(Not for the Purist and only if you’ve got 12V electric)

Introduction

This document describes an electronic ignition for Indians. The trigger unit fits into a standard Autolite distributor and does not interfere with the manual advance and retard control used on Indians.

For reliability reasons most of the components are commercially available electronic ignition components from an ignition system produced by Bosch in the 70s and 80s and used in many European cars (Volkswagen, Ford) and motorbikes (BMW).  Therefore, most of the parts required can be found at a breakers yard. Using those commercial products however requires that we have a 12V electric on our Indian, which I achieved by using a 170W 12V Bosch generator from a beetle that has exactly the same dimensions than the original Autolite 6V generator.  As the components are readily available there is no electronic skill required in wiring it up. However, the production of the actuator requires some mechanical skills and the use of a lathe.

Working Principle

The ignition uses a “Hall Sensor” instead of mechanical contact breakers. This hall sensor is an electronic device that detects the presence of a metal vane passing through the gap between a magnet and the sensor. It not being an optical or mechanical sensor makes it extremely robust against dirt, moisture and oil. The electric signal from the hall sensor is delivered to the “Ignition Control Unit”. This control unit switches the current to the ignition coil. The switching is done much faster than with a mechanical breaker. Therefore, the ignition coil produces extremely high voltages, independent on the engine speed.

Parts Required

Most of the parts are available from a good breakers yard, and can be salvaged out of an old hall sensor distributor. Where known I give component numbers from possible suppliers.  Some of the parts are available from electronic components suppliers. As I’ve used RS and they have an almost world wide coverage, I will give the RS order number (where available)

1 Ignition Trigger Unit  -  Bosch 0227 100 123, Siemens 5WK6 101

Volkswagen 211 905 351E

1 Hall Sensor  - Salvage or RS 178-5689

1 Ignition Coil* WC 0221 600 016 (yellow label)

1 1Ω 100W Resistor** RS 188 087

Some cable

Some crimp connectors

1 Actuator - Home made

*Bosch distinguishes the different ignition coils by the color of the label. The ignition coil that is suitable for the hall sensor ignition MUST have a yellow label. Ignition coils with blue (breaker point ignition) and green (more modern electronic ignition) will destroy the ignition trigger unit.

**In the car, where the ignition comes from this resistor it is not obviously present. It consists normally of a resistance cable as part of the wiring loom. (I have tried a cheaper 50W version of this resistor and fried it!)

The Actuator and Distributor Modifications

The actuator looks like the end of a tin cup and should be made from low carbon steel (better in conducting the magnetic field). The top should be formed in a way that the original distributor finger can be installed into the distributor case. Diameter of the actuator should be 40 mm. 

The sides of the actuator are two approximately 10-mm long and 25 mm wide vanes with the resulting gaps. Rotation of the actuator is clockwise with half the engine revs.  The ignition coil receives current whilst the metal vane is passing through the magnetic field of the hall sensor. And is switched off (ignition point) when the vane leaves the sensor. 

To achieve the correct ignition points for both cylinders on our 42° V-twin the ignition  point for the front cylinder has to be 201° after the ignition of the rear cylinder ( 180° for the opposing working cycle plus half of the 42° difference to compensate for the V of the cylinders. On a parallel twin or boxer the ignition would be evenly spaced at 180°)

A schematic of the actuator principle can be seen in Figure 1 (wiring diagram and actuator details). My actual actuator unit is shown in Figure 4 (The actuator) and Figure 3 (The complete assembly with the part removed actuator).

The notch for the distributor finger must ensure that the finger is pointing towards the corresponding pick up on the distributor cap, when the vane passes through the ignition point (see Timing of the Ignition)

The hall sensor is fitted into the distributor body so that the vanes of the actuator pass through the gap of the magnetic field without touching the sensor body. The cables are lead through to a three feed of a similar make to the one already there for the breaker connection. The installed hall sensor can be seen in Figure 2 (Position of hall sensor).

Wiring it up

The wiring should be done in good quality automotive cables. The cables between the hall sensor and the ignition control unit have to carry almost no current (TTL signal) and therefore can be rather thin. The sensor cable will probably run parallel to the ignition cable and therefore should be screened. The screen should be connected to ground.

The power supply cable to the ignition control unit and to the ignition coil should be at least 0.75 mm2, I would use 1.5 mm2. 

The ignition control unit dissipates quite some heat. To prevent it from overheating it should be installed on a large piece of metal (e.g. inside the toolbox or between the tank). Before fitting it, one should apply heat conductive paste between the unit and the metal.

The ignition coil for the hall sensor ignition operates at only 9 Volts. Therefore, the 1Ω resistor has to be fitted in line. Not doing so will result in the death of the ignition trigger unit and or the ignition coil. This 1Ω resistor is normally a resistance cable, but for ease of use is in this case replaced with a 100W metal case resistor.

For easy assembly I fitted two more “feed through” on the distributor case, similar to the one already used by the breaker points. Onto these, I connect the signal cable using crimp rings. The connector on the ignition control unit uses 3.5 mm flat crimp connectors, the ignition coil uses 6mm crimps. To toughen the connections I have used heat shrink tube around the shaft of all crimp connectors.

Timing of the Ignition

The timing point is when the vane of the actuator is passing a point that is 1 mm behind the center of the hall sensor (in rotation direction). The rest of the timing is done as with a contact breaker ignition.

WARNING

An electronic ignition produces extremely high voltages of approximately 30 000 Volts (mechanical ignition 15-20000Volt). Those voltages can be lethal. Therefore, considerable care has to be taken when working on electronic ignition components.  Never touch any bare wires on the high voltage side of the ignition without ensuring that the battery is disconnected and the wire has been grounded. Ensure that you use high quality and in perfect condition ignition leads and safe spark plug caps.

Disclaimer: Every one wanting to re produce the electronic ignition described here does so entirely on his/her own responsibility. I accept no responsibility on injury caused or for the correctness of the given information.

Figures

Frank Nuber