Robert Allen wrote:
> causes the secondary field of the coil to collapse also, and a big spark
> spits out of the top of the coil. This leads to the center of the
> distributor cap which connects to the hat atop the rotor, and now the
> rotor is looking for someplace to release the voltage.
>
> This happens as soon as the rotor swings around to an electrode inside
> the cap. Boom! A sparkplug ignites.
That's simply not true. The voltage will not "sit" on the rotor
waiting for the proper gap before firing.
The voltage appears at the rotor when produced by the coil. It
will either arc to the metal if the metal is close, or nothing
will happen. It will not "sit and wait" and screw up your timing,
that's simply not possible.
> Also, as welders know, the longer the air gap, the more amps
> needed to make the jump.
Not amps, volts. The longer the air gap at the same voltage
will flow fewer amps.
More to the point...
The reason that wobbly shafts cause spark scatter is because
the cam on the shaft physically opens the points by pushing
on them. As you know, the amount of "push" is actually a
very small distance sideways, in other words in a direction
where the shaft shouldn't move a bit but will move when
worn.
If the shaft is perfectly solid and brand new, moving the
points cam a fraction of an inch is not a problem, it is
precise and reliable.
If the shaft is worn, the effort required to push the
cam also moves the shaft in it's loose bushings, and
the points don't open exactly when they should or even
exactly the same time every spin. Since the
amount of "give" the shaft has is variable because of
wear, the point opening time varies.
Electronic ignition solves this problem because lateral
movement of the shaft does not affect the triggering time,
only the air gap (magnetic) or the cut point (opto). Neither
affects timing as long as they stay within enough tolerance
to still trigger.
--
Trevor Boicey
Ottawa, Canada
tboicey@brit.ca
http://www.brit.ca/~tboicey/
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