Dual Magnetos - Twin Plugs

Dual magnetos for use with twin plugs are similar to those used with single plugs in that HT is generated by both magneto and battery/coil sections. Both types of dual magneto use the same duplicated system of CB points, described on the Dual Magnetos - Single Plugs page. The twin plug versions of the dual magneto described on this page have a different rotor/distributor system.
The dual magneto - twin plug units have two distributors, one for each set of spark plugs. The magneto HT path comes from the magneto pickup and under the magnet itself to the rotor arm. The battery/coil HT path comes into the rotor arm from the opposite end via a connection on the front of the distributor cap -  very similar to the single plugs version of the dual magneto. 

The following picture shows a Bosch D4  dual magneto - twin plugs. The parts of interest are numbered as follows:

  1: rear distributor used by the magneto section feeding one plug per cylinder

  2: front distributor used by the battery/coil section feeding the second plug per cylinder 

  3: Connection point for the HT from the independent HT coil used by the battery/coil section

  4: Magneto cut out terminal

  5: Connection to CB points used by the battery/coil section - a low tension wire goes to the HT coil

The big difference is in the design of the rotor arm. This is a one piece unit but with two independent paths taking each of the two HT sources just described via two carbon brushes to the two distributors. 

As with the Dual Magneto - Single Plugs versions, these dual plug versions use the same combined HT coil and changeover switch together with a battery to complete the system.