Ignition coil overheating

[arcturus]

Hi, have been talking to a friend who had an old Bentley MKV1 12 volt, who is having problems with overheating coils, to hot to touch. I said that I would ask around to try to find some answers. I know it's not a Volvo but a coil in general is a coil. Can any body point me in the right direction? I believe some coils need a ballast resistor.

[arcturus]

Done some research.looks like a ballast resistor might help if not already fitted.

[Derek UK]

The Bentley uses a basic 3 ohm coil with internal ballast. If a 1.5ohm coil is fitted without an outside resistor it will run very hot and die pretty quick. If you have a spare for the 144 perhaps let him try that. Might need to adapt the pos and neg tabs and maybe the main coil wire fitting if his is currently a screw on type. No big deal though.

[blueosprey90]

I'm new to the Volvo world, but I own an '59 MGA on which I run a 3 ohm Lucas sport coil. This is a coil designed for a 12 volts non-ballasted ignition system. The coil has a primary resistance of about 3.2 ohms. A coil for ballasted ignition system will have primary resistance of about 1.6 ohms.

You can measure the coil with an ohmmeter or multimeter.

In my experience, when a coil is too hot to the touch, it is failing. Inside the coil is an oil that is supposed to keep the coil cool. When this gets so hot that one can't touch the coil, there is something wrong internally and it may only be a matter of time before there is complete failure. My cases have usually started with a misfire under load.

[v8250]

Originally Posted by blueosprey90

I'm new to the Volvo world, but I own an '59 MGA on which I run a 3 ohm Lucas sport coil. This is a coil designed for a 12 volts non-ballasted ignition system. The coil has a primary resistance of about 3.2 ohms. A coil for ballasted ignition system will have primary resistance of about 1.6 ohms.

You can measure the coil with an ohmmeter or multimeter.

In my experience, when a coil is too hot to the touch, it is failing. Inside the coil is an oil that is supposed to keep the coil cool. When this gets so hot that one can't touch the coil, there is something wrong internally and it may only be a matter of time before there is complete failure. My cases have usually started with a misfire under load.

This+1. Have had similar on a number of classics over the years. Coil manufacturing quality isn't what it used to be. I now use simonbbc for nearly all road car ignition components http://www.simonbbc.com/

[arcturus]

Problem still not solved.Received this message today

Hi George,
Still having overheating coil,,then the misfire starts,,just made it home on 3 cylinders

last time out..I now have 2 coils ohms reading 3.3 and 3.5 other windings are 8k and 9k

new plugs 6 all check out on ohms test
new condenser
1 new coil

checks on battery earth
engine earth
replaced all coil wires from ign.and to distributer
point cleaned and reset to 15 thou points on the regulator cleaned

have no more ideas need Help and more help and then help

regard( hopefully) Leon....

An external ballast has been previously mentioned. What exactly is this. could someone pleas post some details of this with a link?
Whilst researching I noticed that the Bentley has two breakers and they need to be synchronized. Anybody have experience of this?

[arcturus]

Originally Posted by Derek UK

The Bentley uses a basic 3 ohm coil with internal ballast. If a 1.5ohm coil is fitted without an outside resistor it will run very hot and die pretty quick. If you have a spare for the 144 perhaps let him try that. Might need to adapt the pos and neg tabs and maybe the main coil wire fitting if his is currently a screw on type. No big deal though.

Why would a 144 coil possibly work. Does it have an internal ballast. problem still not solved. latest, the car will start but after a very short time coil heats up and starts to miss fire.

to me
Hi me again
I have found that 456 plug are the prob. so something is stopping the

the spark on those plugs. ( today started as i said all 6 running strong then 456 switch
off) any ideas?
I have told him to try fitting external ballast but he is convinced something else is causing problem. Some people won't be helped!

[mocambique-amazone]

Why the hell he trys Autolite 456?? If I remember right they are totally wrong.
Wrong heat range
wrong thread length


ohoh

still the prob with the over heating coil.


I would try Champion RN6YC and no Autolite

Maybe on this engine they used two different kind of plug threads : 14mm and 19mm long. He should get in contact with the bentley drivers. Or buy a good crystal ball of a visionary or should read in cold coffee.


good luck, Kay

[Derek UK]

I think he means cylinders 4, 5, 6. If the Bentley coil is spec'd at 3 ohm the 144 one will also work as that is 3 ohm. If the Bentley coil measures 1.5 ohm it needs an external ballast. Some early cars, all makes, used a circuit that switched out the ballast resistor when the starter was being used to give a fatter spark. It would then switch back to 3 ohm for normal running. Check that this car has this sort of system. That doesn't address your 456 problem. Bentley 6 cylinder firing order is probably 1-5-3-6-2-4. Check that.