Like low tension magnetos, the true high tension type may be of either the inductor or shuttle wound class. All high tension magnetos are positively connected or geared to the engine in such a manner that there is a fixed relation between time of the current impulse produced by the magneto and the firing position of the engine piston.
The current is generated on the same principle as in the low tension shuttle type; that is, by a coil of wire revolving in the magnetic field established by permanent magnets.
During each revolution of the armature, two sparks are produced at an angle of 180° from each other.
The advance and retard of the spark is obtained by means of the timing lever which shifts the timer housing back and forth which results in the primary current being interrupted earlier or later in the revolution of the armature.
Fig. 107. Longitudinal Section Through Bosch High Tension Magneto.
The timing lever can turn through an angle of 40° measured on the armature spindle, and the angle of advance for multiple engines is as follows:
| Advance for 1 cylinder | 40° |
| Advance for 2 cylinders | 40° |
| Advance for 3 cylinders | 50° |
| Advance for 4 cylinders | 40° |
| Advance for 6 cylinders | 27° |
A timer is used with the magneto on a “jump spark” system in the same way as with a battery, providing a vibrating coil is used.
In one type of magneto the Connecticut, the coil is part of the magneto, and is fastened to the magneto frame. This type of magneto uses a non-vibrating coil, and produces but a single spark each time the primary circuit is broken by the magneto timer. As the timer on this type is driven by the magneto shaft, it is evident that the magneto must be “timed” with the engine, or must have its armature shaft connected to the shaft of the engine in such a manner that the timer contact is broken, and the single spark produced at the instant that ignition is required in the cylinder.