Originally Posted by CrawfordGene
There was and probably still is a solution to bad threads—it usually happened from cross threaded spark plugs in the softer metal of aluminum heads. It's a heliocoil, perhaps spelled right. Never used one, never saw one, almost have cross threaded plugs, but not quite. Sounds like something screwed into the hole and it opens and grabs it and provides a new thread for the plugs. Sure would like to see that Ford with plugs flying through the hood though.
s have been around for decades. We used them when I worked in a machine shop to make repairs to non-critical pieces in the production process. That was thirty years ago.
The work piece (cylinder head) has to be accessible enough to drill, tap, and thread the coil into the hole, The coil is stainless. I have heard they work very well for this, but have never used it.
The usual method to try to prevent blow-outs is to re-torque the plugs every 40,000 to 50,000 miles. I have read where people have gone through and pulled every plug, check it for gap, etc., coated the threads with a product to help prevent seize-up, and re-torque them at the chosen interval, replace them at the second interval, if all were good before.
Many folks do not realize that threads must be clean, dry, and in the case of aluminum/steel connections must be coated with at least a light film of oil, if not an anti-seize compound otherwise there may be thread tearing and definitely you will not get a true torque reading.
I believe I remember there was a special "anti-seize" recommended for the steel/aluminum contact made by the plugs, which would be different from a steel/steel connection elsewhere.
Just stuff to remember.