Correct condensers for '40 distributor

Ford and Mallory worked together to get the coil design for the engine front mounted distributor to work as reliably as was possible for the time. Inductor coils for battery ignition systems aren't all the same. Ford used the can type on the model A but the front mounted set ups made it more of a challenge. The first V8 set ups used one that looked like a can type but it must have been problematic for some reason. This seems to be the case because the later ones were much shorter which would have made a difference in the magnetic resonance and the inductive reactance of the coil. The ballast resistor was added to control the current input and likely to lessen the amount of back flow voltage that happened when the points opened up. It was still high enough that they needed a capacitor with a high enough capacity and voltage tolerance to keep the points in good condition longer.

The engines were low enough rpm in that time frame that everything worked fine to get 8 strong sparks for every 2 revolutions of the engine. At higher RPM an even higher cap rating is better for the overall average but the flathead is not a real high rpm engine like the OHV types. When Ford went back to the can type coils in the 8BA era then the change went back to lower capacity condensers and no more need for a ballast resistor.

The condenser has to be matched by capacitive reactance with the inductive reactance of the coil under the average conditions of the engine's operation. There are formulas a person can use to tell what best capacity range of the condenser to the coil that is going to be utilized in a design. All this stuff is transistorized in the modern era plus dwell time can be manipulated however they want it to be now.
 
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rotorwrench,
I recently had an issue with one of the replacement type V8 condensers mentioned above that mount to the coil mounting screw and were NORS. When I first installed it the car started right up and performed fine. After I put about 200 miles on it, the car was hard to start and then when it did start it idled OK, but would not take throttle - bad miss, backfiring, rough running, etc. I happened to have some brand new old stock Autolite condensers still in the original boxes with the pigtail wire (which weren't correct), but I installed one and the car has run perfectly since then. I'm not so much concerned with "correct" as I stated in my original post, but more interested in strong, durable condensers that can handle the task and not break down after a few miles of use. I'm also using a new Dennis Carpenter coil, so it didn't appear that the coil was the culprit...the car's running fine now with the condenser change. Those pesky condensers are the cause of a lot of our ignition problems.
 
I used new condensers supplied by Third Gen Auto on the last two distributors I rebuilt with good results. I typically use the 1937 style and cut the bottom of the hoop out so I can pull the coil by loosening the distributor mounting bolt instead of removing it entirely.
 
38 coupe,
Yes, I've done that too with the original type condensers in my parts stash, but I've run out of good ones. Trouble is, I don't know who has good quality condensers I can rely on any more. I refuse to knowingly buy any foreign made junk. Thanks for the recommendation on Third Gen.
 
Some of the old condensers were made with mica instead of wax paper for the insulator. The mica based ones will have much more longevity that the wax paper types. It just depend on the materials in this case. I can't tell you which are which with out doing a post mortem on the old parts. Only the original installer may remember where the part came from and what brand it might be.

Keep in mind that the condition of the other components also have an effect such as an old tired ballast resistor or an already worn set of breaker points. One set of points breaks the circuit and the other closes the circuit to improve dwell time. Dwell time was important for the old Mallory design coils. If any of this stuff is suffering wear or maladjustment due to wear the other components will start to suffer as well.
 
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rotorwrench,
I never thought about the ballast resistor giving problems. Is there a way to tell if your ballast resistor is tired or should I just replace it? Mine may be the original.
 
Checking the Ohms value will tell if it's within specs but it doesn't account for how heat affects it after it gets hot. Checking the current flow to the coil is about the only way to tell how it's doing.

Originals were good resistors. Replacements not so much. If it's still functional then keep what you have until it flakes out. NOS ones are likely harder to find as well as good used ones.
 
mcgarrett said:
rotorwrench,
I never thought about the ballast resistor giving problems. Is there a way to tell if your ballast resistor is tired or should I just replace it? Mine may be the original.
Click to expand...
When I first got my '40 and was chasing a weak spark condition, I thought I had a bad ballast resistor. Tried a new repro resistor, and four different used original resistors supplied by VanPelt. All tested very close to the original on the car. Problem was elsewhere. My conclusion from that experience is:
the ballast resistors are quite robust, most old original resistors still perform as designed.
 
rotorwrench said:
Some of the old condensers were made with mica instead of wax paper for the insulator. The mica based ones will have much more longevity that the wax paper types.
Click to expand...
I have read that a NOS condenser can be assumed to be bad. Humidity in the air will cause the internal insulation to break-down over time, even just sitting on a shelf. Do you agree with that?
 
JayChicago,
Yes, I completely agree with that. I've heard that from some of the old timers in our hobby, and I'm not about to argue with them! :). I also think that a lot of aftermarket condensers were not manufactured to the same standards as those made by the OEM's. I've had problems and downright failures with aftermarket NORS condensers from the flathead era, even still in the factory boxes working poorly, or not working at all. I stay away from them. I'm thinking about adapting one of the newly-made condensers sold by the Model A suppliers they call a "no burn-out" condenser. Others here have given me some other great options that I want to look into as well.
 
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