Hoping to tap the vast knowledge base here. Why is it that when one needs new threads in a stripped out hole or to create a new threaded hole, that one can't just drill larger and tap in new threads? I have used a heli-coil on a manifold as recommended and it worked out reasonably well but I'm curious about this. And obviously I have very limited experience in this area.

I'm not an expert, so if you get a better answer believe that.

However the principle reason I can think of is that a larger bolt might not fit through the hole of what you are mating to the surface. Typically the holes on the other thing are not much larger than the bolt, otherwise it will move around a lot. Think of a manifold getting mated to a head. Strip the hole in the head and the hole in the manifold might not let a bigger bolt go through.

Thanks, that makes sense. The heli-coil lets you use the original size specified bolt.

Plus if the part needs to be torqued to spec that is not going to happen with a different diameter bolt. The helicoil will also give you more wear resistant threads.