866456A01 Mercruiser GIMBAL RING ASSEMBLY

General Information
G342 ENGINE ARRANGEMENT
1. Air cleaner. 2. Aftercooler. 3. Instrument panel. 4. Water pump. 5. Governor. 6. Oil filter. 7. Magneto. 8. Auxiliary water pump. 9. Radiator. 10. Ignition transformer (six). 11. Carburetor. 12. Oil cooler. 13. Power take-off clutch.The G342 is a inline 6 cylinder engine. The engine has a 5.75 in. (146 mm) bore and a 8 in. (203 mm) stroke.The engine has a displacement of 1246 cu. in. (20.4 liter). The firing order is 1, 5, 3, 6, 2, 4. The engine weight is approximately 5,250 lbs. (2381 kg).Ignition System
The ignition system has five basic components: A magneto, ignition transformers for each cylinder, a wiring harness, spark plugs and an instrument panel.Spark Gap Magneto
The magneto is an alternating current generator that produces the electric source (and stops it at the right time) necessary for spark ignition engines. The basic components of the spark gap magneto are the transformer, rotor, contact breaker, distributor, and condenser.
CROSS SECTION OF SPARK GAP MAGNETO
1. Distributor disc. 2. Cam. 3. Distributor gear and shaft assembly. 4. Brush and spring assembly. 5. Transformer. 6. Distributor block. 7. Contact points. 8. Condenser. 9. Rotor. 10. Impulse coupling.Transformer (5) has a primary coil made of heavy wire. One end of the primary coil is connected to ground on the transformer core. The other end of the primary coil is connected to contact points (7).Rotor (9) is a permanent magnet. When the rotor turns, one pole of the magnet in the rotor moves under the core of transformer (5). A flow having the characteristics of the magnet (flux) moves from this pole of the magnet to the opposite pole of the magnet through the layers of the metal core. There is an increase in the flux in the core until the pole is exactly under the core. The flux is then at its largest strength. As the rotor turns more it moves out from under the core and there is a decrease in the flux. The rotor turns so that the opposite pole is under the transformer core. Now the flux must change its direction of flow through the transformer coil. The flux gets larger and then smaller in the opposite direction. The flux direction changes each time the rotor makes a revolution. This flux in the core is all around the wires in the coil of the transformer and causes electricity in the wires.Cam (2) opens contact points (7) at the point in the alternating current cycle when the voltage in the primary coil is large.When the points open the circuit is broken and the flux around the primary coil wires suddenly falls (collapses) through the primary coil. This sudden collapse of flux causes the largest voltage (peak voltage) in the primary coil.At peak voltage the contact on distributor disc (1) is in a position to make a complete circuit through brush and spring assembly (4) in the distributor block and through the low tension leads to the ignition transformers.Condenser (8) prevents a spark that can cause damage to contact points (7). The electrical energy which normally makes a spark across the gap in the contact points goes into the condenser. When the contact points open wider, the electrical energy in the condenser moves back into the primary coil and adds to the voltage.When there is an increase of rpm of the rotor, there is an increase in strength of spark at the spark plug electrodes. An impulse coupling (10) is used to cause an increase in rotor rpm as the engine is started. The impulse coupling is not engaged when the engine is in operation.Solid State Magneto (Fairbanks Morse)
The solid state type magneto makes (generates) current in the alternator section of the magneto. Low tension current is held in the capacitor and then released. Distribution is then made through the distribution board (4). This system has no contact points, contactors, or brushes. There is no spark inside the magneto and only minimum wear. An ignition spark of high tension is made by the transformer to start the air fuel mixture burning under all operating conditions.The alternator makes a voltage as the magnet rotor is turned by the engine through a drive coupling. The alternating current is sent through a rectifier and held in a capacitor (5). A zener diode, on the power board is the regulator of the capacitor voltage for proper ignition.As the pulser rotor (8) moves by each pulser coil (trigger circuit) (7), a voltage is made and sent to the electronic switch (silicon controlled rectifier) (9) for the cylinder ready for ignition. The switch is then turned on and permits the capacitor (5) to release the voltage (discharge). Then the voltage goes through the distribution board (4) and to the transformer. The transformer causes a spark (impulse) of high voltage and low current. This is sent across the electrodes of the spark plug. As the pulser rotor moves by each pulser coil, the same development of spark (impulse) is made.
CUTAWAY VIEW OF SOLID STATE MAGNETO (FAIRBANKS MORSE) (Typical Illustration)
1. Timing bolt. 2. Pulser coil assembly. 3. Plate and power board assembly. 4. Distribution board. 5. Capacitor. 6. Alternator housing. 7. Pulser coil (trigger circuit). 8. Pulser rotor. 9. Electronic switch (silicon controlled rectifier). 10. Plug connector.Solid State Magneto (Altronic)
SOLID STATE MAGNETO (ALTRONIC)
1. Alternator section. 2. Electronic firing section.The Altronic magneto is made of a permanent magneto alternator section (1) and brakerless electronic firing circuit (2). There are no brushes or distributor contacts.
CROSS SECTION OF SOLID STATE MAGNETO (ALTRONIC)
3. Alternator. 4. Vent. 5. Speed reduction gears. 6. Pick-up coil. 7. Drive tang. 8. Energy storage capacitor. 9. Rotating timer arm. 10. SCR solid state switch. 11. Output connector.The engine turns magneto drive tang (7). The drive tang turns alternator (3), speed reduction gears (5) and rotating timer arm (9). As the alternator is turned it provides power to charge energy storage capacitor (8). There are separate pick-up coils (6) and SCR (silicon controlled rectifier) solid state switches (10) for each engine