The fact the focus helicoid separated into 2 pieces is because the focus ring (once it comes loose) allows this to happen. When focus ring is loose and shifts position or is retigtened in the wrong position, it will allow the two focus halves to focus out too far and become disengaged. It can be rebuilt but helicoid has like 6 individual starting points, only one is rights and as you screw it back in, it will hit the edges of the helicoid "keys" in the back and prevent you from turning all the way down. Once taken apart this way, most parts in the back have to come out to start the rebuild. Then infinity focus has to be reset or lens will do the same thing next time it is focused out. There should be a 1/16th" BB for the clicks, tiny spring may be missing too. John