We’ve all been there. You’re tightening a bolt into a threaded hole and it’s a bit harder than usual, and then the whole thing goes loose like the metal threads turned to cream cheese. Oops. You’ve cross threaded, over-tightened, or simply stripped the threads right out of the hole. That’s a big oops. Fear not, it’s possible, if not super convenient, to fix it. But what’s the best method? You’ve probably heard of the options. You can drill and re-tap, you can drill and helicoil, you can drill and time-sert, or you can just say fuck it and slather some JB Weld into the hole. Which one is going to hold?
Listen, I’m not going to say that it’s pretty easy to tell which of these methods is best from the outset, but it’s pretty obvious to tell that JB Weld ain’t it, chief. I’ve used JB Weld a number of times in a pinch, but never for something that actually needed to secure itself to another part with a bolt. JB says it can be drilled and tapped, but I don’t trust it, and after this video, that mistrust is for valid reason.
After that, you’ve got tapping the metal and helicoil, which are effectively the same level of good. Timeserts will work if you’re in a pinch, and will definitely hold the recommended level of torque for at least the size tested, but if you need the extra level of self assurance, maybe avoid it.
Here’s one piece of advice I have to add, and it’s not a proven fact, so take it with a grain of salt. Ari mentions that there’s no way to keep metal shavings out of a cylinder when cutting threads on something like a spark plug hole. I have a way to do it if you’re in a pinch and desperate. For something like a motorcycle, it might just be easier to remove the cylinder head, but that’s a really involved job on most automobiles, so here we go. Put the cylinder in question at bottom dead center and fill the cylinder with shaving cream. That way when you cut the threads and inevitably leave shavings in the cylinder, you can then slowly push the piston upward, shoving the shaving cream out the spark plug hole and taking the metal shavings with it. Boom! Fixed.
I also appreciate that Mr. Ari Henning goes into the difference between a thread chaser and a thread tap. I’ve definitely used a tap to clean up threads before, but having seen this I will be ordering a set of thread chasers. The last thing I want to do while cleaning up my mess is make it worse.
All of this is pretty good advice (except maybe for the dodgy advice I added in), so take it and learn from it. You will be a better wrench for having seen this. Bless Ari and The Shop Manual.