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Ignition coil overheating

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Old Aug 6th, 2017, 19:05   #1
arcturus
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Default Ignition coil overheating

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.
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Old Aug 7th, 2017, 10:58   #2
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Done some research.looks like a ballast resistor might help if not already fitted.
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Old Aug 7th, 2017, 12:30   #3
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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.
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Old Aug 15th, 2017, 21:17   #4
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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.
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Old Aug 15th, 2017, 21:47   #5
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Quote:
Originally Posted by blueosprey90 View Post
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/
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Old Aug 19th, 2017, 21:06   #6
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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?
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Old Aug 19th, 2017, 21:54   #7
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I've had a load of experience of synchronising dual points on early PRV engines. Tell me, on the Bentley, is one of the point sets gap adjustable from outside the distributor?

Salut!

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Old Aug 19th, 2017, 23:21   #8
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http://rrtechnical.info/mkvi/wshoplate/12.pdf

read carefully, easy job.
regards, Kay

.015 is not enough, dwell is too high, coil wil overheat
.019-.021 dwell 42°
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Old Aug 20th, 2017, 03:14   #9
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Thanks Kay for your interesting post. Unfortunately in this case my experience is of no help.

Salut!

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Old Aug 21st, 2017, 10:44   #10
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Quote:
Originally Posted by mocambique-amazone View Post
http://rrtechnical.info/mkvi/wshoplate/12.pdf

read carefully, easy job.
regards, Kay

.015 is not enough, dwell is too high, coil will overheat
.019-.021 dwell 42°
For six cylinder should be around 30*
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