I just acquired a full case of 10 NOS Bethlehem spark plugs. They are a unique "fire ring" type of design. The display shows the "5 point" type of plugs in the picture, but the little boxes have "type A" listed on one end and also "5 point" on the other end. ???? At 5.00 each I could not pass it up. . I may carefully try 4 of the plugs to see how they work. Then clean them up and put back into the display.
Interesting find Donnie. But Iím confused. The actual plug looks nothing like the illustration on the display box. What am I missing?
I have a Bethlehem or two, but nothing like that. How is that thing supposed to spark without any electrode?
Steve, instead of no electrode Insuspect those plugs have a HUGE electrode. I wonder if you could set the gap by moving that centre button in and out? I seem to remember seeing some antique airplane spark plugs that worked like that, just with a less exaggerated design.
Donnie, hard to tell from here but, are the threads 1/2" NPT? Also it doesn't look like there are enough threads to hold the plugs very well. Did someone put different plugs in the boxes? Very interesting for sure! Dave
David,those are neither Ĺ"NPT or ⅞-16.
They in a general way resemble the plugs I got out of a WW2 target drone engine.
Yeah, Donnie B, I don't think those are the Bethlehem plugs for the Ford car. However, they are an incredible find and well worth what you paid for them. They do look like they might fit my gasoline carriage motor. If you decide to keep the boxes (THOSE are wonderful!), and maybe try to fill them with some Bethlehem plugs and sell these odd plugs? I may be interested in a couple?
I may even have a Bethlehem plug or two for a Ford myself? I would have to go look. I never really collected spark plugs myself.
Here is a Bethlehem 5 point - a bit worse for wear but you get the idea.
Those are Bethlehem "Lifetime" aviation or motorcycle plugs with an 18mm (Model "A" Ford) thread pitch.
The outer cover helps keep the inner mica or porcelain insulator from being damaged by road dirt on a motorcycle or from debris picked up by the propeller from a dirt air strip in an aeroplane. The holes allow some air circulation for cooling.
Somehow they were put in the wrong boxes, but I'll bet they are harder to find than the "5 point" type.
A GREAT find!
WOW, Ive been away from the computer all day, sure are a lot of responses. . Im also confused about the plugs.
Here is what I found out so far.
These two pics show another plug and box just like the 10 in the set. I already had this single in my collection, and has no connection to the set I just bought. It shows the same markings and the same plug ??
I found a Model A spark plug to compare the "fire ring" plug to. Its not even close. The Model A plugs are 7/8-18 tpi
I tested the "fire ring" plug in a Model T head. The threads just fall into the hole and are a "sloppy fit" (hillbilly technical term). So they obviously do not fit a Model T
I did not have a metric thread gauge, but the thread count/pitch of the "fire ring" plug is between 16tpi and 18tpi. so I assume it has Metric threads. I measured the outside diameter of the threads to be 0.705.
That only leaves V-8 Ford and the early "letter" series cars, if these are to fit some Ford product. Maybe someone knows what the size of the V-8 plug or the "letter" series plugs are ?????
I think Dale is correct about them being motorcycle or aviation plugs.
Possibly there were several sets that were labeled wrong back in the day. That may be the reason of these surviving in their original boxes. Some dealer may have just stuck them on the top shelf and forgot about them when he found out they were incorrect and had no market to sell them to . ????
These may be super rare, but I probably will never know for sure what they fit. They do look nice with the other spark plugs I have. (I really do not collect spark plugs. But that was another discussion on another thread)
Thanks for all the comments ....
Yikes, I MEANT to say model As had 7/8-18, not 18mm.
BUT these are still probably 18mm. If theyre not 1/2 or 3/4 NPT, or 7/8, then I think you only have metric sizes (18, 14, 12 and 10mm)left.
Where's Terry Bond when you need him?
Just for fun, take one to your local parts store and tell them you need the exact same plug, X 8!
I'm here! I was away in PA for the AACA Grand National meet in Greensburg. Got to see some nice T's there too.
Yes, those Bethleham plugs are 18mm. Don't know why they were in boxes marked 1/2 Ford. Probably war-time stuff and the plugs most likely are aviation. Quantities of these surfaced years ago at the Carlisle and Hershey swap meets so they are not a rare item. Makes a nice display in your garage though. The "5-point" shown is an earlier plug.
Terry, thanks for the info. They will still look nice on the shelf. Being in the incorrect boxes will make for a good story. Thanks again everyone ...
I wish to clarify something.
In my previous post,that should read
"......neither one half inch pipe thread or seven eights eighteen threads per inch"
Where all that gibberish came from,I'll never understand.