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Why do coils die?

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T

Tinster

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My TR6 eats coils- always has.
I get about 40 miles and then I have to
replace the coil.

I have less than ten miles on my new Lucas Sport coil
and it appears to be fading fast. It barely got me around the hood this morning.

The usual symptoms are the car slowly loses acceleration
capability. Then the engine begins to stutter and shake.
Then the engine begins to knock like I used low octane fuel
or that I'm in the wrong gear. Then I lose idle and finally
the car dies altogether until a new coil is put in.

Replace the coil and all is well for another few miles.

100% new electrical system in car. Converted to GM
alternator and a Dan Master Power Block entire wire harness

So what makes coils die? Anything in particular I should be
looking for? I alway carry two spare coils in my trunk and
routinely have to change them out.

thanks,

d
 
I think that a Lucas Sports Coil is a coild that does not require an external ballast and that a TR6 would originally take a coil that requires a ballast (specifically a ballast wire). Have you taken this into account?
 
Did you powder coat them? (Thought I saw one in a previous post that looked powder coated).
 
Tinster: I have made a mental note that it seems to
me that owners with modified/upgraded/newer/hotter....
you pick it....ignition systems have seemed to share
same or similar woes. Just something I made a mental
note of from viewing previous threads.

I have been fortunate enough to not have those
experiences. Makes me wonder if it's because I'm
so ignorant of mechanics, that my best defense has
been to simply replace with all OEM parts -- save my
starter, which seemed to be endorsed by friends on
the Forum.

If it is so, then there is bliss in ignorance, I suppose.

I am preparing to duck, cause I'm probably going to be
bombarded by the true mechanic types that I so listen
to and respect....but I just couldn't help but put my two cents in. Sometimes, there's beauty in simplicy. Please
ignore my ramble if it just doesn't apply.
 
Yep,
After reading the articles I previously referenced, it would seem to me that Dale has the coil that is designed to operate at 6 or 9 volts. Operating it at 12v would cause premature failure. The original wires to the coil provided 12 volts at engine start then switched to the resistor wire that drops the voltage for continuous operation. So he should either get a 12v coil or add a ballast resistor.
 
The following information is probably in the links posted above so I'll try and keep my tests below short.

First look at the voltage the coil runs on.
Connect a jumper wire to the coil (-) terminal (the one connected with the white/black wire to the dizzy)
Connect the other end of the jumper wire to chassis ground.
(This insures current is flowing through the coil during your tests... it's a must. The other way to do this is to make sure the points are closed if you don't want to fit the jumper wire).
Get out your volt/ohm meter and set it to measure volts.
Switch on the ignition and measure between coil (+) and chassis ground.
If you measure 12V you have a regular ignition system and need a nominal 3 Ohm (standard) coil.
If you measure 6-9V you have a ballast ignition system and you need a ballast coil.

To see what coil you have, label and remove all the low-tension wires from the coil. Set your volt/ohm meter to ohms and measure across the coil's low tension terminals. A standard coil will measure close to 3 Ohms, a ballast coil will be somewhere from 1.2 to 2 Ohms.

Don't forget to remove the jumper wire from the coil (-) terminal when you're done.
 
With all these stories about burning out a coil, I plan to keep the one that came with my TR3A when I bought bit in 1958.

Once when I spent a few days at Roadster Factory, a TR3A owner drove in for a new Lucas Sports coil. He had replaced his twice already and now this last one was on its way out. He would drive varios trip until he had accumulated about 2000 miles and then the coil would fail. He'd let it cool (along the side of the road or maybe in the middle of a bridge or tunnel) and then it would start again. About 1000 miles later, same thing. Then 500 miles, Then 250 miles and then 125 miles. Each time he would stop and let it cool down, but the next failure was almost predictable. Both his coils had degraded like this.
 

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Hi Dale just guessing, but is it possible that the ignition could be on at all times without showing the light. I remember once hearing about a problem like that and if the points were closed, the circuit would heat up the coil when the engine was not running. Do you even have points?
Sp53
 
Hello Dale,

apart from the suggestions for ensuring you have the correct coil, it is also worth doing a system voltage check with the engine running in case your, albeit new, alternator is giving too much voltage.
(In reply to your question what causes a coil to burn out, one is excessive voltage such as a ballasted coil without the ballast in circuit and the other is too high a duty cycle such as when the ignition is left on and the engine is not running.)

Alec

P.S. I just remembered another, less common cause, the coil clamp being too small or too tight and crushing the can. Triumphs have their coil mounted on the engine, which although I can't remember a coil failure, I don't like (vibration + heat) so I mount mine on the inner wing.
 
Some coils go to heaven, and some pass through the Bermuda Triangle and go to Puerto Rico. It may be that simple... or the other guys may be right.
 
Don Elliott said:
Once when I spent a few days at Roadster Factory, a TR3A owner drove in for a new Lucas Sports coil. He had replaced his twice already and now this last one was on its way out.
Click to expand...
Ken Gillanders once told me of buying an entire case of Lucas Sports coils with the intention of reselling them. He found that nearly 3/4 of them were bad, with a significant number of those having shorted coils (which would lead to rapid failure in use).

For some odd reason, I've never bothered with a Lucas sports coil ...
 
2wrench said:
Makes me wonder if it's because I'm
so ignorant of mechanics, that my best defense has
been to simply replace with all OEM parts
Click to expand...
FWIW (not much), I'm on your side. While I have nothing against modifications, they nearly always involve some level of compromise, which frequently is shorter life.
 
Hi Dale I suppose an easy way to see if your ignition is hot when the key is off would be to either bridge the solenoid or if you have a push button try and start it with the key in the off position. Another way would be to loosen the distributor cap and check for spark. Be careful with this because the condensers/ coil might discharge and give you a one time healthy shock. In addition, I suppose the ducks could all line up in a row so that a condenser ground could be interfering with the coil, but I would think it would misfire.
Sp53
 
If your key has been off for an hour or two and you can't touch the coil because it's too hot, then you know that you always have power to the coil - even with the key in the OFF position. If the coil is cool, that's not where the problem is.
 
As a born experimentalist, I think I would try putting an inline fuse on the LV supply to the coil. Fuses are cheaper than coils :smile:
 
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