Early spark plug question

[Terry_007]

Let me begin by saying I'm well versed in the chronology of Ford T spark plugs. As a 50 year collector of plugs, I have examples of plenty, plus lots of info and advertising, so this isn't a question about anything other than just this one plug.

It is a 3/8 inch tapered thread plug bearing Ford script on the porcelain. Plug construction resembles those made by Bethleham (The Silvex Company, Bethleham, PA), although this looks more like those produced by them in the 20s. I have been told it was a plug Ford intended to use in the earliest Ts (perhaps a few of those built late in 1908). I can't find any reference confirming that though. Based on my experience the plug itself also seems much later than the 1908 era. The one-piece construction is not often seen until much later into the 20s. The Silvex Company was not even founded until 1912.

Does anyone have information about this plug and what it might have been used for? I'm hopeful there is some documentation available for it. So far, all I've got is speculation ranging from "salesman's sample" to the early T story. There were hundreds of aftermarket plugs made for use in Model Ts (and any other of the many cars using 1/2" pipe thread plugs). Could this just be another example of one? The smaller thread is something nobody seems familiar with.

Thanks in advance -

[Steve Jelf]

I believe the ⅜" NPT thread rules it out as a Model T plug. If Model T plugs were ever a size other than ½" NPT I expect the encyclopedia would say so, and it doesn't. But how about Models A through S? Do any of them take a plug that size? That wouldn't surprise me.

[Wayne Sheldon]

Terry B, If you don't know???? Yours is the first name I would think of if I had a serious question about any early spark plug!
Like you, I agree it is post 1920. The way the porcelain is crimped into the base pretty much clinches that.
I do know, that there was an obscure early model T plug size used on export model Ts around 1909. However, I cannot believe this would be one of those (due to the base design). Whether it is in the encyclopedia or not? Better researchers than I have shared build sheets from the earliest model Ts that list the car being manufactured as an export and using the undersize plug. I do wish I had a link to one of those threads.

How about some more pure speculation? I also know that a few European built model Ts used a smaller engine than the standard model T engine. They had a smaller bore to reduce European horsepower taxation. Is it possible that they used an undersize plug? This was done during the 1920s, and I don't think very many such cars were actually built. Only a few times on this and other forums have those cars been discussed at all. Several overseas forum members mentioned them in relation to other discussions. I don't know if any of those cars or engines still survive?
There were also the European Fords built in the early 1930s that resemble undersize American Ford V8s? The Ford plant in Germany built a lot of those cars in the mid 1930s.

Interesting plug to be sure! I hope someone that recognizes it can stumble onto this thread and provide a real answer.

[ABoer]

We have an engine # 70784 with Metric M 18 plugs .

Toon

[ABoer]

We also have a model t with Firestone Polonium Plugs .
How long are they active ???

Toon

[Wayne Sheldon]

Anthonie, Radioactive polonium has a very short half life. As such, the radioactive decay should have rendered them relatively safe after only about ten years.
Radioactivity was not well understood back then. Some engineers believed it would in effect amplify the spark for better ignition! Probably little to no real advantage from it however.
I would recommend handling with care. The remaining minute amount of residual polonium could still be toxic.
Those are a wonderful curiosity, and a great collectors item. I have a few of them myself, a couple NOS with original boxes.

[TXGOAT2]

Could the plug be for a Lincoln?

[Jerry VanOoteghem]

My guess would be, that it was made by an aftermarket plug manufacturer trying to cash in on the Ford name. If true, they were also trying to be sued. As to the theory of it being a plug for a very early, or even pre-T, car, I don't think so. Aside from its construction, I doubt Ford would have wasted his time thinking about a Ford script sparkplug when he had much more to consider in the design & build of the "new model".

As for it being for a Lincoln, post 1922, I would think the plug would then be marked "Lincoln".

All guesses on my part however...

[TXGOAT2]

The script on the plug doesn't look right to me. Maybe it's for an English T or A, or an English V8 60, or some other overseas Ford product.

[Rich Eagle]

The script looks pre-T to me. I've never seen a 3/8 NPT before. Might have been made for one of the experimental engines?
Good puzzle.
Rich