coil

daveymc29

daveymc29

Well-known member
So here's the story, got a friends car together with a rebuilt B engine, 30 coupe. For some reason he has 12 Volt system. Coil burned out after car had set for several months, I went over to teach his wife to drive it and we ere venturing out I noticed it didn't have much power, drove it home and barely got it to pull up his short driveway to get off the street. I went to get a friend to come assist me in evaluating what had gone wrong, as we had loads of power when we had installed the engine several month prior. He and I did a short drive and put it back in the driveway. Consensus was the coil so I put my hand on it and found it quite hot after perhaps 10 minutes of driving. We took a look with a flashlight and the coil was leaking clear oil, profusely. Shut car off and went for a coil to remedy this problem. Coil says to install with external resistor no other specs. We had to get car out of the sidewalk so we fired it up with just the coil and no resistor and moved it 10 feet and shut off the power. Saturday we intend to go back and get a resistor and be done with it. The question is what specs to ask for, the coil box has no clues. Also these new coils are oil filled and I have been told they should be mounted with the lead out to the distributor UP, not down as in the Model a era, as the cooling effect of the oil can be lost if installed as we always did in the past. Any feelings for you folks on these issues?

Thanks ever so much, in advance. We'll heed the vote tally.
 
With a 12 volt system I would use a three OHM coil , no resistor needed . I run the Pertronix flame thrower coil . I use the epoxy filled version that can be mounter just like the model A coil with the terminals at the bottom . The model A came with a solid tar filled coil . The epoxy filled coil is also a solid coil . Its best not to use an oil filled coil on the model A . When an oil filled coil is mounted in the model A manner oil can leak out. The upper coils inside the coil won't be completely covered with oil and will overheat and failure will soon follow .

Usually if the coil requires a resistor , it is a six volt coil . The resistor allows a six volt coil to be used on 12 volts by preventing the full 12 volt charge from entering and burning out the 6 volt coil . I prefer to use the three OHM coil and get full advantage of the twelve volt volt system , not just the lights and starter . Just to say , three OHM for 12 volts and no resistor is necessary . A 1.5 OHM coil can be used on 6 volts with no resistor . If a 1.5 coil is used on 12 volts a resistor will be necessary
 
6-volt systems with a can type coil are near 1.5 Ohm on the primary winding and don't need a ballast. On 12-volts, they need a 1.3 to 1.5 Ohm ballast resistor. As was mentioned, the 3.0 Ohm are designed to use 12-volts with no ballast.
 
I haven't had much success with the new off the shelf oil filled coils, 12 volt 3 ohm internal resistance type. They over heat, engine stops and needs to cool off to run again or not at all as Purdy states above. Stay away from Lucas, Std,, etc. all made overseas perhaps poor quality control.The oil filled need to be installed with terminals up and longer lead to distrib. cap. Some of the Bosch blue are made in Brazil and may be better. Some say the Pertronix epoxy doesn't dissipate heat well. The Pertronix latest website states one can use epoxy with inductive (points) systems and would appreciate more input on how successful these coils are.
I haven't found any other paste filled coils on the market.
 
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Coil- 1.4 ohm no ballast resistor = 6 volt system
Coil 1.4 ohm use ballast resistor = 12 volt system

Coil 3.0 ohm no ballast resistor = 12 volt system
 
Be aware that Pertronix makes both an oil filled and an epoxy filled 12v 3 ohms coil. You want the #40611 epoxy coil not the #40511 oil filled. Ensure you connect it correctly also (ground side toward points).

I have had my Pertronix coil on the Town Sedan for ~4½ years with no problems.
 
I have had excellent service from the Pertronix three OHM epoxy filled coils on twelve volts for many years without any problem. I also get performance that can be felt with these coils . I know, I know , that the very mention of improved performance will scare some off , too bad !!! The oil filled coils are usually cheaper but must be installed with the wire connections pointing up or the coil can overheat and cease to function . I would never use an oil filled coil on my model A's unless it was the only coil that I had and it would only be temporary .
 
I use Pertronix Flame Thrower coils on both my "A's".:cool: The '29 is 12 volt negative grnd and the '31 is 6 volt positive grnd. I don't remember the part numbers for them, but they are both epoxy filled.;) Mr. Purdy Swoft knows what he is talking about.:)



Bob-A:D
 
While some cheapy coils may have oil in them, the old originals did not. They all used tar. Now tar will liquify if it gets real hot but that generally only happens when the unit is in constant electromagnet state due to the ignition switch being left on with the breaker points in the closed position. This will burn the pimary winding in most cases and end the poor things misery.

Epoxy won't liquify when it gets hot. It will likely soften but that's about it. The primary winding can still burn out if the switch is left on till the battery is dead. All coils are vulnerable to this.

I always get a kick out of names like "Flame Thrower". It makes it sound like it puts out mega joules of spark when in fact it can put out little more than any other coil with the same ohm resistance. If it works good then that's great but any coil can work well if made with good quality materials. The Bosch blue coils have been mentions as being reliable as well.
 
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So we pulled the burned coil, went to the store and bought a blue coil, 12V that plainly states required a ballast resister. Small argument as my cohort said it was not required, so we put it on. Drove some and I told him to touch coil. This cured the argument and we took coil off, remounted with the leads all up and a resistor in the system. Now car runs great, no overheated coil, he cancelled order for a high compression head and gasket plus new leak less water pump and we went home. Owner is happy and it didn't cost us any extra as we had an old resister that worked fine and the small wire with two eyes on it to extent the leads out of the junction box and now the car has once again full power and I, for one, convinced further coil problems are way down the road. I think my cohort may be home ordering resisters for his cars as he has converted all to 12 Volt and none have resistors. If he brings his car to coffee tomorrow, I will check his coil temperature as he told me he has never had a failure in eight or so cars he has converted and none have leaked though he mounts them all in the normal Model A fashion. oil filled coils and 12 Volt. Maybe he is lucky so far.
 
On 12v with 6V coil and series resistor, power dissipation of the coil is halved. 1/2 dissipated by the coil and 1/2 by the resistor. Advantage of the coil not heating up as much.
 
There is only one resistor inside a coil. It called the primary winding.

When Ford made the new distributors for the V8 engines, they were sensitive to heat since most of the coils had a plastic outer shell and not at all designed like the can type coils. Ford started using a ballast to cut the current draw back a bit. They make a good high tension spark on just 4-amps. They used these ballast resistors till 1948/49 when the coils went back to the can design beginning with the 1948 Ford bonus built trucks.
 
I have used the Pertronix 3 ohm oil filled coil with 12 volts for a number of miles without issue. The Pertronix oil filled coil is designed to operate in any orientation, including the Model A firewall, very good quality.

A's Always Dave
 
I think that was rigged. No telling how much amperage they were hitting that coil with. When running as an electromagnet, they get hot fast. When running as an inductor, where there is pulsating direct current controlled by some sort of breaker with at least one spark plug on the secondary, then they shouldn't get near as hot.
 
Radiator overflow (Valve)

You all seemed to have had fun with the coil question so now let's move on to another question the owner hit me with. He put a roofing nail in the overflow pipe to slow water being forced out the overflow and that seemed to solve his problem. I had mentioned that I use a 2.5 lb. radiator cap mounted on a neck down at the outlet end of the overflow tube. That and a piece of rubber gasket on the radiator turn my system into a pressurized system, though only 2.5 lbs. I further added an overflow tank hanging on the radiator support rods and put a dab of water in that which makes a closed system of sorts and if I get the level up a bit in my overflow on a long hill it soon sucks back down as soon as I reach the crest. I saw a similar thing without the tank, just a 2.5 lbs pop off valve on the end of the overflow tube. Can't find that anymore, but it claimed to hold the overflow in most of the time if it was just from the pump throwing the water out. The owner wants to buy one of those valves and I don't have a source to give him. Anyone follow what I'm recalling here?
 
Skip has been making overflow valves for years. I think they are 3 psi. Sealing up the cap area can be a job unless folks do away with the motormeter type setups and go back tho the stock type cap.
 
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