,
at least up to 120 lbs. Of air pressure with a gap clearance of
.018". To clean aviation spark plugs remove all deposits from the
electrodes but do not use emery paper or cloth because emery is a
good conductor of electricity and will four the spark plug. When
adjusting the gap always bond the outer electrode - never the
center one.
It is very important to select a spark plug which has the correct
heat characteristics for the AERONCA engines. If a spark plug
operates at too low a temperature, it will foul up if the engine
is idled very long and it will also make a cold engine hard to
start as the spark plug does not operate warm enough to condition
the fuel around it on the compression stroke of the engine. If the
spark plug runs too hot or at too high a temperature the electrodes
will be burned and the engine will have tendency to pre-ignite.
When using a gasoline doped with Ethyl fluid, the electrodes of a
hot plug will have a lead deposit fused on them which in turn will
usually cause the failure of the plug. This does not occur when
using an Ethyl gasoline with a cool or correct heat plug. The
following spark plugs have been found to operate satisfactorily
in AERONCA engines: BG No. 4C, No. 4B-1, and Champion No. 13 in
the E-113, E-113A, E-113B, and E-113C; Champion No. 7 in the E-107A
engine.
2. Ignition Cables The high tension ignition cables to the spark plugs should be
examined for bad insulation, loose and corroded terminals and
should be replaced if found damaged.
The low tension ground cable and switch should also be examined
for bad insulation and poor connections. It is very important that
this circuit be in good condition electrically, otherwise the
ignition will always be partly "on" and the engine may start or
"kick" if someone accidentally turns the propeller through a
compression stroke.
3. Magneto and Impulse Coupling The Bosch FF2AR Magneto, Series S-531, is used on all AERONCA
engines. It runs clockwise at one-half engine speed and is equipped
with a type C-123 Bosch Impulse Coupling which is automatic in
operation and facilitates the starting of the engine in the manner
outlined below.
The impulse coupling is a coiled spring drive between the engine
and the magneto and has no effect on the magneto when the engine
speed is above 250 RPM. However, below this speed a catch or
"pawl" operating by centrifugal force locks the magneto armature
shaft allowing the coiled spring to wind up through a fixed angle
of rotation of approximately 20 when a trip releases the "pawl"
and the spring gives the armature a sudden twirl or acceleration.
It is this sudden acceleration of the armature that produces a hot
spark at the spark plugs and so makes starting easy. It can be
seen that it does not make any difference how fast the propeller
is turned when starting the engine as the impulse will operate in
the same manner each time, providing the engine speed does not
exceed 250 RPM. Above this speed the centrifugal force is
sufficient to hold the "pawls" out of engagement and so prevent
the impulse from operating.
This is the reason why it is possible to start AERONCA engines by
pulling the propeller through a compression stroke very slowly.
Hence, there is no necessity for trying to turn the propeller at
idling engine speed. If the engine does not start readily, then
one of the following conditions may be the cause:
a) Impulse coupling not working or working only on one cylinder.
This can be checked by listening for the click on each
compression stroke. If no click is heard, force some kerosene
into the impulse at the rear of the dust cover. Occasionally
in cold weather the oil in the coupling will prevent the
"pawls" from working.
b) Fouled spark plugs or improper gap clearance. c) Burned beaker points on magneto or improper gap clearance. d) Faulty wiring - corroded or loose connections. e) Worn Impulse "Dogs." Each time the impulse coupling operates,
the driver and driven members which have been separated some
20 by the coiled spring snap back together again. There are
two stops or "dogs" on each of these members which take this
impact load and they may have become worn enough to advance
the normal spark timing of the engine by 6 or more. When this
occurs, the impulse starting timing is retarded this same
amount. In other words, when starting, the spark occurs 6 or
more after T.D.C. instead of approximately on T.D.C. This
additional retarding of the spark makes the starting of the
engine more difficult and it should be corrected. (See Section
3-P-5 - TIMING THE MAGNETO for method of correction.)
NOTE: It is important to note that, regardless of where the manual or
automatic spark control is set, the starting spark will be
determined by the impulse coupling alone. This is due to the
fact that the time interval required to rotate the armature
through the 20 angle by the impulse spring is so very short
that the spark occurs directly after the trip releases the
armature shaft. Since this tripping off point is fixed, except
for the wear mentioned, the spark will always occur at the
same place.
However, the manual spark control must always be in the fully
retarded position when starting the engine. (This is taken care
of automatically on engines equipped with the automatic spark
control.) It is advanced, a bad kick may result because just as
the engine speed will have exceeded the 250 RPM limit and the
spark will occur at the advanced setting of the manual control.
f) Hard starting can also be caused by worn intake valve guides
in the cylinder heads. Although this does not concern the
electrical system it is of sufficient importance to be noted
here.
g) Periodic inspection of the collector brushes on the Bosch Magneto
will prevent a forced landing due to magneto trouble.
After some three hundred hours of operation, the carbon collector
brushes in the front end of the Bosch FF2AR Magneto may have
worn considerably although not always enough to require
replacing with new brushes.
However, the carbon dust from the brushes that collects in the
housing may be enough to cause the hi-tension insulation to fail
with the result that the magnet will fire irregularly or even
quit cold.
The carbon dust will also increase the tendency of the hi-
voltage to arc from the commutation segment to the brush and
so cause pitting of the segments. If the pitting is bad, it
will be necessary to resurface the segments. Use a piece of
very fine sandpaper such as No. 8/0 or finer.
The collector brushes should be inspected at every complete
engine overhaul.
When removing the collector brushes, it is best to first remove
the hi-tension cables from the spark plugs at the magneto
terminals. The early Bosch FF2AR magneto had cable terminals
that snapped into place. All later models have threaded
terminals.
By removing the single cap screw between the two terminals, the
entire cover and two brush assemblies can be removed. The entire
assembly should come out of the housing with little or no effort.
Do not pry on the brush holders as they are rather brittle and
may break.
If the pitting is bad, use a piece of fine sandpaper, as
suggested above, and with a light pressure clean off the
commutation segments. Be sure to clean out all of the small
particles of metal and foreign matter before reassembling the
brush unit.
If it is necessary to renew the carbon brushes, care must be
taken to see that the offset part points towards the steel
springs and that the carbon brush is pushed in until the steel
spring catches. When replacing the carbon holders in the
apertures, see that the carbon brushes slide freely into the
recesses provided, otherwise they will be damaged.
h) The breaker points on the Bosch magneto should be set to break
30 B.T.C. on the AERONCA E-107A engines and 36 B.T.C. on the
E-113, E-113A, E-113B and E-113C engines with the spark fully
advanced. These are the maximum recommended spark settings and
must not be exceeded.
4. Magneto Timing Marks on Crankcase and Propeller Hub. All AERONCA engines after Serial No. A-743 have the T.D.C. (0)
and 36 spark advance marks stamped on the front end of the
crankcase with a reference mark on the propeller hub. These marks
greatly facilitate the timing of the magneto and can be placed on
any AERONCA engine by following the method outlined below:
a) Assume an arbitrary location on the front end of the crankcase
for T.D.C. (0), preferably on the vertical line through the
crankshaft. (See Figure 4-A below) Mark with a sharp tool.
b) Lay off the scale given in Figure 4-B from the corresponding
T.D.C. (0) mark on the crankcase in a direction opposite to
the rotation of the propeller. Mark only the correct spark
advance angle for the engine; i.e., 30 for the E-107A and 36
for the E-113 and E-113A, B & C.
c) Turn propeller until No. 2 cylinder (left) is on its compression
stroke (both valves closed) and pistons are on T.D.C. Then mark
the propeller hub directly opposite the T.D.C. (0) mark on the
crankcase. The T.D.C. position can be found by inserting a steel
ruller or rod through the spark plug hole and noting the
location of the piston. Take particular care in locating T.D.C.
d) There will now be two marks on the crankcase; i.e., T.D.C.
0 , 30 or 36 , the spark advance angle, and one reference
mark on the propeller hub.
5. Timing the Magneto The magneto timing should be checked at least every 100 hours of
flying. To do this proceed as follows:
a) Disengage the impulse coupling on the magneto by removing the
set screw at rear of the dust cover and rotating the cover in
the direction of rotation of magneto until a stop is reached.
The magneto will now be on direct drive with the engine.
b) Set the magneto breaker points to the correct gap (.015"). Use
the special Bosch magneto wrench and feeler gauge. The points
should be smooth and free from oil.
c) Set the magneto in the full advance position. Check the cam
housing ring on the magneto to see that it is tight against its
stop or the magneto will not be fully advanced.
d) Turn the propeller until No. 2 cylinder (left) is on its
compression stroke and the mark on the propeller hub is about
opposite the 50 B.T.C. position on the crankcases.
e) Place a strip of cigarette paper between the breaker points and
rotate propeller slowly in normal direction until the paper will
just pull.
f) Then note the position of the mark on the propeller hub. It
should be very close to the 30 or 36 advance mark on the
crankcase, depending upon which engine is being timed.
g) Reset the impulse coupling and lock the dust cover with the set
screw.
IMPORTANT Should the magneto timing be found to have advanced a considerable
amount over the normal setting, the chances are that the "dogs" in
the impulse coupling have worn. There are two alternatives to
follow to reset the timing back to normal:
Remove the gear cover and reset the idler gear which drives
the magneto, being careful not to change the relation between
the crankshaft and camshaft gears or the valve timing will be
out. The pistons must be on T.D.C. when this is done. It is
not advisable to do this if the spark has advanced more than
6 as the impulse coupling will be retarded this additional
amount and hard starting will result.
The other method is to renew the "dogs" (Park ZKR 5/4) in the
impulse coupling. This should immediately set the spark back to
normal and give the correct impulse timing on starting. The
magneto should be returned to the factory for repair.
6. Irregular Running of AERONCA Engines at Full Throttle Occasionally an AERONCA engine will develop a very distinct knock,
or detonation thump, accruing at irregular intervals which can be
felt throughout the fuselage. This may occur only once or twice
during a take-off and usually at full throttle operation. This
trouble will be found to be due to a weak spring on the breaker arm
in the magneto. By increasing the spring tension the trouble will
stop.
To make breaker spring adjustment (See Figure 6-A) (a) Remove breaker mechanism by first removing cap, control arm,
cam housing ring and center screw.
(b) On the breaker mechanism, remove one of the screws holding the
flat springs and bend the short inner springs, (Figure 6-A), a
very slight amount outward so that a force of 3 lbs on the
fiber block applied radically inward will just separate the
breaker points. This force must not be less than 3 lbs, nor
more than 3 1/2 lbs. Be very careful in bending the springs (S)
as it will not require very must bending to give the required
spring tension. A small spring scale may be used to check
the spring tension.
(c) When assembling the breaker mechanism, see that the long flat
spring does not touch the cams or cam housing ring when the
magneto armature is rotated. This is important.
(d) When connecting the manual spark control (if used), set the
magneto cam housing ring in the full advanced position, then
push the manual spark control all of the way "in" and back it
out about 1/4". Connect the control arm to the magneto in this
position. This will always insure the magneto being set in the
full advanced position when the manual spark control is pushed
all of the way "in."
(e) Only an experienced mechanic should attempt to make this
adjustment. If desired, the breaker mechanism may be returned
to the factory for adjustment or to any Bosch Service Station.
TDC 0 1-19/32" = 30 BTC Use 30 for E-107A 1-15/16" = 36 BTC Use 36 for E-113, A,B &C Scale: 1" 18.8 FIGURE 4-B TIMING SCALE FOR ALL AERONCA ENGINES 7. The Automatic Spark Control This automatic spark control does away with the manual spark
control. The installation is shown in Figure 12 at the rear of the
book. It consists of a lever system connecting the magneto arm to
the carburetor throttle arm in such a manner as to always retard
the spark when the throttle is closed. It will automatically
advance the spark as the throttle is opened. This device affords
the following advantages:
(a) It will prevent a take-off with a retarded spark. (b) It is positive in operation. (c) It reduces the stresses imposed on the engine when idling,
as the spark will always be retarded.
(d) It allows a slower engine speed when coming in for a landing. (e) It gives much smoother engine operation. This device can only be used on AERONCA engines equipped with the
Zenith Carburetor No. 156 AL or Stromberg NAS-2 carburetor. This
includes all of the engine on the AERONCA C-3 airplanes.
Q.1 Carburetor - Zenith 156AE The Zenith 156AL carburetor differs from the standard 156 series
carburetor in that it has a special aluminum alloy body. The carburetor
should be completely disassembled, cleaned and all parts checked for
wear. This work should only be done by an authorized Zenith Service
station or by the factory, inasmuch as it is necessary to remove
numerous jets and other small parts which require special tools.
The carburetor is taken apart by removing the two cap screws which
hold the top and bottom castings together. It is very important to
remember that the small holes in the jets can be greatly enlarged if
a wire is used to clean the jets. The jets should be cleaned in
gasoline and blown out with compressed air. After all parts have been
thoroughly cleaned they should be examined for wear.
The upper piston on the vacuum pump (see carburetor data at rear of
this book) should not have more than .003" clearance in the cylinder
in the upper casting. If it is more than this, the entire vacuum pump
(Part No. D-6366) should be replaced as worn piston will cause the
engine to back-fire and be rather sluggish when the throttle is opened
suddenly. This is due to the vacuum pump not supplying sufficient
gasoline to the engine to take care of the additional acceleration.
The float level should be checked from time to time and should be 5/8"
below the top edge of the fuel bowl.
If the engine does not idle properly or run steady between 400 and 450
RPM with the spark retarded, there is a possibility that this is being
caused by a worn throttle plate (Part No. D-5564). Examine the throttle
plate and shaft especially at the bearings at either side of the plate.
If, when the throttle plate is closed, there is any noticeable wear,
especially near the two bearings, the throttle plate should be
replaced. It is usually necessary to replace the shaft, if it is worn
in the bearings. To replace these parts remove the two throttle plate
set screws (Part No. D-3493) and the throttle plate. The throttle
shaft (Part No. 6455) can then be taken out after one end fitting
has been removed. The throttle lever stop (Part D-6463) is attached
to the shaft by a taper pin (Part No. C-42x22). When assembling the
new throttle plate, it may be necessary to fit it to the present
bore of the carburetor. The two set screws should be staked after
they are tightened.
It is very important that the body to bowl assembly gasket (Part No.
C-4517) be in good condition so that there will be no leakage by it.
It is important to note that this gasket differs from the standard
Zenith Carburetor gasket in that it has a special hole in it over
the ball check valve and is made especially for this carburetor. If
a standard gasket is purchased from a Zenith service station, compare
it with the old gasket and cut this additional hole in it, otherwise
the carburetor will not function properly.
After reassembling the carburetor, the idling screw should be opened
between 1 and 1-1/4 turns. To get the current idling speed, between
400 and 425 RPM with the spark retarded, adjust the stop on the
throttle lever and not the idling adjustment screw. The correct
setting for the main jet is between 1 1/8 and 1 1/4 turns open.
When installing a carburetor to the intake manifold on the engine,
be very certain that the small air bleed hold in the flange of the
carburetor does not leak through the gasket. This small hole is
directly beneath the countersunk screw which attaches the adapter
plate to the intake manifold. It is advisable to cut several pieces
of gasket material to fit into this countersunk hold in the adapter
plate so that there will be no chance for leakage.
Following are the sizes of the various jets and other parts used in
the Zenith 156 AL Carburetor on the E-113, E-113A, and E-113B engines:
No. 27 Venturi No. 11 Idling Jet
No. 25 Main Jet No. 12 Power & Accelerating Jet
No. 54 Fuel Valve Ass'y No. 23 Gap Jet
No. 25 Compensating Jet
If short exhaust stacks are used with an air cleaner on the carburetor
intake, it may be necessary to use a No. 13 Power and Accelerating Jet
in order to take care of the loss of heat at the carburetor.
Q.2 Carburetor - Stromberg NAS-2 (See instructions at rear of book).
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