John,
With me being one of the 'ole farts around here at 46, I lived through the era
of points. I have learned about them from a technical standpoint, and put up
with them from a maintenance standpoint. While I am sure I don't know
everything, and someone can add to this, I do think I can answer most of your
question.
Here's the scoop on points: Points
rub up against a mechanical device on the distributor shaft that has high points
followed by flat sections. There is a plastic or nylon rubbing block
that spring loads up against that mechanical device. As the
distributor shaft turns, the points open and close, which makes and breaks an
electrical connection from the battery to the coil. This opening and closing of
the points sends current through the coil then stops. The coil's job is to take
that little bit of current that the points allow to pass through from the
battery and jack it up to create a large voltage that can jump a gap in the
spark plug. Those old coils would generate somewhere between 13,000
to 20,000 volts if memory serves me right, with 20,000 being the most
common.
The points weakness were as
follows:
1. When you reached higher rpms
points would tend to "float" because they couldn't follow the shape of that
distributor lobe (wouldn't be able to close all the way for as long as they
should) when things were traveling that fast. Therefore they didn't do a
very good job at higher RPM's at keeping the coil supplied with what it needed
to put out a good spark. The hot rodders used dual point distrbutors to try
to get around this problem. It helped, but couldn't eliminate the problems I am
about to describe.
2. The plastic/nylon rubbing block
would tend to wear as time went on. While you were supposed to grease the
rubbing block to help reduce wear, it still had wear happen eventually and as
such ..the points got out of "adjustment"...or wouldn't work at maximum
efficiency.
3. The amount of gap that the points
opened had a lot to do with time open and closed and that had a lot to do with
the right amount of current being sent to the coil. So you had to adjust the
points gap.....not just when you changed them......(which is a big hint of
things to come), but point gap was constantly changing from the time you put
them in. In fact, you had to initially set them to a certain amount of gap when
the plastic/nylon rubbing block was on a high point on the distributor lobe. So
you needed a "feeler" guage (little pieces of metal of exact thichnesses and
marked on them as to thier thickness) that set them to an exact amount. In a
pinch, if you didn't have a feeler guage, and you were in an emergency "get it
running and to hell with accuracy" situation, the ole boy's rule was to use a
match book cover as the guage. GM did lead the way here and came up with a way
to adjust points using a meter that measured what was happening at the coil.
They also put a little "window" in the distributor cap where you could reach in
with an allen wrench and adjust the points while the engine was running while
looking at the dwell meter. I don't think Ford or Mopar ever did follow the lead
on this.
4. The reason the points needed to be
adjusted often was that the gap ...which directly related to time open and
closed....called points "dwell" ...changed due not only due to the wear of the
plastic/nylon rubbing against the metal block, but the metal contacts of
the points would also get pitted from the constant pounding of current starting
and stopping through them. Sometimes they would get so bad the car wouldn't run.
So they had to be changed periodically ..and/or adjusted......and adjusted
.....and adjusted.......being the main cause of the need for a "tune-up", which
was much more often then than they are now due to points style ignitions being
so bad.
Now, considering that today's HEI systems
no longer use points ...and use a much more effiecient electronic system for
controlling the current flow through the coil, there is nothing to wear out,
nothing to go out of alignment, no "float" at high rpms, nothing to change
due to wear, and nothing to adjust. The coil is also jacked up from
the old 20,000 volts to between 40,000 to 50,000 volts. This allows you to have
a wider gap in the plugs than back then, and a better ignition source (long
strong ZAP across the spark plug) for lighting up the gasoline & air
mixture.
For me the points go in the
trash! I will NEVER go back to points...TECH RULES in this
case!
Correct me if I am wrong
guys...
Steve
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I hear alot about HEI , not familar with that application. Can someone tell me the advantages and disadvantages of switching from points to this ? I hear alot of differnet stories about this , need more insight.
Thanks...John
I hear alot about HEI , not familar with that application. Can someone tell me the advantages and disadvantages of switching from points to this ? I hear alot of differnet stories about this , need more insight.
Thanks...John
