It is easy to replace the coil but I suspect the voltage regulator, probably
a zener diode, is getting loose (bad solder connection since the problem is
intermittent) and should be fixed first. If the voltage is too high then the
secondary/high voltage will be higher also and may be breaking down the
insulation and shorting to ground causing the hi - rev miss.This could be at
the coil, the HT wire to the Distributor, thedistributor cap, the HT wires
to the plugs or the plugs themselves. Fix the over voltage problem first
then worry about the coil if you still have problems.
----- Original Message -----
From: "John Hobson" <goalie_john@yahoo.co.uk>
To: "Richard B Gosling" <Gosling_Richard_B@perkins.com>; "spitfires"
<spitfires@autox.team.net>
Sent: Tuesday, November 28, 2000 8:09 AM
Subject: Re: warning light and alternator
>
> Is a new ignition coil easy to fit (in comparison to fitting my
alternator,
> which was simple)? Is there any way to test wether the current one is
shot?
>
> cheers
> John
> ----- Original Message -----
> From: "Richard B Gosling" <Gosling_Richard_B@perkins.com>
> To: "goalie_john" <goalie_john@yahoo.co.uk>; "spitfires"
> <spitfires@autox.team.net>
> Sent: Tuesday, November 28, 2000 3:38 PM
> Subject: Re: warning light and alternator
>
>
> > John,
> >
> > I would agree that 16.9V sounds too much. The cause of this is almost
> > certainly the alternator - this is all the more likely because you took
a
> > working, used one, rather than a reconditioned (i.e. good-as-new) item.
> If I
> > understand it right, the alternator generates voltage proportional to
the
> > speed of the engine; it is then corrected to the desired output by some
> > electronics in the back of it, which also converts the electicity
> generated
> > from AC to DC. If you are generating that high a voltage, I would
> suspect the
> > electronics in the back of your alternator are dodgy. It will work,
but
> it
> > will damage components due to overheating over time. I'm also not sure
> what
> > the effect will be on your battery of having that high a voltage across
> it for
> > a sustained period - it might overheat the battery. Have a feel of the
> > battery casing after a long run.
> >
> > As for the coil, this is a cylindrical thing that is bolted onto the
> bulkhead
> > near the battery, with a connection at each side of the end, and one
from
> the
> > middle of the end. This generates the very high voltage needed to make
a
> > spark in your spark plugs. There are actually two coils inside it.
The
> first
> > is connected to the live supply from the battery. It is then earthed,
> via a
> > switch in the distributor. The coil has electricity passing through
it,
> which
> > builds a large magnetic field within the coil. At the crucial moment,
> the
> > distributor opens the switch to earth, so no more current can pass; the
> > magnetic field immediately collapses. This sudden change in magnetic
> field
> > strength creates a current in the second winding, with a very much
higher
> > voltage. The current is very low, but that's OK. The current flows
> along the
> > HT (high tension, which actually means high voltage) lead to the top of
> the
> > distributor, which sends it to one of the spark plugs, and this current
> leaps
> > across the spark plug gap to cause the spark. The distributor then
> > re-connects the LT (low tension, i.e. low voltage) side of the coil, to
> build
> > the magnetic field once more.
> >
> > This can cause poor running at high revs because, if the first winding
is
> > dodgy, it may not have time to build much of a magnetic field at high
> revs
> > (the faster the engine, the less time there is between sparks). There
> will
> > therefore not be much of a current generated in the HT circuit, so the
> spark
> > at the plug will be weak. However, this is but one of a number of
causes
> of
> > poor high speed running - timing out, centrifugal advance on the
> distributor
> > (which makes the spark earlier at high speeds, to give the petrol more
> time to
> > burn) not working, partial fuel blockage, weak fuel pump, mixture
> incorrectly
> > set on carbs for starters. My instinct is that electical drain is not
> the
> > most likely cause of your high speed running problem, but is competely
> > separate, or is simply paranoia as you said!
> >
> > Well, that may be more than you wanted to know about coils, but you did
> ask!
> >
> > Richard and Daffy
>
>
> __________________________________________________
>
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