I have blown a plug out of the head for the second time on my Mod motor.  i recently read an article (can't remember where)that showed an expanding tap that allows rethreading from the "bottom" up.  Who makes it and who sells it? Don't want to go the helicoil route if I can help it.  Tiremon60  

Below is a link to the Mac Tools site with what you are looking for.  They arnen't cheap but your head is more expensive.  Don't skimp here!!  http://www.mactools.com/portal/site/mactools/menuitem.6c9db894a3743751f735c110f070c3a0/?vgnextoid=6b0552850014d010VgnVCM100000426fa8c0RCRD&vgnextfmt=default