Practically Classics Forum

Can anyone tell me why my ignition coil gets very hot almost untouchable when the ignition is turned on without engine running, have checked wiring polarity + to 12 volt supply - to Distributor, this is a newly built engine so has only just run for 2 - 3 mins

I was taught not to leave the ignition on without the engine running to prevent damaging the coil. Why is it something you want to do?

It gets hot because the engine has stopped in a position such that the points are closed. With the points closed of course there is quite a large permanent current flowing through the primary of the coil, so it's gonna get hot, VERY hot. For this reason you should never leave a conventional points-and-condenser car for long periods with the ignition on but not running. You'll also get a flat battery in fairly short order too!

If there's some specific reason why you need to do this you can rotate the engine until the points are open, or simply disconnect the feed to the coil.

Beware that if you've severely overheated the coil, it may have failed or it may do so before long.

I suppose you're not using a coil designed for electronic ignition on a points car are you? Or a coil designed for use with a ballast resistor when none is fitted?

I agree with all the previous comments but would add that coils do run hot anyway. Various measures are taken to insulate the casing including enclosing the coil in an oil filled jacket and they should be sited clear of wiring and engine bay clutter to avoid heat damage to other components.
You wouldn't put your hand on a hot radiator so hugging a coil is an equal no no

Thanks for all replies, I thought it had something to do with points closed, I needed the ignition on for a while as I was testing electrics on the fuel pump, sender unit etc, will remove supply to coil in future, can anyone recommend a good carb balancing kit ?

I have one of these (or something suspiciously similar)
http://www.fastroadcars.co.uk/shop/inde ... ductId=209

Which I used when I was running twin SU HS2 carbs on my mog. It made life much simpler!

I have the Gunson "Carbalancer" or whatever it's called - I was cynical at first, but when I used it, it proved to be an excellent bit of kit, and not expensive.