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32 Cadillac V-12 Ignition System Questions


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I will be starting my tuneup / checkup on this car with the ignition system and have some questions for the experts:

1. Is it possible to use a dwell meter / tachometer with this 6V dual coil system and if so how do you hook it up? If it is possible, what should the dwell reading be?

2. What type of currently available spark plug will work for replacement?

3. I will do a compression test while the plugs are out, what should the normal reading range be?

4. The spark plug cables are old and may even be original with metal number rings on each, the rubber distributor boots are in bad shape and there are no boots at the plug ends. Can anyone recommend a supplier for a correct reproduction set of cables?

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Guest stude8

I have a Sun Distributor #504 test machine and have accumulated data books for it as early as I could come across them. The 1944 book only lists Cadillac back to 1940 8 cyl models.

It does describe how to adjust Lincoln V12 distributors that have 6 lobe cams,they adjust the movable set to 22 1-2 degrees apart from the fixed set. Then each set of points is set for 36 degrees dwell.

The theory of dwell angle for an engine is related to how many cylinders are fired in 360 degrees of engine rotation, thus 360 divided by 12 = 30 degrees. <span style="font-weight: bold">BUT</span> another factor is how many cam lobes on the distributor shaft? I think your dual coil system will have 6 lobes so that one set of points fires 6 cylinders and the other set the remaining 6 cylinders.

I owned a 1930 Studebaker President 8 for a long time that had a dual coil dual point Delco distributor that operated similar to the way I think yours works but it is only a guess since I have only seen one 12 cyl Cadillac once (a 1931 sedan).

The Stude distributor had one point set mounted on the fixed breaker plate and the second set was on a movable plate so it was possible the adjust the two sets exactly 45 degrees apart. Then you adjusted dwell one set at a time by insulating the opposite set with fiber paper between its points to remove them from the circuit.

I don't believe the modern "Dwell" method was used in the 1930's so written data is not seen in service literature of that age.

You would be wise to locate someone in your area with a Sun or other stroboscopic distributor test machine to run your distributor on. That way it can be setup to exact accuracy and replaced in the engine without any guess work.

If you lived near Harrisburg, IL I'd say come over some day and I'll run it for you. Stude8


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Thanks Keiser, I'll check with Egge.

Stude8, thanks. I was afraid that the dwell was a later method, its not mentioned in the shop manual. I have been told that the Cad V-12 is set up as like two inline 6 engines running off the same crank. Each bank has the firing order of a straight six with a separate ignition system and you can actually disconnect the coil to one side and the engine will continue to run smoothly. (I have not tried that yet) The shop manual gives a very complicated method of setting the points tied in to overall engine timing which I have read a few times but still do not fully understand. What I really need is someone who has done this chore successfully to translate the process into simple terms, any takers? Since the car currently runs well I do not want to screw anything up until I have a better understanding of the system.

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Guest stude8


I see in your profile you have a 1928 Pierce, does it have the Delco 668A or C distributor? That is the same distributor used by the Studebaker President 8's from 1928 thru 1931. In fact in my photo in the previous response the distributor on the Sun 504 is a Delco 668C dual ignition 8. If you observe close, there is a coil primary lead at 8 o'clock with the red clip lead on it, there other is at 2 o'clock unconnected. The photo was made while actual "Dwell" was being read for the 8 o'clock point set on the lower left meter. So you should be able to read your dwell one set at a time on the 12 engine while it runs with the appropriate connection on your distributor.

From the Sun manual for Lincoln 12:

"It does describe how to adjust Lincoln V12 distributors that have 6 lobe cams,they adjust the movable set to 22 1-2 degrees apart from the fixed set. <span style="color: #000099"><span style="font-weight: bold">Then each set of points is set for 36 degrees dwell."</span></span>

You can read them just for reference without changing anything and observe if they are equal and what they read.


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