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03-17-2023, 01:29 PM | #1 |
Junior Member
Join Date: Jan 2023
Posts: 25
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Ignition coil resistor on Mercury or Truck engine?
I purchased a 1940 Tudor sedan a few months ago and in the process of sorting it out, I found that the ignition coil resistor has been eliminated. Both wires are connected together on the same terminal on the resistor under the dash. I also found that the car does not have its original engine in it. The casting number on the heads is 81T and the number stamped on the rear of the head is 81T-0050. I believe this is a Mercury or truck engine? The intake manifold boss in between the heads is raised about 1/16". Does that also mean the engine is newer than 1940? The engine has a Crab style distributor on it with an external coil located on the left cylinder head. I have two questions: Should the crab style distributor still use a resistor and what is the resistance of the resistor under the dash so I can see if it is any good? Thank you, Gil
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03-17-2023, 06:53 PM | #2 |
Senior Member
Join Date: May 2010
Location: Melbourne Australia.
Posts: 2,079
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Re: Ignition coil resistor on Mercury or Truck engine?
I guess you still have a 6 volt system and the ignition coil is the original bakelite FORD type which runs on about 4.5 volts through the ignition resistor. The resistance of the resistor should be about .4 ohms COLD and could be about .6 ohms when HOT. If you have a non genuine round canister coil fitted then you need to measure the primary winding resistance in ohms. The combined resistance of the coil primary winding and the ignition resistor should be approx 1.5 ohms only on an original FORD bakelite type coil. Current draw in the ORIGINAL FORD coil primary circuit with the engine stopped (dist timing points closed) is approx 4 to 5 amps and with engine running is approx 2 amps depending on engine RPM. You can see how important it is to have the correct ignition coil. Too much current flowing in the coil primary circuit will reduce the life of the distributor points. Regards, Kevin.
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03-17-2023, 08:31 PM | #3 |
Senior Member
Join Date: May 2010
Location: Wisconsin, USA
Posts: 9,008
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Re: Ignition coil resistor on Mercury or Truck engine?
You have a '41 or later block. The so called "raised deck" blocks were built beginning August 1940; too late to have been installed in a '40 upon an assembly line. You really can't count on the heads to identify the engine. Lord knows, they could have been changed one or more times.
Pulling a head would go a long way to identify what you really have. With that crab type distributor and NO adapter plate, it's most likely '42 - '48. But still, the cam could have been changed during the past. Are there any casting numbers on the bell housing?
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03-17-2023, 09:58 PM | #4 |
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Join Date: Jan 2019
Location: Chicago
Posts: 732
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Re: Ignition coil resistor on Mercury or Truck engine?
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03-18-2023, 09:06 AM | #5 |
Junior Member
Join Date: Jan 2023
Posts: 25
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Re: Ignition coil resistor on Mercury or Truck engine?
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