What is in ignition coils ???

Just want to learn anything We can on this subject ....in our attempts to resurrect some motors around here, We have noticed that some coils have a Bouyant liquid feeling when handled , some will rattle as if there are crystals(sand ),, and some feel no movement at all when handled, Doubtful ,if a coil can be ruled unfit simply by the way it feels ,,

(quoted from post at 10:13:32 12/03/09) Just want to learn anything We can on this subject ....in our attempts to resurrect some motors around here, We have noticed that some coils have a Bouyant liquid feeling when handled , some will rattle as if there are crystals(sand ),, and some feel no movement at all when handled, Doubtful ,if a coil can be ruled unfit simply by the way it feels ,,

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aven't seen in every coil in the world, but have found oil, epoxy, tar, hard wax-like-plastic material, and when very oil, some have had the hard materials broken/cracked & in chips or chunks. I think that is what you are asking about, but the other 'insides' are iron core, copper wire wound around core (primary & secondary windings).

I think over the years that substance has changed and improved. I believe at one time it was the fairly liquid oil type substance that may have contained PCB (big transformers used such anyway) and when it was banned (and/or even before) it was a thicker gooey more like tar based filler. Of course when they have that classic burned electic hot smell and any of that sticky gooey oil has leaked out THATS NOT A GOOD THING.

As a preliminary test if theres no classic hot burned electrical smell,,,,,,, or any evidence of leaked oil,,,,,,,,, Id measure the LV Primary between the little + and - terminals and Id expect it to be in the 1.25 to under 4 ohms range (depends on if 6 or 12 volt coil),,,,,,,, while the resistance of the HV Secondary measured out the top HV Tower may be in the 5k to 10 k ohms range. If it passes allllllll those tests theres a chance its a good coil HOWEVER it can pass all those and still be bad due to HV breakdown once or even before its warmed up i.e. these simple low voltage tests can tell you if its bad BUT NOT IF ITS GOOD.

Of course theres the lesser length of bigger wire LV primary coil windings and the many more turns and length of smaller HV Secondary wire coil windings all immersed in that nasty "oil"

If none of that works for ya put it on a bench with some jumper wires and hot wire it to 6 or 12 volts and see if it will fire a spark plug via a wire out the top HV tower once its on (conducts current through primary) then switched off. Be careful theres HV floating around ya know you may get bit .......

"Stop Global Whining"

John T

thanx John , And everyone else for the education ...

The older coils where filled with a tar like stuff and the newer ones are filled with oil. Both can/will do funny things if left with the switch on and the engine not running. The ones with tar can/will swell and cause the tar to boil out and the ones filled with oil can/will explode and make one heck of a mess. I learned about the exploding coil back a few decades ago on a VW bug and left the key on with a 12 volt battery on a 6 volt coil. The coil exploded and sounded like a shot gun going off