Replacing Shower Arm
I am in the process of replacing a 30-year old shower arm. I had some trouble breaking the old one loose but some oil and a little time with a pipe wrench got it started. When I pulled it out, it looked like some of it had broken off inside the pipe in the wall. Fortunately, after a few minutes with some tweezers, I was able to get all loose pieces out. So far so good, I think.
Unfortunately, I ran into trouble when I tried to screw the new shower arm into the pipe inside the wall. I think I am getting the new arm aligned, but I cannot get the threads to bite. Obviously, it is impossible to get any visual confirmation since the pipe is inside the wall and behind some tile. Feeling around the threads with a finger suggests that everything is fine, with no obvious damage. This leads me to think that perhaps the just the start of the threads of pipe are bent or somehow constricted and preventing the shower arm threads from biting.
Does anyone have any experience with this? Or any thoughts of a way to get the threads working again, using a tool for instance?