any options short of a machine shop, heilicoil, loc-tite?
spark plug blew out of head on 1990 Mazda Miata MX-5
Yes, I have had a lot of luck with a product called Thread Cert ( I believe this is how it is spelled ) It is much more robust and sturdy than a helicoil. Be sure that you have the skill to drill out and re-thread your spark plug hole, because you only get 1 chance. The next step is usually a new head, if the re-threading does not go well.