creating a charge with an electromagnetic field between the primary and
secondary windings. This charge is built up when the breaker points are
closed. When the distributor cam opens the points — when the cam
comes around with one of its four, six or eight, lobes (depending upon
how many cylinders the engine has), the electromagnetic field within the
coil collapses, creating the high-voltage impulse. Again, the breaker
points are nothing more than a switch that loads and fires the coil.
However, it is an important switch that must be properly set, maintained
and replaced when it begins to fail.
Why do the points need to be set? The electromagnetic field within the
coil is built up, or loaded, when the points are closed. When the points
open, or “break,” the field collapses and the coil is fired. As you may
imagine, this process happens very fast when a vehicle is roaring down
the highway. If the points are not set correctly and open the correct
distance when a distributor cam lobe comes around, the coil may not
have enough time to build up a full charge. This results in a weaker
spark or no spark at all, and the engine will lose power or misfire.
Breaker points that slip out of adjustment because their mounting
screws become loose — as happened on my M38 — may not close, and
the coil can’t build up a charge. On the other hand, if the points don’t
open, the charge can’t be fired.
Breaker points are opened by the distributor cam lobes pushing
against a rubbing block. Naturally, this rubbing block gradually wears
away, which means that the breaker point contacts don’t open as far as
they did when the block was new. This is why the points need to be
checked and/or reset at regular tune-up intervals, which are found in
most vehicle manuals.
In addition to the rubbing block wearing away, the breaker point
contacts are gradually eroded and/or become burned by the electric
current flowing through them. You may have heard someone talking
about “dirty points” as being the reason their car or truck wouldn’t start
or run right. Breaker point contacts can also become corroded, especially
on vehicles like hobbyist MVs that are driven infrequently. Breaker
points may also become dirty because there is oil in the distributor,
someone put too much lubricant on the cam or used the wrong type of
lubricant.
singke
(singke)
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