C1 Coil "blown" twice

[Joseph U.]

I have just blown the second Ignition Coil on my 1960 corvette.
When the first one went it burned the ignitioin wiring and was associated with a incorrectly wired ballast resistor. (who knows what caused what but I think that was related to a wire that was rubbing and shorted thru and shorted out to the ignition shielding - but who knows.) That was all repaired and car ran just fine - car died this weekend and the replaced coil is now cracked. The question is "just bad luck or something causing the problem?"
Any ideas would be most appreciated. What causes an ignition coil to fail?
Joe

[John P.]

Re: C1 Coil "blown" twice

Hello Joseph, Five things come to mind. First, make sure you are using the correct coil or replacement coil for your application. Second, make sure you have the correct ballast resistor, and are getting the correct reduced power to the coil positive post when the engine is running. Third, take a volt drop test and make sure you have a good ground on both the engine, distributor, and chassis. Fourth, check your charging system and make sure the system is not overcharging. And last. make sure the wire from the coil to the points is not pulling apart inside or grounding on the distributor housing, install new points and condenser at this time to eliminate any damage to these parts that may have resulted from the improper wiring issue. Good luck, John

[Joseph U.]

Re: C1 Coil "blown" twice

Thanks John,
Couple of questions:
1. Coil and Ballast resistor came from either Corvette Central (Coil) and Ecklers (ballast resistor) so I have to assume they are correct
2. Replaced Points and condensor
3. How do I do a voltage drop test?
4. How do I check for reduced power to the coil
5. How do I check for overcharging?
Obviously I am at a lost here - maybe I need a mechanic.
Thanks,
joe

[Duke W.]

Re: C1 Coil "blown" twice

Never assume anything you buy from a Corvette parts vendor is "correct". They may look correct, but may be functionally very different. All C1 Corvettes had a 0.3 ohm ballast, and you can find coil resistance the the shop manuals. So you need a good ohmmeter to measure ballast and primary coil, resistance, which should be around 1.5 ohms. Do the resistance measurments with the engine off. Then with the engine running and fully warmed up measure voltage drop across both the ballast and coil. Also measure voltage across the battery to verify that the regulator is not overcharging. The correct range is 13.5 to 14.5 volts.

These early low resistance ballast setups had a habit of burning points, especially in cold weather. That's why beginning in '65 all single point igntion Corvettes got a 1.8 ohm ballast and ...202 coil, and his setup will look OE to the casual observer. The other choice is a current generic ballast and replacement coil that are readily available and inexpensive, but they will not look original.

But first find out what you really have - not just visually - but functionally, and also check that the wiring is IAW the shop manual wiring diagram. Post the values you measure and part numbers of the coil and ballast that you bought.

If you can change a light bulb and have the shop manual it is better for you to do these diagnostics yourself as you are unlikely to find a "mechanic" that has a clue how these old systems work unless he has experience working on vintage cars.

One of the beauties of vintage cars is that they have very simple electrical systems. If you have a basic understanding of DC circuits, a multimeter, and the appropriate shop manual for your car, you can troubleshoot any electrical problem.

Duke

[Joseph U.]

Re: C1 Coil "blown" twice

Thanks Duke,
I know the wiring is correct according to the AIM as I did it myself (with much encouragement from others on Forum). I will do the checks when I get home in a couple of weeks. So if needed can or or should I use a "202 coil" and a ballast resistor for a '65?
Much appreciated help, as you are right that most mechanics don't even know what a carburetor is (except of course via Wikipedia).
Joe

[Duke W.]

Re: C1 Coil "blown" twice

It all depends on what you are looking for as a final solution. Do you have the car judged or are you looking for functional replacements with no regard for original visual appearance or parts?

I referred to the 1.8 ohm ballast and ...202 coil as an example of what will work both functionally and have original appearance to the casual observer. That was the last ballast/coil combination used prior to replacing the ballast with the resistor wire, and it appears to be a durable combination. The 202 coil became the service replacement part for nearly all previous coils for many years, and the 1.8 ohm ballast was the most commonly used ballast across the Chevrolet model line for a couple of decades, but there are some subtle physical details that changed over the years.

BTW 0.3 and 1.8 ohm ballasts of the same era appear identical. The only difference is the wire. Service parts were distinguished by a "black dot" or "blue stripe" and most believe that ID scheme was also used for production, but I've never been convinced.

The least expensive new coil/ballast are the service replacement parts you can buy at any FLAPS... functionally okay, but clearly distiguishable from the OE and GM service replacement parts, while they were available.

I don't know what you could buy from a GM dealer today, but if these parts are available, they might be the same as what you can buy cheaper at your local FLAPS.

Duke

[Joseph U.]

Re: C1 Coil "blown" twice

Thanks Duke,
When I first got the car I was all Gung-Ho to have it as a top-flight car - but to be honest I just like driving the car - it is a beautiful car with a terrific paint job (in Laquer no less). But it is a car I like to drive to local cruise in etc. Really not worth a frame-off restoration to me since then I would be afraid to drive it. So I would like it to look period correct but it does not have to be CORRECT. If you know what I mean. The coil is under the shielding anyway - so all you see is the ballast resistor - and most casual observers would not even know what it was. So sounds like a 1.8 ohm ballast and 202 coil might due the trick and be better than what I have now - whatever that is I guess.
Joe

[Richard M.]

Re: C1 Coil "blown" twice

A running engine voltage test at the coil+ would clarify this, but one other possibility......

Ensure that the Green wire from the Starter Solenoid "R" terminal is properly connected to the "R" terminal and not connected to a direct battery source. This would continually source full battery voltage to the coil, which would be a potential reason the coils are burning up. I don't know if possible, but if the solenoid internal contacts are shorted, it could keep full voltage at the "R" terminal at all times. IMO highly unlikely but worth a check to verify.

As a recap, the additional Green wire from the "R" terminal at the solenoid provides higher voltage to the coil only when Cranking the engine at key START position. Once the engine starts and key is released to RUN, the Green solenoid "R" terminal wire is de-energized and the coil will only see the reduced potential from the Ballast Resistor.

Rich

[Steve G.]

Re: C1 Coil "blown" twice

Periodic maintenance of the primary side of the ignition circuit is always a good idea, however it is extremely unlikely any of it lead to your coil failure.

On the downstream (- or points side)side of the coil,two types of failures can occur, or variations of them. An open circuit (or high resistance) or a shorted circuit (low resistance).

With an open circuit or high resistance little or no current flows through the coil. The coil won't be damaged because for the most part it's like the key is shut off. It doesn't matter that there can be full batt voltage at the + side of the coil, with an incomplete circuit no current flows.

With a dead short, which is what occurs when the points are closed, you have maximum current flow. Obviously that's not harmful to the coil because that's what happens at any time the points are closed. Where you could overheat and damage the coil is if you have a continual dead short, unlike the one created by the points which is constantly being broken by the opening of the points. But if you have a continued dead short the engine quits immediately. So for damage to occur to the coil you would have to walk away from the stalled car leaving the key on. This heating that can occur doesn't happen in a couple of minutes even. It takes a while for a coil to get so hot it will damage itself. More likely the battery will go dead before that happens.

On the upstream (+) side of the coil a short won't damage the coil, the current doesn't make it to the coil, it takes the short circuit to ground. The damage occurs in the system upstream. In an open or high resistance situation, current is reduced to the coil. Not enough current/voltage won't harm the coil.

The primary purpose of the ballast resistor is to extend the life of the points. They are the weak link in the system. Too much resistance in the ballast resistor, reduced flow, no damage to the parts in the system. Could have driveability problems.

Too low resistance in the ballast resistor, high flow, potential for damage to the parts. But the weak link is the points. I've seen lots of point ign systems hobbled together with no ballast resistor at all and the way it comes to light is with the complaint of not being able to keep points in the machine. While I can't say with absolute certainty that you couldn't damage the coil running without a resistor, I've never seen it happen in almost 40 years as a journeyman. And I would say that if you didn't have a waste basket full of burnt points before your coil failed, it's pretty safe to say the ballast resistor didn't ruin your coil.
Steve

[Joseph U.]

Re: C1 Coil "blown" twice

Thanks Rich,
Looks like I need to get out there with my meter and just check all and recheck the wiring.
Appreciate the help and of course the knowledge. Always helps to know a little more.
Joe

[Joseph U.]

Re: C1 Coil "blown" twice

Thanks Steve,
Great information.
Much appreciated.
Joe

[Steve G.]

Re: C1 Coil "blown" twice

Should add, are you certain the crack in the newest coil is actually a crack and not a carbon track?

If you have high resistance on the secondary side, in a plug wire or coil ht wire, the high voltage will seek out the shortest route to ground. If it's high resistance in the coil wire the engine will quit with the short. But if it's a plug wire it can cause a short at the coil only when that plug is set to fire. If it travels this same short circuit enough times it leaves a carbon trail. This carbon track looks remarkably like a crack and is often mistaken as such.

This failure will have other symptoms of course, because each time the current flows down the track that cyl misfires.

Steve