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MG Midget and Sprite Technical - Replacement for points ignition?

I have a 1976 1500 midget, I am looking to replace the points etc on my distributor with an aldon ignitor system. I would also like to replace the coil too, but after looking through the archives I am none the wiser as to what type of coil would be compatible.
Can anyone suggest a suitable coil to go with the ignitor, I assume it needs to be a ballsted coil?

Thanks for your help

Kevin
K Grice

Keven. There is no need for any special coil when using any of the electronic points replacement systems that I am aware of. Many companies take the opportunity to sell "special" coils, figuring that if someone has decided to spend the money for a points replacement system, perhaps they will spend a bit more money for an "uprated" coil. Most of the time, the coil is never required to produce the "uprated" voltages--and a coil only produces a voltage output sufficient to cause the spark plug to fire. Thus, your "40 Thousand Volt!! Super Chicken Pluck!! Coil" is, most commonly, operating at about 11K volts, rarely getting up to 18K under difficult conditions. This is within the range of the standard coils which provide up to 20K volts.

If you want to spend the extra money to get a coil that screams "SUPER COIL" at everyone who looks at it, that is a personal decision. But it is not needed, and, were it used at its maximum potential voltage (generally 40K volts), your rotor, dizzy cap, and the spark plug leads would deteriorate at a much faster rate than under normal circumstances. To take advantage of a Super Coil, you also need Super Leads (available from the same manufacturer and in the same colors) and the Super Rotor and Super Distributor Cap.

Marketing ploy and not needed for must use.

Les
Les Bengtson

Simple answer, contact Aldon direct. They will give you all the info you need.
Cheers John
JOHN HALL & JULIE ROBERTS

John. Maybe. Depends on what they are trying to sell. Most of the companies offering "electronic points replacement" systems will offer to sell you an "upgraded coil" to go with it. I have an old Sun Engine Analyzer which allows me to test out engines while not on the road. I have cross checked my results with the assistance of a friend, a professional mechanic who owns his own shop. Hr has a portable engine analyzer, a fraction of the size of mine, which allows us to test the results I have determined against what is happening when we are driving on the street. With my 79 B, having the 40K volt Lucas Sports Coil, we have never been able to get a reading above 18K volts--well within the capacity of the factory 20K volt coil.

I have been doing this stuff for a long time. I have sufficient academic background to understand what research is all about. I have had sufficient funds to purchase engine analyzers and distributor test machines, of the older models. I have friends who work as mechanics and who have the most modern versions of such machines.

All of this has lead me to question some of the beliefs that I held when I was younger. I used to fit the Lucas Sports Coil because it "gave a hotter spark". It does not, under the majority of conditions. When it does, it requires a distribution system of the highest grade and in the very best of condition. A "high voltage" coil, with older coil lead and spark plug wires, simply grounds out more quickly than a coil that develops lower voltage. Any dirt, or moisture, on the spark plug allows the higher voltage to go to ground through the moisture/dirt, rather than through the spark plug.

All of this needs to be figured in. Yes, many of the factory race/rally cars used the Lucas Sports Coil. But, an engine tuned before one race/rally, and retuned after that race/rally, is quite different that what most of us use these cars for. Even then, there was no documented evidence, available on four shelves of books, which indicate that any actual tests had been performed to demonstrate the effectiveness of the "high voltage coil" as compared to the standard, factory coil.

Les
Les Bengtson

Agree with Les - the size (voltage) of the spark depends on the plug gap...

A
Anthony

Well the spark voltage IS dependent on the plug gap but there are a number of issues that also need to be considered.

Could a standard coil drive a 30/32 mm plug gap?

Is a wider plug gap a good thing?

The quality of the spark is not only due to the voltage but is also dependent upon energy from the coil, hence the term "high energy coils"!

Simply measuring the voltage of the spark is not I believe the only measure needed to establish whether it is or is not better.

I can only say that in tests I have done on rolling roads I found that with the High Energy coils I found that reducing the plug gap to 30 thou did increase HP and 30 thou was the optimum when max power was at 7K RPM. Unfortunately I never did this test with a standard coil so I am unable to advise on a direct comparison, which is a shame.
Bob (robert) Midget Turbo

Yes I did mean reducing to 30 thou, because I had started at 34 thou.
Bob (robert) Midget Turbo

The only problem I have with your research, Les, is that you apparently ASSUMED that the stock coil would actually perform at the rated voltage although you already KNEW that the aftermarket one did not. I would really like to see back to back results of the "20,000 volt" coil and the "40,000 volt" coil. It is quite possible that the posted voltage is determined through some arcane process that has nothing to do with real-world applications such that the "40,000 volt" unit really only produces 18,000 volts and the "20,000 volt" unit only produces 8,500 volts. In that case, I would still want the "40,000 volt" unit in my car.
David "wish I had room for one of those Sun machines, but I would probably just put another Spridget there if I did..." Lieb
David Lieb

David. No, I did not assume anything. Just did not want to go on too long in my post. There is a method to check the maximum voltage a coil can put out and read that voltage on the screen of the engine analyzer. Basically, you simply pull the spark plug wire terminal off one of the spark plugs and hold it some distance from the spark plug terminal. As you move backwards (away from the spark plug terminal), you watch the voltage required to spark the plug go up. I performed this test using the Lucas Sports Coil, the standard 12V coil off my 68GT and the standard "6V" coil off my 79. All of the standard coils were capable of putting out 20K volts and the Sports Coil is capable of putting out 40K volts, just as the factory specifications indicate. But, I have never had to put out more than 18K volts under any road driving conditions. Have not been able to get my mechanic friend to hook up his laptop machine and go out to the race track with me, so I do not know if, under those conditions, we would have a requirement that a standard coil could not meet. But, accelerating onto a limited access highway, and running the speed up to 80 mph, does not produce a requirement that the standard coil cannot meet.

Robert. What fuel were you using? I am not seeing any different voltage between a spark plug gap of .030" and .035", at least that is noticeable on my machine. But, this is using our blended fuels and I do not have access to a rolling road and someone familiar with British cars to help me do my tuning. Thus, I depend on people such as yourself for guidance. Your thoughts would be appreciated.

Les
Les Bengtson

Once you go beyond 30 thou plug gap, the extra volts begin to stress the rest of the system (rotor arms in my experience!) such that they fail much more quickly. So IMO there's not point in a 'special' coil that is able to provide volts that the rest of the system - rotor arm, distib cap etc. - cannot withstand.

At 35-40 thou, I was going through several rotor arms per year. This is not an expensive failure, but more one of inconvenience, e.g. they went:

- 3 miles from a friend's house near Halifax
- on the M50, after a solo drive back from LeMans
- on the M5 on the way up to doing my KSeries conversion

(i.e. never in the garage with 30 mins warning!!)

A
Anthony

But Les, we COUNT on you for those long exhaustive posts. Thank you for the clarification.

Why do our British ignition parts erode and die with a mere 0.035" gap? 0.035" was the spec on most Chevies until the HEI ignition came out in the mid-70's and it was common practice to toss in an Accel coil and open the gap to 0.050" with no issues on standard ignition parts?
David "how about with the Bisch caps and rotor on the 123/Mini distributors?" Lieb
David Lieb

coilpack ! just a thought :-)
darren 1800 fogeye

Just to add a little extra. For years I have run 28 thou plug gaps. I have now upped the gap to 35/36 thou and have gained 2 bhp on most of our engines. Is this due to fuel change? When race cars are running well I have a little play with settings such as plug gaps and tappet clearances to see if very slight changes make a difference. Hard working Bs tend to like tightside inlet tappets and loose exhaust tappets. A series seem to respond the same.

We tend to use Aldon Igniters and standard/gold coils in Race cars and 123 dizzies and standard/gold coils in Road cars. We run 12v unballasted coils.

Peter
peter burgess

Well that is interesting, from what Ant has experienced it would seem that the suggestions we mulled over on the other thread do have some credence.
I like Peter have not run with a plug gap above 30thou even with the gold coil so perhaps that is why I have not had problems with rotor arms.
From the experiences of others here it would seem that the higher voltages required to drive a 34+ plug gap could indeed be responsible for rotorarm failures.

Peter I do hope you will monitor the situation with rotor arm failures on the engines you are looking after with 34/35 plug gaps
Bob (robert) Midget Turbo

I will keep an eye on matters. Failure seems random to me and I assumed it was poor quality of replacement parts becoming conductive when hot.

Peter
peter burgess

Peter. I have been running .035" spark plug gaps, on four cars, for over eight years now. The only failure that I have had was with one new Lucas distributor cap which had the carbon bush self destruct. I never have had a problem with a rotor. Mixed bag of Lucas and after market rotors and caps, points type distributors tuned every year before emissions testing. Mostly using the Lucas 45D4 distributors now, but ran the 25D4 on my GT for six years without a problem.

I know there must be a problem because so many people have reported it. But, I wonder if the problem is bad rotors or whether the rotors going bad is a symptom of some other problem which has not been diagnosed?

Les
Les Bengtson

Hi Les

I hope you are fit and well? The problem seems to be faulty rotor arms shorting out when hot.

Peter
peter burgess

This thread was discussed between 21/03/2008 and 25/03/2008

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