Folks,
If you have problems with starting or a high speed miss then you
may have a postive polarity spark. This will also cause the side
electrode of your plugs to "dish". The spark should always have
negative polarity. To check the polarity of the spark, remove
a spark plug wire and hold it about 1/4" from ground. Insert the point of
a common lead pencil in the gap between the plug wire and the ground.
While running the motor, if the spark flares on the ground side of the
pencil lead then the polarity is correct. If it flares on the plug wire
side then you have reversed polarity. Simply switch the two low voltage
coil wires to correct the problem.
Recommend that you not ground your self to the car while
doing the test unless you want a shocking experience.
This spark thing may be why the old cars had postive
ground. Some one knew that the ground side of the plug
should be postive relative to the plug electrode. Therefore it
seemed logical to have the battery connected as postive ground.
The Model T Ford used a continious vibirator activated
spark coil. I do not know if one could change the polarity
of the spark using this setup. I believe that the spark was
more like AC than a DC pulse. Therefore a postive battery
ground gave better ignition on the Model T ?
I assume that the ground was changed to negative to
minimize corresion on other parts of the car. This is a
wild guess. Another guess is that the diodes in alternators
were cheaper with a negative ground.
Generators can produce either postive or negative
depending on the initial magnetic field. This is why
you must "polarize" a new or rebuilt generator. Touch
a jumper wire between the battery terminal and the
armature terminal for a fraction of a second and you have properly
polarized the generator. Do this after replacing the
regulator as well. Note that if you hold the jumper wire
on for more than a fraction of a second you may fry
the regulator and burn your fingers too.
James Barrett Tiger II 351C and others
|