Beaverbeach said:

1.6 ohms when hot or both hot/cold?

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It does not matter. The rating for the ballast resistor is 1.6 ohms. This would be measured normally at room temperature, but again, it is the value assigned to the resistor.

Beaverbeach said:

I have run with voltage measured both on the battery and on the coil with around 14V, so no problems there..

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14v is too high for a coil that is not designed for that voltage. A coil designed for that voltage will have a higher internal resistance.

Beaverbeach said:

To me it seems strange to add a ballast to a coil that is not designed for it,

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There are two types of standard coils. Those with the resistance built in, and those that need an external ballast resistor. The coil manufacturer will state this in the specification for the coil.

Beaverbeach said:

Don't remember having this problem on any of my old beetles though..

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I had lots of beetles also. There were two types of Bosch coils for the Beetle. One had the ballast resistor built in, the other needed an external resistor.

Beaverbeach said:

Shouldn't the coil get twice as hot with twice as many cylinders?

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Answer to that is no. Coils are giant condensers. They build and store energy. Typically they will fail in a manner that is noticed at higher rpm as a miss. The coil has lost its capability to build and store the required voltage and can't keep up with the discharge rate at high rpm.

jjacob said:

It does not matter. The rating for the ballast resistor is 1.6 ohms. This would be measured normally at room temperature, but again, it is the value assigned to the resistor.



14v is too high for a coil that is not designed for that voltage. A coil designed for that voltage will have a higher internal resistance.



There are two types of standard coils. Those with the resistance built in, and those that need an external ballast resistor. The coil manufacturer will state this in the specification for the coil.



I had lots of beetles also. There were two types of Bosch coils for the Beetle. One had the ballast resistor built in, the other needed an external resistor.



Answer to that is no. Coils are giant condensers. They build and store energy. Typically they will fail in a manner that is noticed at higher rpm as a miss. The coil has lost its capability to build and store the required voltage and can't keep up with the discharge rate at high rpm.

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Thank you for that informative and helpful post

One other situation that will make a coil overheat on a points ignition system is sitting with the ignition on and engine stopped. If the points are closed the coil is energised and is passing higher than normal current (when running the inductance of the coil reduces the current - dI/dt but this does not happen when the engine is stopped only the resistance of the coil limits the current). This effect is worse with non-resistor coils. A resistor coil will heat most at high revs.
Note that non-ballast coils don't have a physical resistor inside, they just have more turns of wire (and/or thinner wire) on their primary winding.
If the coil is designed for a resistor, it should be fitted. Not doing so stresses the whole ignition system, not just the coil.


Robert G8RPI.

jjacob said:

-Generator or Alternator is overcharging the system. This is an indication that the voltage regulator has failed. Check the voltage at the battery while the engine is running at 2000 rpm. Voltage should be between 13.5 and 14.4 volts. If you see 15+ volts you should replace the voltage regulator.

John

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Thank-you John.
I don't have the coil problem although I notice the transfers on it are warping with heat and although I identified the rocker arm problem, it was mentioned that a overheated coil will let you down and cause a miss at high revs.
So I checked the output from my dynamo....way over 15 volts when the engine is racing.
That explains why it fried the output terminal a short while ago and why the battery acid suddenly decided to evaporate and why the headlights are so good at the moment.....it all makes sense now; why didn't I see it.
I will probably go for an electronic regulator rather than try to mess with the old one. I remember years ago having a pre-war car on which I could never get the charging right, so I'm going for the easy option.

fiat500 said:

Thank-you John.
I don't have the coil problem although I notice the transfers on it are warping with heat and although I identified the rocker arm problem, it was mentioned that a overheated coil will let you down and cause a miss at high revs.
So I checked the output from my dynamo....way over 15 volts when the engine is racing.
That explains why it fried the output terminal a short while ago and why the battery acid suddenly decided to evaporate and why the headlights are so good at the moment.....it all makes sense now; why didn't I see it.
I will probably go for an electronic regulator rather than try to mess with the old one. I remember years ago having a pre-war car on which I could never get the charging right, so I'm going for the easy option.

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Peter, if you have identified any visual issues with the coil you should really replace it, they are cheap. Overcharged coils will ultimately fail.
The only reason not to use a solid state regulator is because you can't get one! You are wise to go that way. Fiat certainly did on the 126 when they went to alternators. I install them on every older car where they are available.
John

I am going to stick with my relatively new coil as I always carry a working spare and it's just five minutes work to change it.
The beauty of the electronic regulator is that it's also the cheapest!
The drawback now is that I should stay off the road over Christmas.
But tomorrow I'm going to double-check using all the diagnostics.

John jjacob, you were right again (I think). The Bosch coil, which must have been damaged by over-voltage, definitely has a reduced resistance from the value it started with when new. I am running with an original Metz coil and have put the Bosch to one side for now
I have been chasing a cold-start problem for some days now and although things are improved, I am now certain that there must be a better coil to pair with the 123 than the Bosch.
I'm getting a good spark now but it's not setting the world on fire. When it's sub-zero outside or when, as today, there is a a bit of flooding with petrol after messing about, the engine point-blank, will not start.
There must be a coil with sufficient guts, as on modern cars, to force a healthy spark in all conditions.

fiat500 said:

John jjacob, you were right again (I think). The Bosch coil, which must have been damaged by over-voltage, definitely has a reduced resistance from the value it started with when new. I am running with an original Metz coil and have put the Bosch to one side for now
I have been chasing a cold-start problem for some days now and although things are improved, I am now certain that there must be a better coil to pair with the 123 than the Bosch.
I'm getting a good spark now but it's not setting the world on fire. When it's sub-zero outside or when, as today, there is a a bit of flooding with petrol after messing about, the engine point-blank, will not start.
There must be a coil with sufficient guts, as on modern cars, to force a healthy spark in all conditions.

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123 do recommend the Bosch Blue coil with their ignition. It needs to be a coil with a minimum of 3 ohms otherwise firstly it invalidates their warranty and then secondly it affects the ability of circuitry inside the distributor to produce a decent spark. I've read up on it previously and recall somewhere it was stated that a coil that works perfectly ok on a points setup doesn't necessarily work ok with a 123 ignition, any slight degradation of the coil really affects it working efficiently apparently.

If you have damaged the coil by over charging, then the chances are it's just going to deteriorate further with use as you have started off the insulation breakdown on a slippery slope.

Bosch Blue is regarded as a high energy coil, there are others around like Megaspark and Powerspark but the fact that 123 recommend Bosch and I think it is even recommended by AG as well. There are dodgy Bosch Blues out there though, I think the Brazilian ones are meant to be suspect? Do you have a model number on your Bosch coil?

Vitesse said:

There are dodgy Bosch Blues out there though, I think the Brazilian ones are meant to be suspect?

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Thanks for the comprehensive reply Tony. I think I have a good one as the source was excellent. Any badness in it will have been caused by me. Looking at data on some sites it appears that the LT resistance of slightly less than 3 ohms on mine may be normal.
It's like all of these subjects when you get into the detail...there is tons of conflicting technical information and opinion.
I found a web-page that was tring to debunk the idea of the supremacy of that coil, but it was pushing CDI systems, which I think are a whole different thing.
123 suggest the blue coil but my experience both of the company and of the coil is that they are not as good as their hype. Consequently I prefer to find out for myself. I am certain that there must be a way for me to be confident of a punchy, first-time start-up every time.
I'm going to soldier on for a few weeks and see how things go, but it honestly used to start better with points although the static and dynamic timing on the 123 are perfect and do stay that way.
I find that if you take price as a measure of quality, with this supplier the blue Bosch coil is not the best by quite a wide margin. Although I do realise that many of the higher output coils can't be used because of their very low prmary resistance.

http://www.gsparkplug.com/ignition/...1VXfyzIk5CMstGpuUphKTymEsFzy0ZBoC9NDw_wcB&p=1