coils keep packing up

[picky]

Im having a recurring problem with the ignition coil, The car will run for a month or so and then stop, fitting a new coil solves the problem but I cant keep buying new coils all the time! As I have an alternator fitted the coil is attached to the bulkhead with the terminals pointing downwards, Im using the lucas performance coil. had a spare coil which is a bosch one and it blew a 10 amp fuse when I wired it up, (I have a fuse added in the ignition circuit.)

Help much appreciated,
Picky

[chrisd87]

I also have an alternator conversion and have mounted the coil on the inner wing, with the terminals pointing upwards. No problems in 18 months or so, although I thought it had packed up a few weeks ago it in fact hadn't.

[Willie]

There is a theory that the modern coils do not have as much cooling oil in
them as did the originals. If this is so then mounting the coil upside down
would expose a large area of the windings to air so it would be worth mounting the coil upright. That is assuming that you have fitted the correct
12v type coils and not the 'ballast' types.

[picky]

well i have several blown coils in stock so I could buy a new coil and fill it to the brim with oil from the others. I will try mounting it with the terminals pointing up and see how it goes. Has anyone else had an issue with the lucas performance coils??

[alex_holden]

You probably want to leave some air gap in there otherwise when it heats up the oil will expand but won't have anywhere to go.

[Packedup]

the coil is attached to the bulkhead with the terminals pointing downwards,

That's novel.

As others have said, I'd attempt fitting it the more usual way - Sometimes being different doesn't equal being better...

[picky]

Sometimes being different doesn't equal being better...

I never suggested my way was better. When I fitted an alternator and had to move the coil, I was not aware that there was a "wrong" way round.

[Packedup]

I can't remember ever seeing any car where the coil wasn't horizontal or upright. Which kind of suggests that's the way things are desinged to work.

Besides, isn't it easier to wire it up upright, instead of either having to remember the terminals or do it from underneath?

[chrisd87]

I can't remember ever seeing any car where the coil wasn't horizontal or upright

When I was looking at buying an old landy the coil was mounted on the bulkhead pointing diagonally downwards. Not sure if it was supposed to be like this but it seemed to work ok.

[Nigel2]

It is definitely the 'oil thing', undo the screw in the centre of the HT feed out and top up with oil for horizontle (or other) style of mounting. Why they have reduced the fill on coils I don't know - cost cutting? The oil has changed over the years as well from the pcb toxic type oil to what I think is a standard mineral type. Perhaps there's a chemist out there that can clarify the situation. Sports coils seem more prone to the problem but a standard coil should give enough 'oomph' anyway providing it is getting a good 12 volts+ to it. Worth checking as often there is only around 11 due to corroded connectors and switch contacts.
Nigel

[rayofleamington]

Personally I'd try a working coil from a 40 year old Minor.
I've filled coils all the way with no air and they were ok - even in Africa, however maybe that isn't ideal (or maybe it is fine - hard to say)

[johncannon]

I have blown two sports coils now -last one lasted 6 months. I fitted them as standard on top of dynamo, but am planning to fit my new one vertically. I am confused -what oil should i use o top it up with?

[ben739]

i had same problem on and had to fit mine to inner bulkhead facing upwards, and now no problems. (touch woody)

[pauln]

Having the coil mounted in it's engine mount position on my 1300 caused 2 coils to run very hot and then fail. Fitting the new one on the bulkhead has allowed it to run much cooler. No failure so far.

[washer-bottle]

I have had no end of problems with overheating coils and I have tried sports coils, new standard coils and old coils etc. Things have been better for a while now that I have moved it to the inner wing, but I cant say for sure that I have fixed it yet. When you pick up a coil give it a shake – that will tell you if its full of oil.

Originally I thought it was the (magnetic chopper / hall effect sensor type) electronic ignition and 30 thou gaps so I have gone back to 25 thou and good old points for now. The electronic ignition had a dwell angle of 70 degrees compared to the standard 60 degrees - i.e. primary current flowing for roughly 10% longer.

Then I thought it was because the rotor arm was flashing over. (Test for this easily in the dark with the distributor cap off and the king lead from the coil held carefully near the rotor arm top. If you get a spark on turnover then you have an insulation breakdown in the rotor arm straight through the rotor arm down to the distributor shaft).

My latest theory is that I may also have a problem with my old Metro Lucas alternator giving a spiky output at speed.

The Lucas 25D4 distributor should have a dwell angle of 60 degrees ± 3 degrees with the points gap set to 15 thou ± 1 thou (i.e. a 14 thou feeler gauge should be loose and a 16 thou one tight). The plug gaps should be 25 thou (or 22 thou if you only do short journeys and they foul up).

Check the resistance of all your HT leads are similar, there is no soot inside the distributor cap and that the plug gaps are OK and not sooted up. What plugs are you using and do the gaps look clean?

Currently I have 2 coils both mounted vertically, the main one mounted on the offside inner wing and a spare one hung on the alternator mounting bracket (taken from an old Mini). I have found this works well and its a quick changeover should it start to misfire. When the coil overheats you can not touch it for long, a working coil just gets warm.

Things haven't been helped by a bad batch of pattern rotor arms out there. A standard 12V coil normally has a primary resistance of about 3 Ohms or more. A ballasted coil or an electronic coil will be less (e.g. 1.5 Ohms).

The old Series Land Rover coils are correctly mounted upside down - keeps the water off. Original MM coils (stamped Lucas LA12 on the flat end) are normally pretty tough and give 17kV and are the ones to go for, but watch out if the clamp has been over tightened and the case crushed. The dynamo horizontally mounted coils were cooled by the fan blade. The bulkhead mounted coils are mounted vertically to keep the windings covered in oil and use the bulkhead as a heat sink.
Lucas Sports coils (DLB105) are rated up to 28kV and are recommended for higher revving or higher compression engines where its harder to start the spark. The voltage you get across a spark plug gap is dependant on the spark gap not the coil - a high performance coil just allows more energy ie a fatter spark (more current across the gap) for a longer time. What I mean is that fitting a sports coil when it's not needed might not help matters.

Ballast resistor coils are generally fitted to cars that are difficult to turn over - they run on 12V with no ballast resistor whilst the starter motor is taking down the battery volts and then switch to 9V (by dropping 3V across the ballast resistor which gets hot) when the engine fires. Leaving the 12V connected on a ballast coil will burn out the points and overheat the coil. Other coils with low impedance are designed for high revving engines with more than 4 cylinders where the current doesn't have as long to build up in the primary (low dwell angle). Electronic coils are designed for ignition systems without points (no burn out to worry about) and have a very high primary current (low resistance). Just because one fits an expensive aftermarket no points type electronic ignition type kit doesn’t mean that the electronic switch will cope with switching the primary current of an electronic coil - read the manufacturer's manual.

Make sure that the connections on the primary side are correct - SW means ignition switch i.e. the (negative) supply and CB means contact breaker (i.e. the positive earth). More modern coils assume negative earth and have "+" for ignition supply and "-" for distributor. They will work both ways round, but only one way is correct as the primary and secondary windings are connected together on the "-" or CB connection (i.e. unlike a standard transformer). I am not sure what the best advice is if you have an old positive earth coil (SW/CB) fitted to a negative earth Minor, but I would not reverse the primary connections.

The other thing to watch for is leaving the ignition on with the engine not running as this can just heat up the coil (red light will be on on the dash).

There is a lot of folklore spoken about coils, but I am always willing to learn and spread some more. The old wisdom is that what flows in Lucas wiring is not Amps, but white smoke and heat!

Al

[Kevin]

I have had no end of problems with overheating coils and I have tried sports coils, new standard coils and old coils etc.

Hi Washer just one thing are you running a standard engine or modified as the problems seem to be more common with modified cars, which is a bit of a puzzle when you consider whats squeezed under a mini`s bonnet.

[washer-bottle]

Hello Kevin
My Morris traveller engine is a 1098 traveller that has been modified to 9.5:1 CR +60 thou rebore, 12G295 head, Kent 256 cam, HIF38 SU, LCB exhaust, rimflow valves. I wanted to see what could be done with a 1098. It was pictured in the gym on page 30 in MM Jan/Feb 2006.
Al
PS Is Hitchin in Herts and is it true that they have black squirrels there? Need to settle a quiz.

[Kevin]

PS Is Hitchin in Herts and is it true that they have black squirrels there? Need to settle a quiz.

Yes Hitchin is in the middle of Herts, but black squirrels thats a new one on me I though they were only Red or Grey but it appears you are correct.
http://www.camptonandchicksands.org.uk/squirrel.htm

[MikeNash]

Don't know if this helps, but if you're stuck with a low resistance coil (and so suffering from the hotness) try putting a resistance in series with it. I used an old headlamp bulb with wires soldered to its base plus croc-clips to limit the current. As with most of my temporary lash-ups it lasted for over 10k miles before I fixed it. Got a nice pool of light under the front at night too. Regards, MikeN.