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Re: GM HEI Coil Autopsy



On Sun, 15 Nov 1998 21:38:00 -0700, you wrote:

>Original Poster: Terry Fritz <terryf-at-verinet-dot-com>
>
>
>Hi All,
>
>	I used vicious cutting machines to slice the failed GM coil in half.
>These babies are built like rocks.  Extremely difficult to cut open.  I was
>not able to find the exact failure site however the following was learned.

>
>	There are two problems, however.  There is a design "flaw" in the primary.
> The primary is two layers thick with both terminations on one side.  They
>spin the first layer and then spin back over the first layer to the
>beginning.  This allows the entire primary voltage to be placed across
>adjacent wires at the begining (or end) of the primary.  Normally, 12 volts
>probably isn't a problem.  But in my case, I have to be sure the voltage
>across the primary does not get too high.  I'll probably put an 1800 volt
>MOV across the next coils' primary.  If they would have put an insulating
>layer between the two layers this coil would be much more reliable
>espicially under unusual conditions (like a spark plug wire falls off the
>plug) (I hope Delco is listening ;-)).

I've not had an ignition coil apart, but I'm assuming it's a
cylindrical form with central core - if so, surely you could easily
overwind a suitably insulated new primary.