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IGNITION
IGNITION OPERATION
(PRE-1985 Production)
MAGNETO IGNITION.
Tecumsehs magneto ignition
consists of a stator assembly made up of a coil,
laminations, contact points, condenser, and a permanent
magnet mounted in the flywheel of the engine.
COIL:
The coil consists of a primary and a secondary
winding of wire. The primary is the low voltage (200-
300 volts) primary winding consists of about 150 turns
of heavy gage wire next to the core. One end of the
primary is connected to the insulated contact point
and the other end is grounded to the stator body.
The secondary winding consists of extremely fine wire
with many turns (about 10,000) wrapped over the primary
windings. One end connects to the spark plug and
the other end is grounded to the stator body.
The coil is used as a transformer to increase the primary
voltage to a high voltage (10,000 - 20,000 volts) which
jumps across the spark plug gap.
*The actual connection of the primary and secondary ground is
normally made inside of *the coil, but it is shown above to illustrate
the individual wires.
CONTACT POINTS.
The contact points consist of an
insulated movable point that connects to the coil primary
lead and a stationary point that is grounded to the
stator body which provides the return path for the
primary circuit.
CONDENSER.
The condenser acts as an electrical
shock absorber to prevent arcing between the contact
points as they open. Arcing lowers the voltage at the
spark plug, as well as burn and pit the contact points,
thus shortening point life.
OPERATION OF THE TECUMSEH MAGNETO
IGNITION.
As the flywheel turns, the magnets (mounted
in the wheel) pass the coil mounted on the stator. As
the magnets North Pole enters the area of the center
leg of the stator, a magnetic field is concentrated through
the laminations to the magnets South Pole. This causes
a generation of current flow in the coils primary winding.
The ignition points are closed.
PRIMARY LEAD
SECONDARY
GROUND LEAD
GROUND LEAD
TERMINAL
FOR PRIMARY
AND SECONDARY
PRIMARY
GROUND
LEAD
PRIMARY
WINDING
SECONDARY
WINDING
SECONDARY
LEAD
FLYWHEEL
ROTATION
MAGNET
POINTS
CLOSED
PATH OF MAGNET
LINES OF FORCE
PRIMARY
WINDING
As the flywheel continues to rotate, the North Pole
approaches the last leg of the lamination stack. The
magnetic field through the center leg reverses, producing
a large change in the magnetic field and a high current
in the primary windings of the coil.
At this time, the contacts open and the primary current
stops flowing. This change in current causes a voltage
in the primary windings, which induces the high voltage
in the secondary winding of the coil. The voltage is
routed through the spark plug wire, to the spark plug,
and then jumps the gap of the plug to ignite the fuel
air mixture.
POINTS OPEN
Summary of Contents for AH520 -
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