AERONCA Memo M-34

June 1939                    PART II                    M-34
                                                        Page 1

MEMORANDUM TO OWNERS OF AERONCA E-113-CD AND E-113-CBD ENGINES.

Subject:  - Checking and restting the magneto timing.

                         EXPLANATION

    The dual ignition unit as installed on the Aeronca engines listed
above consists of an accessory containing two Robert Borsch Model
FF2AL mannetos of anti clockwise rotation driven from the single magneto
gear incorporated in the engine itself, thence by menas of splined driver
connected to this gear thought an impulse coupling which throws both 
magneto armatures by delivering torque to a center helical drive gear
which transfers this torque to both magnetos which are placed 180 * apart
on center line in a horizontal position with their respective drive
gears in mesh with the driver center gear mentioned.

    The left magneto facing the rear of the engine fires the upper
left spark plug and the lower right spark plug, and the right magneto
fires the lower left spark plug and the upper right spart plug,
distribution being made by a collector ring built in each magneto. Since
lubrication is required for the gearing and bearing mountings within
the gear case and bracket assembly of the magneto unit, this is induced
through the rear plain bearing of the center main magneto gear drive
spindle, after which the surplus oil is drained thought an overflow
tube in the magneto drive gear case and back to the engine sump.

    This system eliminates manual lubrication of the entire drive
unit and oil is kep out of the magnetos by a vacuum formed through the
drain line, the original source of the vacuum being furnished by the
breather design of the engine itself.

    With the magnetos removed, the impulse coupling must first be
timed disregarding the magnetos and the coupling must be set to
disengage no later than 5° B.T.C. nor earlier than 5° B.T.C. preferably
the latter.

    Since the main magneto drive gear in the engine has 40 teeth in
its circumference and 6 spline members on the driving member, a selective
timing mechanism is established and by placing the gear in different
positions an accuracy of 1/7 of a gear tooth may be obtained which is
sufficiently close for the impulse setting.

     It must be remembered that when this gear is withdrawn for timing
that the camshaft drive gear must not move in relation to the crankshaft
drive gear or the engine will be thown completely out of valve timing.

    After the impulse is in time within the tolerance previously noted
the magneto gear case and bracket assembly may be bolted in place

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                               PART II

with the two flat head cap screws and the long 1/4" through bolt.
Alingment of the impulse coupling with the drive member must be given
attention so that no bind occurs in the coupling even if a very thin
shim is reuired between the magneto case and bracket and the bracket
on the engine gear cover.

Note should also be made that the center line of the coupling
lines directly with the center line of the driver member in all planes
with the left hand cylinder which is considered to cylinder ito the
left facing the accessory end or rear of the engine set 35° B.T.C. on
the power stroke with the impulse coupling tripped, the left hand
magneto should be slipped temporarily in place with the fibre rubber
block of the breaker arm straight down.  This position will give an
approximate setting and with the breaker housing set in full advanced
postion, the points should be made to break at the desired 35° B.T.C
This may be accomplished by the trail method of removing the magneto
and replacing it agian in the housing each time trying a different gear
tooth position until the closest setting to the desired 35° is obtained.

The helical type gear is incorporated for drive in order to obtain
a veriner adjustment by slipping the magneto in or out.  By means
of this feature a very accurate adjustment can be made.  The wire leading
from the top terminal of this magneto must lead to the top plug on the
left cylinder and the lower wirte should lead to the lower plug on the
right cylinder.  With the engine set in the same position the right
magneto may be temporarily adjusted to fire at the same 35° B.T.C. setting,
however, the fibre rubber block on the contact are on the right magneto
should point straight up and the same procedure for the setting of the 
correct timing should be carried out using methods explained for the
left magneto.

The wire leading from the top terminal of the magneto must lead
too the top plug on the right hand cylinder and the lower terminal should
lead to the lower plug on the left hand cylinder.

he diamond shaped adjustment plate should be placed in position at
the rear of the mounting bracket and the dog point set screws adjusted
just against the magneto bases to insure the correct location of the
magneto longitudinal.  The adjustment screw should then be safetied with
safety wire and the cap screws and plate may be removed.

After both correct positions of the magnetos are obtained their
armature positions should be marked and the magnetos withdrawn from
the housing for the placement of the variable thickness cork gaskets
at their drive end.  This distance should be noted before removal and
gaskets applied approximately 1/32" thicker than the measured space
so that a tight seal is obtained when finally assembled.

                                                       Page 3

                           PART II

The magnetos may now be installed as marked and the diamond shaped
adjustment plate bolted in poiion whch should locate the magnetos as
originally set and the clamp strap may be drawn up slightly.

The syncronizing bar should be placed on the breaker arm housing
levers so that full advance and retired positions can be obtained
and this adjustment can be made by the shifting of the adjustable
clamp type mounting of the levers.

A final check should be made for accurate syncronizing of the points
using a piece of cellophane paper between the points and if necessary
the adjustment screws in the adjustment plate can be slightly moved
to compensate for the possible error of previous settings.

The entire unit may now be tightened and safetied and the ground
caps installed with their respective wires attached to the switch.
A spring supplied is attached to the arms to pull the breaker assemblies
to full advanced postion and is regulated by the sector on the carburetor
spark control rod.

SPECIAL NOTE:

The magnetos have an oil drain hold drilled in the side wall of the
frame directly behind the drive end and the magnetos must be installed
with this hold downward when in their respective horizontal position,
thus, designating the left and right magnetos so that their polarity
repels the north pole of the left magneto facing the north pole of the
right magneto.

Breaker gap settings should be .015 of an inch.

 
                                 AEORNCA AIRCRAFT CORPORATION

                                 MIDDLETOWN, OHIO