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Consult the appropriate Manufacturers Maintenance Publication

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Warning

In the above figure, all switches and relays are in the normal "OFF" position. These diagrams illustrate the electrical operations of the magneto circuits . 

They are not to be used for installation purposes.

 

Starting Vibrator with Relay and Delay

 

With the combination ignition and starter switch in its "START" position, starter soleniod L3 and coil L1 are energized, closing their relay contacts R1, R2, R3 and R4. Capacitor C2 is charged. Relay contact R3 connects the right magneto to ground, rendering it inoperative during the starting procedures. Battery current flows through relay R1, vibrator points V1, coil L2, through retard contact assembly  of left magneto to ground, as well as through relay contact R2 and through the left magneto contact assembly to ground. A magnetic field around coil L2 produced from this currnet causes Vibrator points V1 to open. Current stops flowing through coil L2 causing the magnetic field to collapse and vibrator points V1 to re-close. This allows coil L2 to be energized and vibrator points V1 again to open. This interrupted battery current will be carried to ground through the main and retard contact assemblies.

 

When the engine reahes is normal advance firing position, the main breaker assembly of the left magneto opens. However, vibrator current is still carried to ground through the retard contact assembly, which does not open until starting retard position of the engine is reached. When the retard contact assembly opens(main contact assembly is still open), vibrator current flows through the primary of transformer T1 (magneto coil) producing  a magnetic field around the coil. As the vibrator points V1 open, current flow through the primary of transfomer T1 ceases. This induces a high voltage in the secondary which fires the spark plug. a shower of sparks is therefore produced at the spark plug due to this opening andf closing of the vibrator points V1 while the main and retard contact assemblies are open.

 

When the engine fires and begins to increase speed,  the starter switch is released and the starter soleniod L3 is De-energized. Capacitor C2 discharges through coil L1 (its path through L3 is blocked by diode D1), holding in the relay for a fraction of a second. When capacitor C2 is dicharged, L1 is de-energized. This opens the vibrator and retard contact assembly circuits, rendering them inoperative. The right magneto is no longer grounded and thus both magnetos are simultaneously firing in full advance.

Test, Repair, Inspect and Overhaul Bendix and Slick aircraft magnetos