I've replaced the J-bar of one of my Esterbrook J pens with an 54mm aftermarker J-bar. After doing that I noticed that the lever is loose. While the pen otherwise worked, the rattle of the lever annoyed me enough to pull the pen apart again and try to fix it.
Googling for the issue revealed some insight from Brian Anderson here.
If the J bar is a replacement aftermarket bar, then you would need to remove it and file down the sides to make it flush with the inside of the barrel.
However I haven't found any information about how best to do this.
So I thought I would try on my own and grabbed a couple of pliers and used that to flatten the metal on sides of the J-bar. However it didn't give easily, and I'm not sure if it helped at all. I still can't insert the J-bar in a way in which the lever isn't loose. On one occasion I almost succeeded, but after trying to use the lever 2 or 3 times, it returned to being loose once again.
I must admit, I have no idea how to do this properly. Could somebody help with some advice, please?