Opel 1900 1973, Service Manual, Page: 40 / 625

IGNITION SYSTEM 19
The ignition key must be
released as soon as engine starts. The switch then
returns
to the on position.
IGNITION
The ignition coil consists of a laminated non- mag-
netic iron
enclosed by two coils; the primary
winding and the secondary winding.
The circuit consists of the power source
(battery), the ignition switch, the ignition coil pri-
mary winding, the distributor breaker points with
ignition condenser connected in parallel, and all con-
necting
tension wiring.
The secondary circuit consists of the ignition coil
secondary ‘winding, the spark plugs, all connecting
high
wiring, the distributor cap and the
t o r .
When the’ ignition switch is turned on and the
breaker pdints are closed, current flows through the
ignition
primary winding and produces a mag-
netic field wound the coil windings.
When the breaker points are separated by the revolv-
ing distributor cam, the magnetic field collapses and
induces a high voltage surge in the secondary wind-
ing,
a spark between the spark plug elec-
trodes. ,
The ignitidn condenser which is connected in paral-
lel with breaker points, prevents arcing between
the breaker contacts, and current flow
the points have been separated, thus
causing a rapid collapse of the magnetic field
around Ignition coil.
IGNITION ‘DISTRIBUTOR
The ignitidn distributor breaks the primary current,
high voltage surges induced in the coil
secondary winding to the spark plugs according to
the
tiring order and sets ignition timing in
relation to. engine RPM and load.
The of the distributor contains the centrifu-
gal advance mechanism and the movable breaker
plate
breaker lever and contact support. The
vacuum advance mechanism is attached to the
breaker
and mounted on the outside of the
distributor, housing. See Figure
The distributor shaft is driven by a helical gear on the
camshaft and in turn drives the engine oil pump. The
ignition condenser is mounted on the outside of the
housing. The engine output is to a large extent in-
fluenced
the ignition timing. Maximum engine
performance is obtained when the combustion proc-
ess is well underway as the piston starts
down on
the
power stroke. The air-fuel charges are, however, not
burned instantly, so it is necessary to advance the
spark in relation to the piston top dead center as
engine speed increases or as engine load decreases.
If the spark is too far advanced, the engine knocks,
causing a drop in engine power output and overheat-
ing. If the spark is retarded, part of the energy deve-
loped during combustion is wasted which will result
in reduced engine power output, excessive fuel con-
sumption and overheating.
The ignition distributor has a double acting double
diaphragm vacuum unit. See Figure
The ad-
vance unit is supplied with “ported” vacuum. That
is, vacuum is supplied from a port in the primary
barrel of the carburetor located just above the closed
throttle valve. This port supplies no vacuum during
idling nor during closed throttle deceleration, but
supplies full intake manifold vacuum at all speeds
where the throttle valve is opened enough to uncover
the port.
Figure Ignition Distributor
The retard unit is supplied with intake manifold
vacuum at all times by means of a line connected
directly to the intake manifold. During idling and
deceleration, when there is no vacuum to the ad-
vance unit, the retard unit will cause the timing to be
retarded 5 degrees. However, during part throttle
operation when there is vacuum to the advance unit,
the advance unit will overpower the retard unit so
that the retard unit has no effect on timing.
The purpose of the retard unit is to reduce hydrocar-
bon and carbon monoxide emissions during idling
and deceleration, where they are especially bad.
In order to avoid voltage losses for easier starting, a
plastic cover has been inserted in the distributor be-
low the rotor as a
to keep the inside of the
distributor cup free from condensation.