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20 Year Mistake - Coil Type

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dklawson

dklawson

Yoda
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20+ years ago I bought an ignition coil from VB for our GT6. Now that I am rebuilding the engine I am cleaning up all such ancillary parts while waiting on the machine shop.

For some reason I decided to measure the resistance across the low tension terminals. Much to my surprise... I measured 1.5 Ohms... not 3 Ohms. I do not have a ballast ignition system so the coil is "wrong". Now I understand why I was going through so many sets of points before switching to electronic ignition. Frankly... I am surprised I didn't fry the electronic ignition!

In the future I guess I'll have to check parts, even new parts, more carefully.
 
I, too, was a late learner... after I had driven my TR3A for 25 years I was perusing a lube chart (slow day I guess) and saw a zerk indicated that I had never noticed before -- the one on the driveshaft slider.

Does make one consider 'What else am I missing?'.
 
The spark that burns brightest also burns shortest...Bet it ran great between points!

John
 
How would one determine which type of coil was proper for a given car? I have wondered this many times over the years,
 
I think that the Vintage Triumph Register may have a listing of which cars used the ballast resistor and all the rest did not. I know they have the quick fix, white wire swap out and that may be part of it.
 
TR4A_IRS said:
How would one determine which type of coil was proper for a given car? I have wondered this many times over the years,
Click to expand...
Turn the engine until the points are closed (or install a jumper from the point terminal of the coil to ground). Turn on the ignition. Measure the voltage across the two low tension terminals on the coil. If you find 11-13 volts, there is no ballast resistor present. If it's around 6-9 volts, there is a ballast present.

Or if it's a Triumph, just ask here :smile:

Note that another way to deal with a "ballast required" coil on a car that didn't have a ballast originally is to simply add a ballast resistor. Any FLAPS should have one. I ordered one from TRF hoping it would look like the original (early Stags used a discrete ballast mounted on the coil); but what I got looked just like the one from my FLAPS. But it seems to work fine and, being larger, probably doesn't get as hot as the Lucas model.
 
TR3driver said:
Or if it's a Triumph, just ask here :smile:
Click to expand...

Then I guess I should ask, what would be correct for a TR4A?

My coil is not original to the car (as you would expect), and the coil I purchased at the time (about 15 years ago) came with an external resister. I ran the car both with, and without, the ballast resister. I couldn't tell any difference, so I just left it off.

Now I am just wondering if the new coil that is in a box on my workbench is the right one to put in when I tune up the TR4A this spring.
 
You've got a lot of company Doug. I'm personally convinced that the bad rap some folks give electronic ignitions like the Pertronix unit is because many folks run the wrong coil.
 
TR4A_IRS said:
TR3driver said:
Or if it's a Triumph, just ask here :smile:
Click to expand...

Then I guess I should ask, what would be correct for a TR4A?

My coil is not original to the car (as you would expect), and the coil I purchased at the time (about 15 years ago) came with an external resister. I ran the car both with, and without, the ballast resister. I couldn't tell any difference, so I just left it off.

Now I am just wondering if the new coil that is in a box on my workbench is the right one to put in when I tune up the TR4A this spring.
Click to expand...

If it came with an external ballast, almost certainly your coil needs one. And a TR4A would not have originally had a ballast wire; it was not introduced until some time during TR6 production.

Leaving it off will shorten point life (sometimes dramatically, I've had them fail in less than 200 miles when the rubbing block melted) and coil life.

Most (not all) coils are marked, with something like "external ballast required". If you can't find a marking, the best thing is to measure the primary resistance (between the two small terminals, with the wires disconnected). If it is around 1.5 ohms, the coil needs an external ballast. Around 3.0 ohms indicates a coil that doesn't need a ballast. Less than 1.2 ohms or so indicates it is a non-point coil, designed to be used with some sort of "high energy" electronic ignition. And more than 3.3 or so indicates a bad coil.

Note that many ohmmeters (or multimeters) don't read exactly zero even when the leads are shorted together. To get a meaningful reading of such low values, start by shorting the leads together and noting what the meter reads. Then subtract that from your measurement. For example, if the reading with the leads shorted is 0.7 ohms; and you read 2.4 ohms on the coil, then the real coil resistance is closer to (2.4 - 0.7) or 1.7 ohms (indicating a coil that needs an external ballast).
 
tdskip said:
I'm personally convinced that the bad rap some folks give electronic ignitions like the Pertronix unit is because many folks run the wrong coil.
Click to expand...

Could be; but the Pertronix I got would simply not work on battery voltage that was plenty with points. Root cause was a bad battery, but it was still putting out enough for the starter to crank the engine relatively rapidly, the Pertronix just wouldn't fire the coil. Switched back to points and it fired right up, first time, every time.

Until several months later, when the battery finally finished dying.
 
Lots of good information guys. I think I have been sking the wrong question.

What should be in a TR4A?

I can determine what I have, based on all the info in this post, but what is supposed to be in there?

I am wondering if the PO put the wrong coil in and I have just been replacing in kind.

BTW, I have a Lucas Sport coil (LUDLB105B)on the shelf, waiting to go in when the car gets her tune up. I am also using a pertronix, and have been for about five years.
 
Sorry, Ian, I meant to answer that but I see I was not clear. A TR4A originally had no ballast and a 3 ohm coil. Your DLB105B should work fine. (Although the one I got at the 2009 Triumphest has already died.)

I also neglected to mention that Pertronix recommends using their 1.5 ohm coil without a ballast, on V8 engines.
 
Related to this:

I'm running my 1.5 ohm coil through a ballast resistor <span style="text-decoration: underline">all the time</span>: even during starting.
In other words, I don't have a bypass circuit to allow 12V for starting.
This is on my race car.
Using a "Standard" (brand) coil...not a Pertronix coil.

I've been running the same Pertronix on my race car for almost 10 years with this setup and no issues.

My theory is that this is an "electrical cushion" and reduces "spikes" through the Pertronix.
 
I have ordered a Bosch Blue from Jeff at Advanced Distributors. I like Bosch and this is the "correct" resistance for the wiring in our GT6.

Randall has given all the information I would have posted on how to measure the coil and the coil wiring to determine what you have and what you need.

Nial, I considered buying just the ballast resistor and continuing to use the "incorrect" coil I bought from VB so long ago. However, it occured to me that the coil (marked VW on the bottom and Yugoslavia on the top) may have been for an electronic ignition. Those coils can be quite different and not happy with points. So... I went for the Blue.

(As an anecdotal example of coil mismatch... the European Minis built with factory electronic ignitions use a special low resistance coil that appears to be a ballast type coil... but isn't really. If you use a ballast coil on their electronic ignitions it will fail. If you use the electronic ignition coil on a car with points... other problems surface. I am simply not convinced the old VB coil is something I will ever want to use.)
 
TR3driver said:
Sorry, Ian, I meant to answer that but I see I was not clear. A TR4A originally had no ballast and a 3 ohm coil. Your DLB105B should work fine. (Although the one I got at the 2009 Triumphest has already died.)

I also neglected to mention that Pertronix recommends using their 1.5 ohm coil without a ballast, on V8 engines.
Click to expand...

Thanks Randall. I can see clearly now...
 
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