The automobile owner's guide

by Frank B. Scholl

The armature should then be rotated by means of the exposed distributor gear in the direction in which it is driven until the platinum contact points are about to separate, which occurs when the interruptor lever begins to bear against one of the steel segments of the interruptor housing. Timing or installation is completed by replacing the interruptor housing cover and distributor plate, and connecting the cables between the magneto and the spark plugs.

Exact Magneto Timing.—The foregoing will establish the desired relationship between the magneto armature shaft and the engine crank shaft. It should be noted, however, that while these instructions cover the average engine, the exact magneto timing for individual engines is best determined by trial.

When specific instructions for magneto timing are given by the engine manufacturer, it is recommended that such instructions be followed in preference to those herein given.

It must always be borne in mind that while making connections the distributor brush travels in the opposite direction to the rotation of the armature shaft.

The Condenser.—The condenser consists of a set of metal discs, insulated from one another with tin foil. It is carried at the interruptor end of the magneto. It is connected in the primary current and forms a shunt connection with the interruptor contact points, and through resistance to the returning ground current prevents excessive sparking at the interruptor contact points which would soon burn the points and ruin the coils.

The Safety Spark Cap.—A safety spark cap is provided to protect the armature and other current carrying parts. Under normal conditions the current will follow its path to the spark plug, but if for any reason the resistance in the secondary wire is increased to a high point, as when a cable becomes disconnected, or a spark gap too wide, the high tension current will discharge across the safety spark gap.

Caution.—The current should never be allowed to pass over the safety spark gap for any length of time, and if the engine is operated on a second or auxiliary ignition system, the magneto must be grounded in order to prevent the production of high tension current. The snapping sound by which the passage of current across the safety spark gap may be noted should always lead to an immediate search for the cause of the difficulty.

The Safety Spark Gap.—The safety spark gap consists of a pointed metal electrode projecting from the mounting flange of the slip ring holder, inside the shaft end hood. The tip of the electrode extends to within a short distance of the connecting bar, extending from the brush holder to a magneto distributor plate center post.

Timing Range.—The magneto interruptor housing is arranged so that it may be rotated through an angle of thirty-four to thirty-seven degrees with respect to the armature shaft. The movement of this housing in one direction or another causes the interruptor lever to strike the steel segments earlier or later in the revolution of the armature, the spark occurring correspondingly earlier or later in the cylinder. The spark can be advanced by means of moving the interruptor housing which is connected to the spark lever on the steering gear, in the direction opposite the rotation of the armature. The armature rotation is usually indicated by an arrow on the cover at the driving end of the magneto.

Cutting Out Ignition.—Since a high tension current is generated only on the interruption of the primary circuit, it is evident that in order to cut out the ignition, it is merely necessary to divert the primary current to a path that is not affected by the action of the magneto interruptor. This is accomplished as follows: An insulated grounding terminal is provided on the cover of the magneto interruptor housing with its inner end consisting of a spring with carbon contact pressing against the head of an interruptor fastening screw. The outer end of the grounding screw is connected by low tension cable to one side of the switch, and the other side of the switch is grounded by connecting a cable between it and the engine or frame. When the switch is open the primary current follows its normal path across the interruptor points, and is interrupted at each separation of these contact points. However, when the switch is closed, the primary current passes from the head of the interruptor fastening screw to the carbon contacts of the grounding terminal, thence through the switch to the engine and back to the magneto, and as the primary current remains uninterrupted when following this path, no ignition current is produced.