In a message dated 97-08-31 23:12:20 EDT, tboicey@brit.ca (Trevor Boicey)
writes:
> Remove the coil + wire, turn on ignition, and touch and
> remove the + wire to the coil. You are in effect simulating
> the points, and should make a spark.
Trevor:
I agree that if you get a spark this way, it is a pretty sure sign the coil
works at least some time, but if you don't get a spark, I don't think you can
say for sure that the coil is bad. What about the points and the capacitor.
The points might be open, and they might be closed. If they are open, you are
charging through the coil and the capacitor in series, and current will cease
through the coil when the capacitor is charged, and there will be no field to
collapse to produce a spark. When you remove the + lead, it will be the
discharge of the capacitor, through the coil, rather than the field collapse
of the coil, that tries to produce a spark. The discharge of the capacitor
will provide a very small current, and a corresponding small magnetic field
buildup.
If the points are closed, when you remove the + lead, the capacitor is not
there to provide a discharge path for the coil, and the field collapse will
not be nearly as rapid as required to produce a good spark. Contrary to
popular belief, the capacitor is there for more than just to protect the
points.
For a discussion of this subject, go to :
http://www.vtr.org/maintain/ignition.html
A better way to test, I believe, is to connect a spark plug to the HT
terminal of the coil, as you described, and open and close the points using a
small piece of wood to prevent any possibilty of a shock. This tests not only
the coil, but also the capacitor, which is a drawback. Either one being
faulty could cause the test to show up negative.
Comments? The above is theory - practical experience may over rule.
Dan Masters,
Alcoa, TN
'71 TR6---------3000mile/year driver, fully restored
'71 TR6---------undergoing full restoration and Ford 5.0 V8 insertion - see:
http://www.sky.net/~boballen/mg/Masters/
'74 MGBGT---3000mile/year driver, original condition
'68 MGBGT---organ donor for the '74
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