G3408 and G3412 Engines Caterpillar

Ignition System

Usage:

Magneto

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Illustration 1	g00579844
Cutaway View Of A Fairbanks Morse Solid State Magneto (1) Alternator. (2) Distributor rotor. (3) Capacitor. (4) Coil. (5) Rotor.

Ignition power is created in the alternator (1). This alternator consists of a rotor that has eight poles. The alternator also has a stator. The stator has four poles. The alternator has a three-phase full-wave rectified output. This output flows into the main storage capacitor (3). A zener diode is located in the end cap. A capacitor and the zener diode regulate the voltage of the capacitor.

The rotor for the trigger (5) is timed to the rotor for the distributor (2). The rotor for the distributor is timed to the engine. The rotation of the rotor for the trigger (5) in the coil (4) will create two properly timed pulses. These pulses are in two coils. The two coils are connected in series. The coils energize the ignition circuit. This is done by discharging a capacitor. This capacitor is discharged through a silicon controlled rectifier SCR switch.

The voltage that is generated by the alternator will combine with the voltage that is generated by the coil. This voltage will flow into one circuit. This circuit will ignite all of the cylinders. Distribution of the voltage to the proper cylinder is accomplished by the rotation of the distributor rotor. This distributor rotor operates as a transformer. The distributor rotor does not perform ignition timing. The distributor rotor will select a cylinder. This cylinder should receive the signal for engine ignition. The distributor rotor and the shaft rotate at engine speed. The distributor rotor and the shaft are positioned for the transfer of energy. This energy is transferred from one coil that surrounds the distributor. The correct SCR switch will ignite the correct cylinder spark plug.

Magneto

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Illustration 2	g00587625
Altronic Magneto (1) Alternator. (2) Electronic firing section.

The Altronic magneto is made of a permanent magnet alternator section (1) and electronic firing section (2). There are no brushes or distributor contacts.

The engine turns the drive tang for the magneto (7). The drive tang turns alternator (3), speed reduction gears (5) and rotating timer arm (9). The power from the alternator will charge the storage capacitor (8). There are separate pickup coils (6) for each cylinder. There are separate silicon controlled rectifiers SCR (10) for each cylinder. The timer arm passes over pickup coils (6) in sequence. The pickup coils turn on the solid state switches (10). This will release the energy that is stored in capacitor (8). This energy leaves the magneto through the wiring harness. The energy then flows to the ignition coils and the energy is transformed to high voltage. This high voltage is needed to fire the spark plugs.

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Illustration 3	g00579848
Cross section of the Altronic solid state magneto (3) Alternator. (4) Vent. (5) Speed reduction gears. (6) Pickup coil. (7) Drive tang. (8) Storage capacitor. (9) Rotating timer arm. (10) SCR solid state switch. (11) Output connector.

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Illustration 4	g00647487
(12) Sensor. (13) Air Gap.

The Caterpillar digital ignition system is designed to operate from a power source that has a voltage of 12 VDC. This system can also operate from a power source that has a voltage of 24 VDC. The controller steps up the voltage. This voltage charges a capacitor in order to store energy. The controller contains a logic microprocessor. The controller contains a relay switch for the storage capacitor. This relay switch will release energy that is stored. This stored energy will be released to the ignition coils. There is a switch that is located on the exterior of the controller. This switch is set for the engine that is being operated. The timing is adjusted for the fuel that is being consumed by the engine. The Magnetic Timing Disc is mounted on a gear that is directly driven by the camshaft gear. This gear is rotating at half of the engine speed. As a magnet passes by the timing sensor, a signal is sent to the controller. This signal tells the controller to fire the storage capacitor. The storage capacitor will energize that coil. The number of magnets in the magnetic disc is equal to the number of cylinders in the engine plus one. The extra magnet follows behind the magnet that was the last magnet to fire. This action is a signal to the CDIS controller. This signal indicates that the next revolution will begin.

Spark Plug Adapter

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Illustration 5	g00608996
(1) Adapter. (2) Seal. (3) Cylinder head. (4) Gasket.

The spark plug adapter (1) is mounted in the cylinder head (3). Seal (2) stops any type of leakage between the adapter and the cylinder head. The adapter extends upward through a hole in the valve cover.

The gasket (4) stops water from entering the combustion chamber. This gasket also prevents combustion gas from entering the jacket water.

Spark Plug And Transformer

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Illustration 6	g00579891
Altronic spark plug and transformer (1) Transformer. (2) Wire assembly. (3) Rubber boot. (4) Seal. (5) Spark plug.

When the Altronic magneto is used, the transformer (1) is mounted on the valve cover. The wire assembly (2) is the lead for high tension. This will ignite the spark plug (5). The rubber boot (3) is part of the wire assembly (2). The boot forms a cover over the adapter and the valve cover. This cover will prevent dirt, water and other foreign materials from entering the adapter. The seal (4) will not allow the vapors from the crankcase to exit the adapter. This seal will also prevent oil from entering the adapter.

Note: The wire assembly (2) and the seal (4) must be installed on all of the cylinders when the engine is running. If these seals are not installed, a spark from the exposed wire assembly may ignite the vapors from the crankcase. This may result in damage to the engine.

Ignition Transformer

The ignition transformer causes an increase of the magneto voltage. This is needed to send a signal across the electrodes of the spark plugs. For proper operation, the terminals must be clean and tight. The negative transformer terminals have a "-" mark. These terminals are connected together. The terminals are also connected to ground. The wiring diagrams show the connection of all of the wires. The wires should be connected to the connection for the plug at the magneto. The wires may be connected at the controller for the CDIS.