A Dissected Ignition Coil

I have a project where I need core laminations from an ignition coil. I started with a coil I found in my coil box that was leaking oil from the tower. What was inside is worth sharing with pictures. I made a cut around the top rolled edge to open it. It was nearly full of light oil, that was difficult to wipe off surfaces, it just kept coming back.

Here are the parts pulled out of the can:View attachment 20150901_141253.jpg
At the upper left is coil can, under that are two half cylinder shields, then a brown paper insulator. The coil/core assembly is on the right. The outer coil is part the primary, it is formed of multiple winding sections, each separated with paper insulators. There is a second group of windings for the secondary inside the primary bobbin. The secondary windings are done using smaller diameter wire, with more layers, so the number of turns is about 100 times that of the primary.

This is an end view showing the winding construction. The square metal part is the core laminations.
View attachment 20150901_141535.jpg


The core conducts the tower potential, it is insulated from the bottom of can with a white ceramic insulator shown in the top photo. The insulator also serves to locate the bobbins in the can. The outer side core laminations were bent sightly, to make a mechanical connection to a leaf contact on internal tower. The coil+ terminal is the common connection, for the primary to secondary auto-transformer.
View attachment 20150901_141941.jpg View attachment 20150901_141647.jpg

One of the most common coil failures is a turn to turn short in a primary winding. The enamel insulation on the copper wire serves as the insulator. If winding is overheated the enamel burns, a shorted turn consumes a huge amount of current resulting in failure of normal coil operation.