I have a head with some interesting spark plugs.
Bad news is the porcelain is broken. Is there some place that remakes the porcelain insert?
Here is the business end.
Is it worth saving?
Looks like the firing end of an Edison 13?
If you just want something that will run with the dual ground electrode shell that you have, you can remove the cracked porcelain and substitute another of similar dimensions (doesn't have to be the same brand). Replacement porcelains sometimes show up on Ebay, although I don't see many right now.
You could also remove your cracked porcelain, glue it together so that it is in one piece, and post a picture of it in the classifieds, or take it to Hershey as an example of what you are looking for.
BTW, here are a couple of pics of an Edison 13. The second pic is a side-by-side with an Edison 14 single ground electrode plug.
As crazy as this sounds, I helped a high school friend with the professional restoration of an early 1908 KNOX. It had 4 cylinders, overhead valves and pressured mains. It also had a dual ignition with 2 plugs per cylinder. I built up all new repro coil box for it and made the coils for that part and timed the restored high tension magneto with a linkage that advanced both ignition systems simultaneously. It was a very sophisticated car and way outside my usual venture but Dave Lewis (R.I.P.) was a good high school friend so I said OK I will see what I can do for you. He found 7 plugs but the 8th one had a broken porcelain. I was stumped but he said "I have glued them together and they were running OK when the cars left here..." So he got out his epoxy and ... the engine would run on either set of plugs with either ignition on separately and even together. It ran perfectly. I have no idea what the compression was but I would have said - no way. Then again I have seen air bubbles big time coming from the threads of a T spark plug hole that had filled with water during a cloudburst and the engine seemed to be running just fine. Just telling the truth here. Don't ask me how long it ran that way. I didn't want to be there when it quit.
Was your friend the same Prof.David Lewis that appeared in several Ford documentaries ??
I don't think my Dave Lewis appeared in any documentaries. He was well known as a premier restorer of BUICK's mainly from the 30's. He took on this 1908 Knox because his best Buick customer asked him to. He called me to ask for help because he knew I played with early brass cars at that time. My Dave Lewis operated his shop in Springfield, IL which is my home town. His restored cars were breathtaking.
If you use epoxy for repair don't use any with a metallic filler. The best ones I could suggest are 3M 2214 Non Metallic Filled (heat cured) or Armstrong A-2 ( room temp or heat cure). It's possible a readily available clear epoxy would be just fine.
Sorry A-2 and 2214 are ferociously expensive.
Are the copper asbestos gaskets still available, or is there a supply of originals?
No. If there's a source I haven't found it. I use these airplane parts.
They fit under the insulator, but unfortunately won't fit over the top on most plugs.