Explanations: Ignition and Starting Systems Flashcards
What does a magneto magnetic circuit consists of?
A permanent multi-pole rotating magnet, a soft iron core, and pole shoes.
What determines a magneto’s output?
The speed of the rotor and the strength of the permanent magnet.
What does it mean to hold the points open on a magneto?
To prevent the contact points within the magneto from closing the circuit.
How is the strength of a magneto magnet checked?
The magneto is mounted on a test stand and driven at a specified speed.
The breaker points are held open and the primary current is measured with an AC ammeter.
What is the significance of the E-Gap position?
It is at this point that the flux change is greatest and the primary current is the greatest.
What is the full-register position of a magneto?
In the full register position, the magnet is fully aligned with its pole shoe faces.
What is the internal timing of a magneto?
the timing of the opening of the breaker points relative to the position of the rotating magnet and the distributor rotor.
What happens if the breaker points gap is increased?
The spark will occur early, and because the magneto will be out of time internally, the spark will be weak.
How are high-tension ignition cables “shielded?”
By being routed inside a flexible metallic conduits or braid.
The electromagnetic field radiating from the conductor during the time the spark is occurring at the spark plugs, is picked up by this shielding and carried to ground so it cannot cause radio interference.
Explain the purpose of the safety gap in some magnetos.
Safety gaps are in the secondary circuit of a magneto to protect the insulation of the secondary coils.
If there is an open in the secondary circuit (such as could be caused by a lead being left off a spark plug), the voltage will build up high enough to cause a spark to jump across the safety gap rather than allowing the voltage to rise high enough to damage the secondary coils insulation.
What occurs when the breaker points erode? - when the cam followers wears?
Breaker points erosion causes the timing drifts early.
Cam followers wear causes the timing to drift late.
What causes a magneto to fire?
By cutting off the current flowing to the primary winding, which causes a current to be induced into the secondary winding.
What is a shower of Sparks ignition system?
A shower of Sparks is produced at the spark plug due to the opening and closing of the vibrator points while the main and retard contact assemblies are open.
What is a taper-ground cylinder?
The large mass of the cylinder head expands more when heated than the smaller mass of the cylinder barrel, so the diameter of a choke-ground cylinder becomes uniform when the engine is at its operating temperature.
