Much experience has led me to : always regard coil and condenser as a pair (was told this by a Lucas Competitions dept man), a coil failure can damage the condenser and viceversa, and seek out quality: Lucas stuff and unbranded is largely asian repro. Buy Bosch, 6 and 12v still available, from a reputable supplier, eg. Bosch centres, and condensers from Nick Swift at Swiftune Racing who are A series engine builders. Dissapointingly expensive at the outset, worth it in the long run. Winston

As you know Brian, I've had no problems with my 1934 coils,
but there will come a day when we're on a run together and .......
will I borrow one of yours
or you one of mine...
.
I recall a few years ago in Brittany I had a similar problem, only to find the cam follower to the dizzy points had worn down... That was a new'ish set too, replaced those with one of my originals, still going strong.
.
Honestly, you have my sympathy.

Location: On the edge of Europe - West, and west of Brian..

Hi Brian,
The only times I have experienced coils overheating in normal running is when the points have closed up to an extent, thereby giving a longer dwell angle (i.e. causing the points to remain closed for a greater percentage of the ignition cycle).
If you have a lot of play in the distributor centre spindle this can give this effect at normal driving revs, even if the point gap looks OK when static.
If you have access to a decent dwell meter check your dwell angle at tickover and then see if it increases when you rev the engine.
I believe with a standard Lucas DJ4 dizzie the dwell angle should be 45°. Other distributors will be different.

Ian Mc.

Location: Shropshire

Not really relevant but may be of interest.

A local Bradford owner had been complaining of endless points trouble.
The vehicle had a switch in place of a key and at a recent local car show the engine was stalled and not turned off. Later whilst several were surveying the engine the coil exploded and covered all with hot oil!.
A 6v coil on 12 volt. (Some coils intended for use with ballast resistor are marked 12v but really 6v)

Bob Culver

Location: Auckland

Such a fault almost defies diagnosis ! A batch of faulty/substandard coils from the same supplier seems most unlikely. But I would have thought that all the suggestions would result in poor ignition performance which surely Brian would have noticed. Whatever wear/breakdown is suspected, the outcome will have been seen before. For three coils to fail in quick succession after so many other components have been changed may be unique.

I hope you get it solved Brian and do revisit the thread to tell what caused it.

After thought edit: last weekend, chatting to fellow Austineers I heard about a problem of connecting the primary coil connectors the wrong way around. Especially I think if they are marked + & - rather than CB and SW. Didn't hear what the likely outcome would be but was told the issue is discussed on the Dorset (?) website, but I can't find it there. It's even possible, with items originating from China that the marks are incorrect anyway..may be a red herring.

Over the years I have worked on literally thousands of broken-down cars with an ignition problem, and many were in the days before electronics. Coils hardly ever fail, but they do sometimes. Good quality genuine coils are much better than cheaper brands. Leave the ignition on by mistake with the points closed and a Lucas coil will not burn out, Intermotor coils burn out easily.
I've come across many ballast-system coils with the ballast resistor missing (often by fitting the coil to the wrong car)and this rarely bothers the coil. With the lower resistance coil usually the car stops because of problems with the points - either burnt or the plastic heal melted.
I found there are 3 ways a coil can fail...
1. Windings can burn out. Very rare, especially on a good brand.
2. An internal wire can break. Caused by vibration. Very rare, but does happen when coil is bolted to engine.
3. A crack in the coil 'neck'. This means the coil is working - it is creating the 20,000 volts - but that voltage short circuits to earth through the crack.

I have NEVER found another fault to cause failure of a good brand of coil, and never found coil and/or condensor faults to be inter-related.

Hope this helps.

Location: United Kingdom

I seem to remember we have had a few correspondents who accidently left the ignition on and damaged the coil- don't remember if Lucas or chinese.

"Intermotor coils burn out easily."

What are Intermotor coils?

Tony.

Location: Malvern, Melbourne, Australia

It's a make of coil:

R,

Thanks- I haven't looked at electronic ignition so haven't seen them before.

Tony.

Location: Malvern, Melbourne, Australia

They make all sorts of coils and other components (that was the first pic that came up), it's just a brand name.

I can't make out what coil manufacturers our cherished suppliers come up with, are they pukka Lucas ones or foreign ones?

Location: Just East of Sandy

Interesting- just searched a couple of big Melbourne Auto Spares suppliers and found no mention of Intermotor.

Tony.

Location: Malvern, Melbourne, Australia

I just did the same with Vegemite over here, similarly dissapionting...

Intermotor in the UK and Europe, they also appear to have a presence in the USA.

http://www.intermotor.co.uk/smpeurope/intermotor.asp

http://www.smpeurope.com/smpeurope/catalogue.asp

Jeff.

Location: Almost but not quite, the far North East of England

R,

At least you have Marmite which is almost as good!

Jeff,

"Intermotor in the UK and Europe, they also appear to have a presence in the USA."

They seem to be known here but not stocked by the larger auto suppliers.

Tony.

Location: Malvern, Melbourne, Australia

Have now got yet another coil from one of our cherished suppliers, I wonder how long this one will last. One suggestion that has been made to me was that the dynamo maybe charging too high. It has been up to 10 amps for a while, would that have made any difference? I have knocked it back a notch or two to see if the problem reoccurs. What do other forum members think?

Location: Just East of Sandy

If the battery is intermittently connected to the dynamo due to some poor connection or earth the system voltage will rise way above 6v. I have had this on other cars which nevertheless started, but burned out bulbs, not the coil!

If this problem had related to 12v would suspect a ballast coil or 6v coil or a 12v low resistance coil intended for electronic ignition. Is it just possible that a batch of low resistance coils have been made for use with electronic ignition kits and escaped onto the general replacement market? As above points trouble would usually soon indicate the problem if the high ammeter discharge with engine not running is not noticed.

Bob Culver

Location: Auckland

10 amps from an Austin Seven dynamo - WOW!

Tony.

Location: Malvern, Melbourne, Australia

Hi Tony

The heating effect increases as the square of the current, so, even though the full armature current includes also the field and ignition current, 10 amps is vastly more severe than 8 Nevertheless 10 amps at 6v is reasonable if not too sustained for the DEL and subsequent Lucas dynamos. 8amp on the meter is recommended which more or less balanced the original light load, but many match a higher load without immediately melting all the commutator solder.
A defective battery can also cause system voltage to soar, but would normally show as poor cranking.

Bob Culver

Location: Auckland

Not directly connected with Brian's problem I wonder if anyone can say what the resistance of a genuine original Austin 7, 6 volt coil is ? An indication of the ignition current without the engine running would be a guide.

I ask because some 6v coils advertised as 6 volt are actually 12v coils intended for use with a ballast resistor of 1.5 ohms. The resistance of the coils is also 1.5 ohms in my limited experience..

I'm wondering if a proper 6 volt Lucas coil might be better than a black no-name one.

Location: A little East of Sandy

Roger, my Lucas original 1937 6V coil measures 1.5Ω . As might be expected, unless Ohm's Law is incorrect, with the points closed, ignition turned on but engine not running the current passed is approx. 4 amps.

As the prewar Lucas symetrical cam (usual in DS4, DJ4 and DK4 distributors)with the points correctly gapped gives an approx. 50% duty cycle (45º dwell angle), the average current taken by the coil with the engine running is 2A.

If you have a later, different, dizzie these usually have a fast opening, fast closing cam which has a dwell angle of around 60º (66% duty cycle) and will have the effect of delivering a coil average running current of approx 2.7A

Ian Mc.

Location: Shropshire

Thanks for that specific and helpful info Ian. Any worries I had on that account are not justified then - as long as the coil itself is of good manufacture..

Location: A little East of Sandy

Can you still get a Lucas coil and if so, from where?

Location: Just East of Sandy

Apparently from HERE, Brian. At least he says so! I assume we are talking 6 volt? Lucas 12v coils are readily available still.


Ian Mc.

Location: Shropshire

or a lot cheaper here...hopefully they are genuine !

http://www.gsparkplug.com/shop/ignition-coils.html?limit=all&mode=list

Location: A little East of Sandy

I don't believe that Mr Green would say that they were Lucas if they weren't, Roger.
However, how todays "Lucas" (made God knows where - most Bosch stuff is now made in Brazil and elsewhere outside of Germany) compares with Lucas of the 30s, I don't know.
Read about"Lucas" today HERE

Be aware that both the Lucas DLB102 and DLB110 are actually designed for use on a 12v system with a 1.6 ohm ballast resistor. However, the primary coil resistance is 1.5 ohms and I can think of no reason why they wouldn't give satisfactory service, unballasted, on a 6 volt system.

Ian Mc.

Location: Shropshire

In our spares old stock I found an original German Bosch 6 volt (VW) coil for the Latrobe - might still be some out there.
But as Ian notes most are now made goodness knows where and under what quality control. I fitted the Chummy with an eBay unbranded 6 volt 'screw in top' coil - so far so good (just don't leave the ignition on - I always disconnect the battery as well)

Tony.

Tenth try with two complete new entries

Location: Malvern, Melbourne, Australia

Brian, is the coil connected correctly for the polarity of the vehicle? The points earth the coil so if you're negative earth, minus on the coil goes to the distributor and vice versa for positive earth.

Peter

Location: Lincoln

Yes, Peter, all the connections are as they should be.

Location: Just East of Sandy

Just to update on the coil situation. I had some time on my hands over the New Year - quite a rarity really - and having returned from a shortish (5 mile) run and letting the car idle a bit while opening the garage, the engine stopped and failed to restart. The coil being quite hot to the touch. Just a thought, change to a brand new coil, which I did, and sure enough it restarted no problem. After settling the car into the garage I experimented by switching back to the now cold original and it started perfectly. I then went to a coil which "failed" on me back in September and it started the car perfectly too. So in short the coils get overheated in some way and are not again usable until cold. Dynamo has been adjusted already to reduce to 6 amps instead of the higher figure, and the points, adjusted correctly and the condenser have already been replaced with new. Why should all my coils overheat ?

Location: East of Sandy

I would look at your battery leads.
My thoughts are as follows:-
The Seven controls the voltage in the electrical system by the voltage of the battery, the dynamo produces volts in relation to the speed of the dynamo which is why the same dynamo can be used in a 12v system without any modification.

If you have high resistance at either of the battery terminals ( or the earth to the body ) then the voltage at the dynamo / cutout could be higher than 6v in your 6v system which in turn could be cooking the coil. The voltage at the battery would be lower due to the resistance in the leads.

Just a thought !

Malcolm

Location: Falmouth

I would check your ignition circuit to see if current is passing through the coil with the ignition turned off.
Alternatively, wire up an external temporary circuit to the coil and see if the coil still gets hot.
As the coils seem to recover perhaps it is the wiring that is heating up at a high resistancce point and that is going open circuit and thus switching off the ignition. It is odd that three coils seem to be behaving in a similar manner.

Bryan

Location: Not quite as far west as Sandy

I agree with Malcolm. The only reasons for your coils to overheat are either too high an operating current, or the correct operating current but for too long a time period.

Causes of the first can only occur if too high a voltage is applied to the coil primary terminals. Suspects, as Malcolm suggests, are resistance in the battery leads/ connections. Remember that the coil gets it's earth side supply directly from the dynamo body (via the points in the dizzie). The battery earth side is normally connected to the dynamo only via the engine mounting bolts, chassis, bodywork etc. Do you have a heavy duty earth connection directly between the battery earth terminal and the crankcase?? If not you should install one, as I have done (heavy guage cable from the battery terminal direct to an appropriate lug under one of the gearbox top securing nuts); relying on chassis return is not a good idea, any stray resistance in this path will result in the voltage applied to the coil being higher than the battery voltage at normal driving engine revs.

Cause of the second is too high a dwell time of the points closed, as I covered in an earlier post on this thread.

Ian Mc.

Location: Shropshire

I have had the same problem with coils. 3 brand new ones failed within 100 miles.
I cured the problem by fitting a old original (1962) Lucas coil.
If you shake a modern coil the oil inside sounds very thin, the old coils seem to be heavier with thick oil.
I am convinced that the modern coils get overheated due to the difference in their manufacturing quality.

Location: Chichester

I don't know how old the 6v coil is on my car but it has worked O.K. (touch wood) for many years.

Location: Derby

I had this problem with a RR20 years ago. The cause was too large a gap between the rotor arm and the cap segments! Worth checking.
Dave

Location: Bonnie Galloway

Gonna start by putting a cable from the earth terminal on the battery direct to the engine. Starter fixing bolt okay?? Will keep everyone informed.

Location: East of Sandy

Location: Shropshire

Location: West of just about everybody, last place the sun sets !!

To update everyone. Went on a run with the CA7C two weeks ago and the coil overheated after 25 miles - red hot to the touch. Have made now a separate earth cable from the earth of battery direct to starter fixing bolt. After starting the car and letting it warm up for the radiator to get hot all the way down, the coil is starting to get warm; should it run warm at this stage?

Location: East of Sandy

Hi Brian, all down to definition of warm, I suppose, but I would expect it to be noticably warmer than the bulkhead - without being decidedly hot. In my experience, even after a long run it should never feel hotter than, say, a mug of coffee which was 5 to 10 minutes old.

Ian Mc.

Location: Shropshire

Have you tried a old coil yet ?. I would recommend a Lucas one from the 1960s.
It cured the problem you have for me..
Martin

Location: Chichester

Not yet Martin, I am trying to isolate the problem by doing one suggested remedy at a time.

Location: East of Sandy

As part of routine maintenance I notice the CB points gap is mighty wide - around 20 thou. What effect would this have on the coil's performance?

Location: East of Sandy

That would reduce the dwell angle, i.e. the points would open sooner and close later so the coil would have a shorter duty cycle and therefore run cooler.

Ian Mc.

Location: Shropshire

Bu**er, it wouldn't be that then. May put an old coil on at the weekend and see if that helps - snow permitting!

Location: East of Sandy

Hello Brian,
I'm pleased you might try a old coil. For the first 35 years working as a mechanic I never replaced a coil ( they just did not fail ) however in the last 5 years I have replaced 7, the last one was on a morris 1000 it is positioned on top of the dynamo next to the engine block therefore it overheats even quicker.
Martin

Location: Chichester

One factor could be plug gaps; Austin always recommended 0.018" to 0.020" for sevens in period but I wouldn't be surprised if today most people set them to 0.025" or even greater.

Ian Mc.

Location: Shropshire