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cadmanof50s

Spark Plug Question

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Just rebuilt the engine for my 1948 Cadillac (346 ci L-head). The shop manual calls for an AC Delco Plug #104.

I have been seearching the WEB going in circles to find a modern suitable replacement. I can probably get a set from eBay, but I am reluctant to use plus that are potentially 60+ years old.

I would much rather (if possible) use a newer replacement.

Could someone suggest a substitute plug.

Thanks in advance,

Vic Brincat

a.k.a. cadmanof50s

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Benefits of AACA Membership.

I would check with a Champion cross chart. As for using a 60 year old sparkplug, as long as it is not damaged, rusty, etc... I would not see a problem. AC used basically the same process in manufacturing spark plugs for most of the time they made them.

Edited by Larry Schramm (see edit history)

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There is nothing in a spark plug to deteriorate with age. NOS plugs that are not rusty will be as good as new. Possibly better. Your engine and ignition system was made to use a certain plug. A modern substitute may not be identical and may not work as well.

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The Autolite website has a reference for most makes back to the 1920s that gives current Autolite plug numbers.

.

PS - just checked Autolite.com and saved you the trouble, #3136 is the currently recommended non-resistor plug for your engine

Edited by Owen_Dyneto (see edit history)

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I was thinking about the non resistor part when I wrote my answer. Good to know they are still available.

Incidentally when the Caddy was new, they did not replace spark plugs all the time. If you took the car to the dealer for a tuneup they would have sandblasted the plugs, and regapped as part of a tuneup. They did not replace them until they were worn out which might have taken 50,000 miles.

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Thanks everyone for the quick response. I am going to try the Champion cross reference, first. But I will certainly keep the other suggestions in mind.

Many thanks!

Vic Brincat

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Though it may not matter to you, there may be an authenticity issue with Champion plugs, they have bright cadmium plated shells which are really only appropriate for later cars. The Auto-Lites have black-oxide shells appropriate to the era.

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The new AC number for the Caddy is a AC M-8. Those you can still get at most any auto parts store like a NAPA or Carquest.

Should you ever have to use a new spark plug that is cad plated for a older car, I'll pass on a little trick. Use a broad tip black magic marker and 'paint' over the cad plating with it. Once the plugs get hot from running, it will bake itself and the finish will look just like it should. It will last for years. BTW ~ The AC M-8's are already black.

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When did they start cad plating the plugs? I only started working on cars in the early 60s but don't remember a time they weren't available.

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Different manufacturers plated their spark plug shells differently. AC Sparkplug always had as long as I can remember black oxide metal shells plated in a process called udylite plating(I think spelling?) Champion had a silver color plating on their shells.

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Green Spark Plug Company Ltd has AC 104 plugs. Their website is:

Green Spark Plug Co Ltd - Search

Green is in the UK and I have purchased Lodge CNY plugs for my Triumph from them. The AC 104 plugs are 2.75 pounds each and at the current exchange rate of around $1.50 to the pound that comes out to around $4.10 each. As I recall the shipping was around $15.

They currently have 11 in stock.

Bob Beers

Check out my website at: Bob's Vintage Cars

AACA, VCCA, VTR, TRA

1933 Chevrolet

1962 Triumph TR4

1984 BMW 633 CSi

Edited by Vila
Addition on quantity (see edit history)

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