The quick and dirty method is to blacksmith the shell smaller. Three well placed whacks with a hammer at the shell's edge will set that spot further in. Three means all three will communicate with the cup. Well placed keeps the cup relatively centered. I like to use a chisel, dull but better able to focus and place with.


It's not uncommon for these soft steel shells to distort bigger over time, hard use and neglect. I've repaired a few dozen this way over the years. I can't remember anyone returning with a problem and I have worked on a few of these again later and have seen the fix keep. One aspect to this repair is that a 1 piece crank sandwiches the cups against the shell. With a 3 piece crank the cups have room to move outward before hitting the arms.


The problem with shims is that if the shell is distorted where do you shim to? Shims really like a lot of contact surface area and no movement between the parts. Otherwise they tend to walk about, so to speak.


The three adapters I've installed all were bolted together with long bolts running through the shell side to side. First one did come loose and needed revisiting with. Since I run the bolts really tight and thought about thread locker (which I dislike using on the common bike sized bolts in general).


I'd love to check out an image of the adapter cups. Andy