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MG Midget and Sprite Technical - Very Hot Coil

HI

I Own a 1974 Midget RWA

Currently the car is off road last time i went out in it , it broke down on me had to call road side assistance but what came out of it was the Coil which has just been replaced was very very hot even after a hour

The car had run okay but for approx 30 mins went through the geras well even at low speed but just started to deteriate until it ground to a halt , this is the 2nd time it has happened but when i leave it for a short time , it starts up okay , i did this when i had the old coli in also

Any body got had ideas what it could be suppose it must be electrical around the coli , but why would it run okay for a short while then start to run like a dog

Thanks to all those that reply
g payne

I had this happen once - identical symptoms - and it turned out to be a faulty coil. From what you say though, you have the problem occurring with different coils, so perhaps the problem lies elsewhere. I'm sure others will be forthcoming with advice.

Simon
SA Wood

A coil gets hot when it carries current - i.e. when the ignition is switched on and the coil is connected to earth. This is normal - although intermittent; on-off, on-off etc! - via the points when the engine is running.

Or the coil may be getting hot because of an internal fault - poor insulation which breaks down as it warms up. Hence the delayed appearance of the fault.

Or it could be that it is still hot "even after an hour" because with the engine not running the ignition was still live. Or maybe the "output" side is earthing when it isn't supposed to be. Check the points gap is right. Also, has a PO fitted an earth switch immobiliser to the ignition circuit?
Guy W

just a thought..have you fitted a 'ballast' coil.
I dont know how long they would run without the ballast resistor. It would certainly run hot
a boyle

RUN ...DONT WALK.. RUN... to the car immediately

Pull the battry cables....my guess and its a good one from past postings

You have a damaged / rotting wiring harness

Concidering that it runs fine for 1/2 hour then runs like trash is a strong indication of a issue in the ignition wire that runs thur the tach from the coil

Its one of several possiabilities

Wire got pinched, you put a screw into it recently thur the fire wall, or the wire insulation has worn and is chaffing on bare metal edge....

at some point, in the length of your ignition wire your going to find bare wire strands rubbing against bare car metal

Find that and your good to go

But seriously...disconnect the battery right now ...sudden fires are not uncommon in this situation, esp if the ignition wire gets so hot that it melts and cause other wires to melt in the harness.

Good luck

Prop
Prop and the Blackhole Midget

Sorry... I should have asked 1st

1st ...check your ignition wire from the coil to the tach after a 1/2 hour of running also...is it really hot as well??

If it is...then panic for fear of fire

Make sure you got plenty hotdogs and marshmellows for supper tonight...im sure the neighbors will want to join in.

Prop
Prop and the Blackhole Midget

Sounds to me like you've fitted a 6 volt (ballasted) coil to a non-ballasted system.

The ballast is usually a big white ceramic block that's attached to the coil. If you've got no ballast, you need a 12 volt (unballasted) coil. A 6 volt coil will overheat.

That said: you've tried it with both the old coil and the new one and the symptoms are the same. Now, It's entirely possible the old coil was the wrong type too, but I'd be checking the condenser inside the distributor too.
Growler

Hi
Almost exactly the same symptoms as my MkIV Sprite when I first got it last year: Run for 20 to 30 minutes, start to run a bit rough and then cut out, especially if stopped at a junction. The coil would be very hot. Wait for 20 minutes for things to cool down and set off again.

A new coil and condensor made no difference. A new red rotor arm from MGOC cured it for me. I haven't checked how hot the coil is recently as everything in that department seems to be running OK now.

Colin
Colin Mee

This thread was discussed on 11/06/2013

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