What would kill a new coil?

C

Commander Toasty

Member
Situation is... Roughly 500 miles ago I installed the Perko electronic sensor in place of points using the FS Ignitions kit. They sent me two bad coils (leaking) and I used a brand new 6VDC no external resistor coil from Napa Auto Parts. Ran fine - no issues.

Driving the other day in no special circumstances, about fifteen minutes into it and the ignition simply died. It was the coil. replaced it and things are going fine.

My question is - what killed the coil? I make it a very diligent practice to never leave on the key without the engine running other than the fews seconds of starting. I can't think of anything else.

I run an alternator (again 6VDC) but always have and no issues.

Thoughts?
 
Most modern coils are oil filled and that oil will often leak out if it is mounted the
way the A coil is. I had the same experience till someone told me to mount it with
the hi-volt wire from the top. It may require a longer wire to the dist. but it
cured my problem.
 
The coil definitely did not leak. The first two from the vendor did leak, but the one from Napa did not. Hey - I run a clean engine! :)

But you know it may be possible that a coil designed to run normally upright might not have enough internal oil covering windings when inverted, and so the darn thing may have simply cooked due to no coolant. Sounds like a bit of a reach though...
 
In this day and age, the customer is all too aften the fina quality control station for the manufacturer. "This coil tested by Toasty"! So now it's time to test NAPA's warranty.
 
If there are 100 or more running Model A's here on the forum I would think they would let you know whos coils work and the ones that don't. Once I find out I'll buy one.
 
If there are 100 or more running Model A's here on the forum I would think they would let you know whos coils work and the ones that don't. Once I find out I'll buy one.
Click to expand...

I just got one from the model A vendors. Don't know the brand but no leaks or failures in years.
 
Roadster62 said:
If there are 100 or more running Model A's here on the forum I would think they would let you know whos coils work and the ones that don't. Once I find out I'll buy one.
Click to expand...

I'm still running the orignal points and 83 year old slant pole coil that came with the car. I'll let you know the test results and how it checks out when it fails.:D
 
Ah but there is a difference. The stock 6 volt coil doesn't make very many jolts, just what the points and condenser can handle. The coil used when you put in the Pertronix can handle more jolts = different coil.
 
I purchased two high performance coils a couple years ago and put them on my two cars. I convinced myself the cars ran better. Both of them failed. The first one began failing intermittently at high temperatures out in the desert. Gave me fits trying to figure out what was wrong with the car. Then it failed completely. The second one started doing the same thing, this time I knew what it was. I sent them both back to the manufacturer. They said they both tested ok. When I asked if they tested them at high temperature they said they didn't.

I have since picked up several Model A coils at swap meets for about a dollar. I bead blasted and painted them and put them on the car and they worked.

I don't think a Model A needs a high performance coil.

Tom Endy
 
Commander Toasty said:
Ah but there is a difference. The stock 6 volt coil doesn't make very many jolts, just what the points and condenser can handle. The coil used when you put in the Pertronix can handle more jolts = different coil.
Click to expand...

My stock points and coil makes a spark at least 1/2" long and blue in color. That's always been plenty for any Model A I've run.:)
 
I also get a 1/2"+ fat blue spark from my stock points system, it has been very reliable, always gets me home.

Perhaps your alternator is having trouble with making proper voltage, or is making dirty electric ---adding some AC to the DC due to weak diode--some 1 wire systems have a much higher spike of voltage on startup.

Perhaps you could find someone to look at your system on a scope, that would show dirty electric, and you could see if the electronic unit has altered it's dwell and has the power to the coil on too long
---it could even be the battery ---even though it starts the car--- the battery has another job ---it absorbs the voltage spikes ---with a stock system it is not as sensitive, but you have electronics ---I have seen modern cars with electronics glitches that show AC in the system, and have had several alternators cured with new batterys, the battery acts as a filter, when it is old it may still start the car but it is tired and it's capacitance changes ---some of the new battery testers use this to check batterys by sending in ac signals and and measuring the batterys reaction.
 
Electronic ignitions require a coil with very little resistance. Mallory suggest a 0.6ohm coil for flatheads with a mallory setup.

Something I saved when going through a shelf of coils and testing them to see if they were good or junk. Can't remember who originally posted the information below.

1 test: is primary resistance, checked with a ohmmeter from positive to negative. This resistance is always less than 5 ohms and may be divided into three areara or ranges:
1=low ohms ( less than 1 ohm) electronic ignition only !!!
2=mid ohms ( 1 ohm to 2 ohms) stock units , contact controlled with ballast
3=high ohm ( 2ohms to 4 ohms) stock contact comtrolled no ballast needed.

2 test: Is secondary resistance , checked from secondary out put terminal to either of the small terminal ( pos or neg). This reading is always in thousand ohm settings and usually is 4000 to 7000 ohms.
 
Last edited:
Commander Toasty said:
Ah but there is a difference. The stock 6 volt coil doesn't make very many jolts, just what the points and condenser can handle. The coil used when you put in the Pertronix can handle more jolts = different coil.
Click to expand...

With 4.5 compression you do not need many volts. All you need to do is fire the plug, anything more than that is wasted.
I still run original coils and points.
 
Q

Commander Toasty said:
Situation is... Roughly 500 miles ago I installed the Perko electronic sensor in place of points using the FS Ignitions kit. They sent me two bad coils (leaking) and I used a brand new 6VDC no external resistor coil from Napa Auto Parts. Ran fine - no issues.

Driving the other day in no special circumstances, about fifteen minutes into it and the ignition simply died. It was the coil. replaced it and things are going fine.

My question is - what killed the coil? I make it a very diligent practice to never leave on the key without the engine running other than the fews seconds of starting. I can't think of anything else.

I run an alternator (again 6VDC) but always have and no issues.

Thoughts?
Click to expand...
electronic ignition useage catches my eye here. ive run 12v alternator and electronic ign for five years with great satisfaction. i remember when putting it together, that written instructions strongly stated the proper coil be used, that is to say, what ohms resistance must be....and nothing else...for proper operation! i checked the coil resistance with an 'ohmmeter' to ensure using proper coil. i settled on a coil with an 'internal' resistor with proper ohm rating, as i did not want the 'ugly' appearing old external resistor mounted on my firewall. mounted the coil upright, as i could not think of a reason why a coil should/would be mounted upside down? auto elect is baffleing to me, but mabe coil would fail if directions not followed:confused:.
 
To answer the orginal post.

What killed the coils? The answer is always the same ( assuming its a quality coil to start with) , the coil died because of excessive heat and the heat came from too much current !!!
Too much current was caused by low resistance and low resistance came from incorrect balance of parts!
Simple answer right ???

A . 5 ohm coil would use on a 12 volt car , 24 amps . Way high for most systems. Todays cars with .5 ohm coils use some very complex electronic controls for current limiting etc.
The same car with 4 ohms would use 3 amps , which would run the car almost forever and not overheat the ignition..........:eek:
 
Since it is a Pertronix ignition I asked them what coil to use and got a surprising answer: Their part number 40111. This is an epoxy coil that doesn't use oil, which makes sense. And it is a 1.5 ohm coil. They also make a 3 ohm and a .6 ohm coil, different part numbers. But the surprising part is that their application guide shows this coil for 8 cylinder 12 volt cars, and shows a different coil for four cylinder 6 volt cars (.6 ohms). I double checked with them pointing out I have a 6vdc car and they confirmed the 12 volt coil will work and is appropriate.
 
Tinker said:
Electronic ignitions require a coil with very little resistance. Mallory suggest a 0.6ohm coil for flatheads with a mallory setup.

Something I saved when going through a shelf of coils and testing them to see if they were good or junk. Can't remember who originally posted the information below.

1 test: is primary resistance, checked with a ohmmeter from positive to negative. This resistance is always less than 5 ohms and may be divided into three areara or ranges:
1=low ohms ( less than 1 ohm) electronic ignition only !!!
2=mid ohms ( 1 ohm to 2 ohms) stock units , contact controlled with ballast
3=high ohm ( 2ohms to 4 ohms) stock contact comtrolled no ballast needed.

2 test: Is secondary resistance , checked from secondary out put terminal to either of the small terminal ( pos or neg). This reading is always in thousand ohm settings and usually is 4000 to 7000 ohms.
Click to expand...


The coil that failed is a Napa IC7. And it measures good at 1.5 ohms primary and 9000 ohms roughly secondary to both posts.
 
You must log in or register to reply here.
Back
Top