1924 sedan coil issue

[Todd Puzey]

I’ve been taking my 1924 sedan out for short trips for fun I. The summer sun, and I have been having a coil issue.

My coil is the square type mounted towards the top of the firewall on the passenger side.

What happens is that the car starts easily as it usually does, and then I take it for a drive. Once the engine is hot and if I shut the car off, the car will not start again and if I take the coil wire off the distributor cap and ground it while turning the car over there is no spark.

if I then pull the car into the shade, or my shop and let it cool down for a 1/2 hour or so it fires right up again easily.

Has anyone else had a similar issue with your coil? I know there are threads about issues with replacement coils, so what would you gents suggest I do for a replacement?

[Mattml430]

Sounds more like a fuel vaporising issue. 
Not ruling out the coil could be breaking down under hot conditions though also. 

[Todd Puzey]

Checked the fuel supply each time and the float bowl was full of fuel, and again each time I checked for spark from the coil when it did it and spark was absent directly from the coil until it cooled down.

[edinmass]

Likely a coil. Easy enough to swap one out and test it with the new one. I have a coil tester that heats and conditions the coil. They are not common and almost no one uses them anymore. See my video below. Be sure to get a correct coil……….Dodge may be 12 volts if I remember correctly. Even modern coils today have a high failure rate…….too much Chinesium in production parts today. 
 

 

[Todd Puzey]

9 minutes ago, edinmass said:

Likely a coil. Easy enough to swap one out and test it with the new one. I have a coil tester that heats and conditions the coil. They are not common and almost no one uses them anymore. See my video below. Be sure to get a correct coil……….Dodge may be 12 volts if I remember correctly. Even modern coils today have a high failure rate…….too much Chinesium in production parts today. 
 

 

good tips and yes my car is 12volts

[Mark Gregush]

Make sure when you get the replacement coil it has either a built-in resistor or you need to add one. Not all aftermarket ignition parts are made in China, they are made in Mexico too. 

Edited July 24, 2023 by Mark Gregush (see edit history)

[nat]

6 hours ago, Mark Gregush said:

Make sure when you get the replacement coil it has either a built-in condenser or you need to add one.

     I think Mark meant to say "built in resistor".  Without that the points will fry.  

     Try a new 12V coil, (with a resistor if the coil doesn't have one built in), and see if that brings you any closer to motoring bliss.

[Mark Gregush]

4 hours ago, nat said:

     I think Mark meant to say "built in resistor".  Without that the points will fry.  

     Try a new 12V coil, (with a resistor if the coil doesn't have one built in), and see if that brings you any closer to motoring bliss.

Fixed my post. Yes resistor.

[Todd Puzey]

Thanks for the advice gents.

when you guys suggest a new 12v coil, are you meaning a modern canister coil, or a new restoration style original coil.

[Mark Gregush]

29 minutes ago, Todd Puzey said:

Thanks for the advice gents.

when you guys suggest a new 12v coil, are you meaning a modern canister coil, or a new restoration style original coil.

For me, with unrestored 1920, modern. Mine sits in the housing that the old coil was fitted into. Guess that depends on which way you want to go.

[keithb7]

Are you guys referring to some type of built-in ballast resistor? Is this only needed for the 12V cars? Which this 1924 Dodge is. My 1938 6V Mopars do not have this coil resistor that you speak of. 
 

What is the purpose of the ballast resistor, if needed? To lower the voltage going to the coil? Thx.  (Learning every day here)

 

Keith

[nat]

13 hours ago, keithb7 said:

Are you guys referring to some type of built-in ballast resistor? Is this only needed for the 12V cars?

     Yes, Ballast resistor and no, I've never seen one on a 6V system.  It drops the voltage to about 8V.  An external resistor can be bypassed while the starter is engaged to compensate for voltage drop while cranking.  That's not necessary on a 12V DB.

     Like Mark's, mine sits where the original coil was.  I put a piece of 1/8" cork gasket under and around it as a bushing and cushion.

     I once rewired an early 60s F100 truck.  It ran terrible if at all.  The original positive wire to the coil was carbon resistor wire. 

[22touring]

"What is the purpose of the ballast resistor, if needed?"

 

In order to step up the battery voltage sufficiently to fire the plugs, the coil needs to have a very high primary-to-secondary turns ratio. There are two ways to increase the ratio: by adding turns to the secondary or by reducing the number of turns on the primary. Reducing the number of turns on the primary is much cheaper, but then the primary draws too much current and fries itself.  The ballast resistor is to prevent the primary, having just a few turns, from drawing too much current after the car starts. When cranking, the ballast is bypassed momentarily so you get the maximum spark voltage.

[Mark Gregush]

3 hours ago, nat said:

I put a piece of 1/8" cork gasket under and around it as a bushing and cushion

Great idea! Mine is just sitting there bouncing around...oh wait, our roads are really smooooth! LOL

[JACK M]

3 hours ago, Mark Gregush said:

..oh wait, our roads are really smooooth! LOL

You must be using different roads than I use.   🤣

[Bloo]

If car is 6V, and you are using a normal looking canister type 6V coil as a replacement, the type used on later 6V cars up through 1955 or so, do not use a resistor. If a resistor remains in place, bypass it.

 

6V coils that use ballast resistors exist, but to the best of my knowledge are all strange form factors, like coils for Ford products with "crab" distributors, Buick "mailbox" coils, the coils with the output post on the side used on some Dodge Brothers cars, etc. I hope to be proven wrong on this point but have not been for several decades now. For any normal cylindrical 6V coil you can buy in a parts store, do not use a resistor.

 

On a 6V car you could probably use a 12V coil intended for use with a resistor, and just not use the resistor. These coils ran on about 7 or 8 volts, not far off from what a 6 volt coil runs at when the battery is full and the generator is charging. There is no good reason to do this as long as 6V coils remain readily available, but it would probably work.

 

On a 12V car, you have 2 choices. You can run a 12V coil intended for use with a resistor (but then you must use a resistor), or you can run a 12V coil meant for use without a resistor.

 

For a 12V coil that uses a resistor, almost any coil from a 12V American "big three" car from the mid 50s forward should work. Chrysler's coil is a good choice because Chrysler used ballast resistors long after most other 12V American cars had switched to resistor wires, and the matching Chrysler 1 Ohm (approximately) resistor is available through almost any parts store. If you are using some resistor for another coil, like maybe one that came with the car, make sure you have about 7 or 8 Volts measured between the coil supply post and ground with a full battery, the engine running, and the generator charging.

 

For a 12V coil that does not use a resistor, a Bosch aftermarket "Blue Coil" may be a good choice. You'll probably want to paint it.

 

Edited July 25, 2023 by Bloo (see edit history)

[nearchoclatetown]

The blue Bosch coil is a high output VW coil and has an internal resistor. They should be easy to find, fits most VWs from '67 up into the '70's.

[Mark Gregush]

On 7/25/2023 at 11:01 AM, JACK M said:

You must be using different roads than I use.   🤣

LOL Ya more then likely not, no matter which part of this great state we live in!