Morris Minor Owners Club

I've noticed in a couple of posts recently that I should NOT be using a ballast coil, however my coil is a ballast type

It seems to work but it does get hot, especially if the engine isnt running ... what damage am I doing and to what parts?

The Mini boys will confirm but if I remember rightly a ballasted coil is designed to run on 9v and the normal Moggie coil is 12v so in theory you are giving the coil too much voltage which will shorten its life span. You will prob get a good meaty spark from it though

The coil will get too hot and fail.
The ballast coil is designed to work on 9 or so volts when starting. When the engine starts the 12 volts goes through the ballast resistor and the coil see the 9 volts it was designed for.
All coils get hot if the ignition is on and the engine not running. It is bad practice to leave the ignition on without the engine running.
If you want to listen to the radio when parked then wire it to the always live side.

I have my 'radio' on a push button separate from the ignition, but thanks guys .. I should leave the coil I have on and keep a spare in the boot for WHEN it dies (I'm pretty sure I have a spare or two lying about)

No - take it off and fit another, because it WILL fail at the most inopportune time/place. Or - wire it correctly with a ballast in the circuit to give 9 volts - and a direct feed activated by the starter solenoid (you will need a relay) to boost it when starting. That's it's intended method of use.
At the moment it is passing far more current than it should - which is heating it up, but also seriously overloading the points and the condenser. There WILL be trouble ahead!

OK, point taken ... thanks for the advice

Don't forget to try the spare coil first, and not just assume it's okay. In fact, run with it for a while, to make sure it's not getting hot too.