The Model T Ford autombiles had a rather unique ignition...the ignition
switch had three positions---"OFF", "BAT" and "MAG". The "OFF" position is
self-explanitory, the "BAT" position connected the ignition system to a more
or less regular, six-volt, liquid type rechargeable battery, and the "MAG"
position hooked the ignition components to a magneto which was built-in to
the engine's flywheel.
Ignition components comprised 4 spark plugs (One for each
cylinder),a gear-driven, (at 1/2 crankshaft speed))"timer" and four
individual spark "coils" mounted in a special box or tray located on the
passenger side of the fire-wall. The timer consisted of an
adjustably-fixed-positioned cup-like cap with four low-voltage wires, each
connected to a short segment of an interal rotary "raceway". A roller
contact, mounted on the timing shaft, completed the primary circuit of each
of the spark coils, for about 10 or 15 degrees of crankshaft rotation,
corresponding to the engine's firing order. (That 10 or 15 degrees is a
SWAG, based on a failing memory.) When an individual coil's primary circuit
was completed electro-magnetically operated make/break contact points
vibrated to provide on-off electric flow in the primary winding, and induce
high voltage current in the secondary winding, connected to the spark plug,
which ignited the fuel in the cylinder.
The timer cap was rotatable, to advance or retard ignition in
relation to the piston's position. It was connected to a lever, positioned
just below the steering wheel, opposite the throttle lever. To eliminate
"kicking" while cranking the engine, the throttle lever was positioned about
half-way wide open, and the spark lever to full retarded position.
Immediately after the engine started the throttle setting was reduced and
the spark advanced. (As an aside, our neighbor, Art Lundgren, had a habit
of holding the spark lever with one hand and the throttle with the other,
usually directly below steering wheel spokes. When Art turned one way he
pulled the throttle open and retarded the spark, if he turned the other way
he closed the throttle and advanced the spark. fortunately Art never
traveled very fast, and I don't remember him ever having an accident)
Those ignition coils were a veritable gold mine for a curious kids
when they were discarded! There was the primary winding of insulated about
18 or 20 gauge wire...probably something like 200 feet of it, gillions of
feet of thin wire secondary winding, and enough tin foil wrapped if
alternate layers of waxed paper (the condensor in the secondary circuit) to
make just about anything a fellow could dream up. And the core for the
windings was a bundle of iron wires, about 16 or 20 gauge, five or six
inches long, the bundle about 1/2 or 5/8 inch in diameter. As I said
before, a really great source of gadgitry!
I never did figure out how the magneto worked, but a major part of
it was a series of about 12 "V" shaped permanent magnets, maybe 3/8 x 3/4
inch in section, some 4 inches from tip to apex, and 2 inches from tip to
tip, bolted on the flat face of the flywheel. There obviously had to be
some sort of wire windings some where to complete the rig, but I don't
remember anything about it, I just remember the magnets as being great toys,
but not very plentifull, after all, not many engines were ever
scrapped...they could always be repaired.
I also remember how much fun one could have with a spark coil, two
insulated wires and a six volt battery. Brother Bob didn't really
appreciate being waked up with one spark wire to one big toe, and the other
touching his other big toe!
The above is really a hope that somebody out there can/will help me
fill in some of the gaps in my memory of the Model T Ford ignition system.
Send comments to Dan Machesky at dan@beesky.com