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Michael,I just checked the data sheets for JB Weld. The data sheets show it contains both steel and carbon black particles. I could not find any information about the insulation (conductivity) properties of the material. I would be cautious when using JB Weld to make spark plugs.It may be OK to bond the tungsten electrode into the macor insulation, but make sure there is no JB Weld exposed at the ends. You can wipe off any excess with acetone. I think you should ensure there is absoluty no JB Weld between the central electrode and the earthed outer body. otherwise there is the risk of tracking when the high spark voltage is applied.Mike
Mike i had the same concerns, but they write on their Homepage jb weld is an Isolator https://www.jbweld.com/pages/faqsSo i gave it a try on my first set of plugs. There was no Problem withe the jb weld but with the corian that was eaten away by the sparks.Nevertheless i will Keep the jbWeld in the smal chamber between the the two Isolator parts. Just to be sure.Michael