Coil very hot and difficult starting

[Leyland]

Hi all
This week got engine running after years of a rebuild. Ran reasonable at the beginning for 10 mins or so. Now very difficult to run. Not sure electrical or carburettor.
However, I have noticed that while trying to start engine coil is getting very very hot. Is this right. It is a new Lucas coil. Am I right with my connections CB (white/black wire goes to + on coil and white goes to - on coil. The old. Oils used to be marked CB if I remember. My car is positive earth would that make a difference to connections. As I say the coil is very hot to touch after a few minutes of trying to start engine. Could I have another duff Lucas coil. Any advice welcome please
Ty

[myoldjalopy]

Yes, you have wired it correctly - if your car is +ive earth then the +ive terminal on the coil (CB) goes to the dizzy as that is where the current goes to earth via the points. The -ive terminal on the coil (SW) is where the feed from the ignition side is attached. Vice-versa if your car is -ive earth. I suppose it could be a duff coil......there are plenty of stories of modern 'Lucas' coils playing up. Someone else on here will know various reasons of why a coil might get too hot. Hopefully, they will be along in a bit to advise further

[Leyland]

I have read somewhere that if you leave the ignition on without the engine running the coil gets hot. I have been leaving the ign on while trying to make adjustments. I will look at fuel next as having problems starting. It starts and runs a few seconds and dies. Electrical side seems to be working. Ty

[pgp001]

The coil will heat up if the points are closed and the ignition is on, it is like a little mini electric fire in there I suppose.
I had coil overheating problems myself recently but that was during normal running, it turned out to be a faulty Lumenition electronics pack.

I have since fitted an Accuspark distributor and coil and it works a treat without getting hot.

Phil

[oliver90owner]

Deleted

[oliver90owner]

Deleted.

[oliver90owner]

I have read somewhere that if you leave the ignition on without the engine running the coil gets hot. I have been leaving the ign on while trying to make adjustments. I will look at fuel next as having problems starting. It starts and runs a few seconds and dies. Electrical side seems to be working. Ty

Not necessarily so. It depends entirely on whether the contact points are open or closed. If closed the coil will pass about 4 amperes. That is ~ 50 Watts. Little wonder it gets hot! If points are open, there should be no current, so coil should not get hot.

While the engine is running, the average current through the coil is far less. Firstly because thepoints will be open part of the time and secondly because the coil is an inductor, and as such will oppose any change in current when the points close.

It will make little difference which way they coil is wired, re heating. But the spark energy will certainly be affected.

Connecting the coil the correct way is simply following the convention of more positive volts is connected to the positive side. Think here posite earth means live is negative 12volts and negative earth means live is positive 12 volts. +12 volts is a greater value than -12 volts. Simples, really.

So your problem could be one of excessive dwell angle - the points are closed for far too much of the distributor rotation.

It would be good to measure either the current flowing though the coil (engine not running) or the coil resistance as a first check. Don’t jump straight to incorrect conclusions!

What colour is the spark, by the way? There is the possibility of a failing condenser, so a simple colour check can resolve that.

Better to sort out whether it is electrical, or not, first (checks are simple, easy and definitive) before altering all and sundry items in a non-systematic way.

PS. I thought I posted last evening, but either lost to the ether or someone thought it was too technical for the forumers.


Sent from my iPad

[Leyland]

Many thanks Oliver for very helpful reply. Ty

[Ian Jones]

Coils come in a variety of resistances. The ones used in conjunction with some electronic ignition systems have a resistance of around 1 ohm which, if used with standard ignition will mean about 12 amps. They will get very hot. Don't ask how I know! Your coil with standard ignition needs to be 3 or 4 ohms, giving a current of 3 or 4 amps. They will still get hot if left with ignition on and points closed, but not blister your finger hot. Again don't ask how I know. My Austin 10 used to have electronic ignition.............

Regards

Ian