The dispised chain idler
I assume most of you with China Girl tiddlers despise that infamous idler as much as I do. Here is my solution before I clean it up with rounded corners etc. so it is easier to understand. I started with sections of bed frame because it is thin and strong. I replaced the roller bolt with a 5/16" carriage bolt and milled half through one of the ells to share the square neck with the bracket and the slot the roller bolt runs in. The bolt head was reduced to 5/8" as that is what the diameter of my center-cutting end mill was. This will allow tightening the damned bolt from the backside only. The adjusting bolt is a 2-1/2" X 5/16" total threaded one. It is anchored with a nut and the adjustment is done with the 2 nuts on the anchor ell. I shortened one leg on one leg to make adjusting range and used a square file to make room for the bolt square.