1917 Cadillac - GM Heritage Center

22 OPERATION AND GENERAL CARE
AUTOMATIC SPARK CONTROL
When each piston is at its highest position in the cylinder is, of course,
the time when the charge is at its greatest compression, or, in other words,
when the gas is "jammed in the tightest." Ignition occurring exactly at this
instant produces a much more forceful explosion than if it occurred at a time
when the charge was not so tightly compressed.
If the charge were ignited the instant the contact is made in the ignition
timer, regardless of the speed of the engine, the spark could be set permanently
in one position and would not require changing. But a certain
amount of time elapses from the instant the circuit is closed at the ignition
timer until the charge is ignited in the cylinder. While this time is but the
merest fraction of a second, in fact, almost infinitesimal, yet it is time just the
same and must be taken into account when dealing with such a rapidly acting
mechanism as an automobile engine.
The lapse of time required to ignite the charge is always the same regardless
of the speed of the engine and pistons. You will realize that when the
engine is running say 3000 R. P. M., the pistons are traveling many times
as fast as they do when it is running only 300 R. P. M. and that when the
engine is running 3000 R. P. M. it is necessary to start the ignition process
earlier.
In the Cadillac this is accomplished by means of a ring governor located
directly under the ignition timer. (See Fig. 33.) As the speed of the engine
increases the ring in the governor assumes a position more nearly horizontal,
forcing the timer contact cam slightly ahead on the shaft by which it is
driven. This causes the timer contact points to break earlier, thereby
starting the ignition process earlier in relation to the positions of the piston.
When the engine slows down, the ring in the governor assumes a position
more nearly vertical, forcing the contact cam back on the shaft by which it
is driven, causing the contact points to break later and thereby starting the
ignition process later in the stroke of the pistons.
MANUAL SPARK CONTROL
The automatic control takes care of the_ spark position for all ordinary
driving. A spark lever is provided, however, by which the ignition timing
may be still further advanced or retarded. The spark lever is the shorter
lever just above the steering wheel.
Ordinarily the spark lever should be carried in that portion of the sector
marked "Driving Range." To get the best results, however, the spark lever
should be retarded further for extremely low speeds and advanced further for
extremely high speeds. The car should be driven at all times with the greatest
possible spark advance which the speed of the engine will permit.
Advancing the spark too far for a given engine speed will usually cause a
slight pounding noise, which is sometimes not noticed by the beginner as it
is usually but slight owing to the substantial character of the crankshaft and
bearings.
When starting the engine, place the spark lever in the "Driving Range"
on the sector except during extremely cold weather when it should be placed
at the extreme right or in the fully advanced position. If the engine should
be cranked by hand, the spark lever should be placed at the extreme left on
the sector or in the fully retarded position. If this caution is not observed a
"back kick" may occur, probably resulting in injury to the person cranking.
OPERATION AND GENERAL CARE 23
TO COAST
To coast on the level, close the throttle and" then release the main engine
clutch by pushing forward on the left pedal.
When descending grades a good method is to close the throttle, switch
off the ignition and allow the engine to do the holding back as much as
possible. This saves much wear on the brake band lining.
When descending steep grades, the resistance offered by allowing the
car to drive the engine when "high gear" or "direct drive" is engaged is
usually sufficient to control the speed. When the engine does not offer
sufficient resistance the speed may be further checked by applying the foot
brake.
When it is necessary to descend a very steep grade it is best to engage
the intermediate or possibly the low speed gears before commencing the descent,
and if the resistance of the engine thus obtained is not sufficient, supplement
it by the foot brake. Bear in mind that the more the resistance of
the engine is used in coasting the longer the brake band linings will wear
and the brakes retain their adjustment.
The principle of this method will be understood when you realize that
the same combination of gearing which changes the ratio between the engine
shaft and the rear axle, which makes it easier for the engine to drive the car,
will, when the car is compelled to drive the engine, have exactly the opposite
effect, which is the case when the above method is used in descending a hill.
RULES OF THE ROAD
Road and traffic laws vary greatly in different localities. It is, therefore,
impossible to set down a complete list of rules which may be followed in all
parts of the country. The following are some of the rules which are practically
universal in all parts of the United States.
In meeting a vehicle going in the opposite direction pass to the right.
In passing a vehicle going in the same direction pass to the left.
Always stop with the right hand side of the car next to the curb. If it is
necessary to turn around to do this it should be done.
Never turn around or turn off onto another road without making absolutely
sure that there is no other vehicle directly behind you.
Never enter upon street car tracks without making sure that there is no
car directly behind you—no matter how sure you feel, look and see.
Do not cross street car or steam railroad tracks without making sure
that it is absolutely safe to do so.
In crowded traffic do not apply the brakes suddenly unless it is absolutely
necessary. It may be that the vehicle following you cannot stop as quickly
as you can. If this is the case a collision is sure to result.
On wet asphalt streets or slippery roads do not apply the brakes suddenly
unless it is absolutely necessary. If the brakes are appl'ed suddenly under
these conditions disastrous skidding is apt to occur.
In crowded traffic it is a good plan to signal cars at the rear, before
turning, slowing down or stopping.
It is a good plan to slow down in passing vehicles going in the opposite
direction.
One of the most essential things to remember is that you should never
"take a chance." You will find that the more experienced drivers never permit
themselves to take a chance.