Hi
when coil gets hot car does not start. I assume I can open coil somehow and check windings for continuity. Any comments appreciated
Ken 45145

You can open the coil (remove the top)and replace the condenser. That is the limit as to what you can do. I assume you have the round resistor on the top of the coil?

Do you have one of the original cardboard type coils? Or is it a modern sealed unit? The original can have the top removed but the modern is not repairable.

they appear to be cardboard , I have 2. I attempted to bench test them with my multi meter. I have the understanding that reading from small post to small post I should get a small number measured in ohms. then reading from small to large coil wire i should get a substantially larger reading. it seems everytime i do this i get a different number. on some coils I get 1 testing from small post to large coil connection. I am told that these are nfg. I assume that having original configuration is most desirable
perhaps I should open one up, I assume that grinding top round headed looking fastners the top will come right off. apparently under I will find a condenser. I will have to review my notes on testing that but I think the ohm meter on good condensers reads 1.
one of these days I will understand electricity.
Ken 45145

Ignition coils are nothing more that step up transformers. There are two coils of wire one on the input and one on the output. failure can occur when the dielectric (insulation) on either the wire or between the two coils breaks down and shorts at some point. another failure point can be a broken wire inside the windings or at a terminal. Cardboard is good at sucking up water and become conductive. That would definitely cause a short.

What you intend to do does not sound correct. Do you have an original coil with a bakelite top held on with a center bolt with nut? There will also be a round resister bolted to the top.

If this does not describe your coil, stop, you can't get inside.

Ken
You should get a reading between the 2 small (6v) terminals on all coils. But some will give a reading between the 6v and high tension (different reading on each side) and no reading to the case, while others will be no reading to 6v but a reading to the case, depends on the connections inside which generally means destroying the coil to see.
You need a circuit for 6v (through the points) and a circuit for the high tension (out the top and some back through the case and others back through the points).
If there is a short within, between the windings or either winding and the case the coil will not work properly if at all.
Tony

Ken,

Here is more than you ever wanted to know about testing a condenser.

http://www.hmvf.co.uk/pdf/TESTINGCONDENSERSRW.pdf

I have a Heathkit Condenser Checker that I use in my antique radio radio repairs although I have never used it on an automotive condenser. For my '37 they are cheap, so I figure why not just use a new one. I do know that a condenser will fail over time even if not being used. I would not think it would be appropriate to use a NOS unit.

Rich