american bosch
 BEP vB APA СТАИ AA E DA
UNITED AMERICAN BOSCH CORPORATION, SPRINGFIELD, MASS, U. S. A.
AMERICAN
BOSCH
PRODUCTS
MAGNETO TIMING
Generally speaking, all magnetos are timed so that they will fire the clyinder under
compression at top dead center with the timing arm in the fully retarded position.
While
this method usually is satisfactory, it is nevertheless true that, under certain conditions, the
above procedure w:// not always procure the desired results.
It is, therefore, in order to explain the timing of a magneto in detail and point out
definitely the importance of observing certain items in order that best results may be obtained
under all conditions.
1—Four Cylinder Four Cycle Motor
Magneto driven at crank shaft or engine speed.
A four cylinder four cycle engine produces two ex-
plosions per revolution of the crank shaft and it will
therefore be necessary to run the conventional four
cylinder magneto which delivers two sparks per revolu-
tion of its armature (or one every 180° travel) at engine
spee
The relation between engine travel and magneto
travel is consequently :
360° to 360°
360 1
— ee 0 |
360 1
Since the magneto is driven at engine or crank shaft
speed, it must follow that the angular relation between
the timing movement of the interrupter es and
the angular movement of the crank shaft is the same.
In other words, when the ice flywheel i traveled
35°, the magneto armature has also moved 35°. If
then, this particular magneto has a 35° timing range,
the actual spark can be made to occur anywhere from
top dead center to 35° ahead of top dead center, pro-
vided the e was originally timed top dead center
in full reta
Tirer. if you require more than 35° advance,
you must time the magneto ahead of dead center at full
retard to an amount equivalent to the number of degrees
which you require in addition to the 35° which the
magneto provides.
If you are timing a slow speed, high compression
engine, it might be advisable to set the magneto from
5° to 10° past dead center at full retard, thus sacrificing
fhe number of degrees of the magneto advance obtain-
able.
2—Six Cylinder Four Cycle Motor
with Magneto Running Faster
than Engine Speed
A six cylinder four cycle engine produces three ex-
plosions per revolution of the crank shaft and it will,
therefore, be necessary to run the conventional six cyl-
inder magneto which delivers two sparks per revolution
(or one every 180° travel of the armature) at a speed
to produce three sparks during that period. In other
words, it must travel through 180° +1 180° + 180° or
540° which is equivalent to 154 engine speed.
The relation between engine travel and magneto
travel is consequently:
(360° x 1.5) to 360°
or 540 to 360
540 1.5
or— = — ог 114 tol
360 1
When the magneto is not driven at engine speed, its
timing range, as measured at the engine crank shaft,
is changed accordingly.
Due to the fact that the magneto speed is 174 times
engine speed, it must follow that the angular rela-
tion between the timing movement of the interrupter
housing and the movement of the crank shaft on the
engine, must also be 174 to 1. As an example, when
the magneto has traveled 35°, the engine flywheel has
only traveled 23°. This is explained as follows:
35 350 7
— = — = — = 23° (Disregarding the minutes)
1.5 15 3
Again, then, if this particular magneto has a 35°
timing range, the actual spark can be made to occur
anywhere between top dead center and 23° ahead of
dead center, provided magneto was originally timed top
dead center in full retard. Therefore, if you require
more than the 23° advance, you must time the magneto
ahead of dead center in full retard, to an amount equiv-
alent to the number of degrees which you may require
in addition to the 23°.
3—Two Cylinder Four Cycle Motor
(Firing at Equal Intervals)
Magneto driven at cam shaft or 14 engine speed.
A two cylinder four cycle engine produces one ex-
TAE EIA al TADA ET
UNITED AMERICAN BOSCH CORPORATION, SPRINGFIELD, MASS., U. S. A.
plosion per revolution of the crank shatt, and it will
therefore be necessary to run the conventional two
cylinder magneto which delivers two sparks for each
revolution of its armature (or one every 180° of
travel) at a speed to produce one spark during that
period, or at 14 engine speed.
In other words, it must travel:
°х 14 to 360%
or 180° to 360°
„380 1
— = _orMtol
"360 2
The angular relation between the timing movement
of the interrupter housing and the angular movement
of the crank shaft is therefore the same or 14 to 1. In
other words, when the magneto armature has traveled
= , the engine crank shaft is rotated twice that amount
0°. If, then, this pis Maia has a 35%
“olor range, the actual spar made to occur
anywhere from top desd er ® 70° ahead of top
dead center, provided the magneto was originally timed
top dead center in full retard.
Therefore, if you require less than 70° advance, you
must time the magneto past dead center at full retard
to an amount equivalent to the number of degrees which
vou require. Obviously, the better method is to use a
magneto with a 20° timing range.
Another alternative would be to run the magneto at
crank shaft or engine speed. Due to the fact that the
magneto delivers two sparks ‚per revolution of its arma-
ture where only one spark is required, it must follow
that one spark must alternately be dissipated in the
engine exhaust.
Either procedure is, however, frequently objection-
able. The former on account of hard starting (espe-
cially when no impulse coupling is employed) which is
due to the 14 engine speed at which the magneto is
running —and the latter is often unsuitable due to the
waste spark causing an explosion through the carburetor,
depending on the valve setting of the particular engine.
Therefore another method has been developed which
is known as the 4/2 magneto application.
Such a magneto is a four cylinder instrument driven
at engine or crank shaft speed with either two alternat-
ing terminals of its distributor entirely eliminated or
two adjacent distributor terminals bridged and led to
ground through a safety gap.
The first mentioned magneto uses one cam only in its
interrupter housing, while in the latter one two cams
must be employed. The latter type is used on two cvl-
inder four cycle engines which fire at unequal intervals
similar to that explained in chapter number 4.
A four terminal two pole magneto for use on two
cylinder four cycle engines, == running at crank
shaft speed. Engine is fired eve igh tension
terminals 2 and 4 are omitted ua the meras hous-
ing of this magneto has only one cam to provide only
one spark for every revolution of the armature.
The relation between engine travel and magneto
travel is, therefore:
360° to 360°
1
SEE dal isn)
1
4/2 360° Magneto
4—Two Cylinder Four Cycle Motor
(Firing at Unequal Intervals)
A four terminal two pole magneto for use on two
cylinder four cycle engines on which explosions occur at
unlike intervals, namely 180° and 540°. Therefore
high tension terminals 3 and 4 are connected together,
through the safety gap, to ground and the interrupter
housing of such a magneto must have two cams to
provide two working sparks for every other revolution
of the armature.
The relation between magneto degrees and engine
degrees is consequently:
360° to 360°
“Er
4/2 180° Magneto
UNITED AMERICAN BOSCH CORPORATION, SPRINGFIELD, MASS., U. S. A.
5—Three Cylinder Four Cycle Motor
with Magneto Running Slower
than Engine Speed
A three cylinder four cycle engine produces three ex-
plosions for every two revolutions of the crank shaft.
It will, therefore, be necessary to run the conventional
three terminal magneto which delivers two sparks per
revolution (or one every 180° travel of the armature)
at a speed to produce three sparks during that period
(720° of engine trave n other words, the magneto
must travel 180° + 180° +4 180° or 540° during the
same time that the engine crank shaft travels 720°.
The relation between engine travel and magneto
travel is consequently:
540
.75
— or — or 34 to 1
720 1
When the magneto is not driven at engine speed, its
timing range, as measured at the engine crank shaft, is
changed accordingly.
Since the magneto speed is 34 engine speed, it must
follow that the angular relation between the timing
movement of the interrupter housing and movement of
the crank shaft on the engine, must also be 34 to 1. In
other words, when the engine flywheel has moved 35°,
the armature has actually moved 46°. This is explained
as follows:
35 3500
= — 46° (We have disregarded the
75 75 minutes)
Again, then, if this particular magnets has a 35°
timing range, the actu rk e to occur
anywhere within this range, that is, bot top dead
center and 46% ahead of dead center (provided magneto
was originally timed top dead center in full retard).
Therefore, if you require less than the 46° advance, you
must time the magneto past dead center in full retard
to an amount equivalent to the number of degrees which
you may require less than the 46°.
6—Standard Magneto Timing Instructions
The following instructions are for general purposes
only and apply principally to variable ignition.
FOR MOST EFFICENT OPERATION OF
THE INDIVIDUAL ENGINE, ALWAYS FOL-
LOW THE IGNITION TIMING INSTRUC-
TIONS ISSUED EY THE MANUFACTURER
OF THE ENGINE.
When fixed spark ignition is used, the timing must
be done by the piston in a position 15° to 40° before
top dead center (according to maker's specifications) to
procure maximum efficiency. Correct timing as recom-
mended by the engine manufacturer, is generally nds
ated on the flywheel. ALWAYS FOLLOW EN
GINE MAKER'S INSTRUCTIONS.
General Instructions
Rotate the engine crank shaft until number 1 cylin-
der (in automobile practice this is the cylinder nearest
the radiator) is exactly on top dead center of the com-
pression stroke, and maintain the piston in this position.
Next secure the magneto to the bracket or support pro-
vided for on the engine and place the timing arm of the
interrupter housing in the fully retarded position.
Now remove the distributor plate and the interrupter
housing cover so that the distributor brush as well as
the interrupter contact points may be observed.
The armature should then be rotated by hand in the
direction in which it is to be driven until the platinum
interrupter contacts are just about to separate, which
occurs when the interrupter lever begins to bear against
one of the steel interrupter cams.
Hold the armature in that position while you connect
the magneto drive to the engine and take due care that
the piston of No. 1 cylinder remains exactly on top dead
center. The installation is An by replacing the in-
terrupter housing cover distributor plate and con-
necting the cables Bethke DE magneto and spark plugs.
Obviously, spark plug of 1 cylinder must be con
nected to the distributor jeriinal which is in contact
with the distributor brush and the other wires must be
connected in their proper sequence (depending on the
rotation of the magneto) in accordance with the firing
order of the cylinders.
To time a magneto equipped with an impulse coup-
ling, set No. 1 cylinder on top dead center position of
the compression stroke, and revolve the armature until
the coupling is released from the arrester plate; when
this occurs, rotate the armature backward until the
interrupter lever again crosses the cam and then rotate
it in the proper direction until the points are just begin-
ning to open. After this has been done, proceed in the
same manner as you would with a magneto not equipped
with an impulse coupling.
7—American Bosch Impulse Coupling
Characteristics
When a magneto is equipped with one of our Type
IC-200 or 250 Series Impulse Couplings, it must be
borne in mind that the coupling construction incorpo-
rates three variables which permit any desired degree
The American Bosch Type IC coupling is described
in detail in Section 3150 of the American Bosch Serv-
EST TS A a BEL A NN A ES A
UNITED AMERICAN BOSCH CORPORATION, SPRINGFIELD, MASS., U. S. A
ice Manual, and we recommend that you familiarize
yourself with these details so that you may thoroughly
understand the follo owing.
The three variables are:
1. Le total spring windup controlling the impulse
movement or the movement of the coupling through
the ue “A” indicated on Figure No. 1, which angle
is measured from the point of arrester plate engagement
to the point of arrester plate release (through the cam
action).
2. The angle “B” indicated on Figure No. 1, or the
coupling movement from the time of arrester plate en-
gagement to the edge of the pole shoe.
SI
3. The armature edge distance or the angle “C” indi-
cated on Figure No. 2 whic the angular
through which the armature has traveled away
the edge of the pole shoe before the spark occurs.
Therefore, if the magneto has been timed to the en-
gine so that the impulse spark will occur at top dead
center, the actual spark advance obtained (at an engine
speed at which no impulsing occurs) will be equivalent
to the number of degrees expressed by the angle A—
(B+C
For emi if A = 60°, B= = 5° the
actual spark advance will be us. El 5 or 30°.
It should be noted that, while the coupling is impuls-
ing (at slow engine speed), the magneto timing range
or its interrupter housing movement has practically no
influence on the timing. as an engine speed is
obtained however, which prevents the coupling from
impulsing, the timing range is affected by the movement
of the interrupter housing in identically the same manner
as if no coupling were affixed to the magneto at all.
Obviously it is always advisable to select a Type IC
American Bosch impulse coupling which gives the proper
advance necessary for the particular engine. If, for any
reason, you must reduce the advance of any particular
coupling installed on a magneto (without making a
coupling change), it is necessary to time the magneto by
the running spark (with timing arm in fully advanced
position) as many degrees ahead of top dead center as
may be required and totally disregard the impulse spark.
8—Timing a Magneto Equipped with American
Bosch Impulse Coupling
When a magneto has been equipped with American
Bosch Type IC impulse coupling, two methods may be
followed in timing the instrument to the engine.
1st. By disregarding the coupling ar and timing
the instrument at top dead center of the compression
stroke, as previously explained.
2nd. By timing the magneto so that the impulse
spark occurs at top dead center.
Was this manual useful for you? yes no
Thank you for your participation!

* Your assessment is very important for improving the work of artificial intelligence, which forms the content of this project

Download PDF

advertising