Mystery solved on "loose" stem/steerer with an Innicycle.
Background: My 3rd or 4th Innicycle adapter, installed on an '88 Ironman, had an issue: No matter how tight the stem was tightened, it still seemed to move on the steerer. @
joejack951 and I discussed it, and I tried 3 or 4 stems, all which pivoted on the steerer. JoeJack really wanted to inspect the stems and the Innicycle adapter, but I did not really want to go down that rabbit hole.
In what I thought was "the end," I bought a serious stem, Easton EC90. No way should that have been able to slip. It did. Dammit.
I went back into the instructions, both written and in various posts re: the Innicycle. it came down to "pre-load."
In the instructions, during installation you use a stem sort of as a "handle" to tighten down the headset pre-load, then you remove the stem, add spacers as needed, and then bolt the stem into place and use it like any other.
Because I'd never read the instruction, I was using a channel-locks to tighten down the pre-load. (JoeJack heartily disapproved of that). Well, the channel-locks simply don't have the grip and the torque capability to get the pre-load strong enough. When I added spacers and bolted on the stem, it wasn't slipping on the steerer; the steerer itself was moving because the pre-load was not enough to lock it in place.
It was moving, not the stem.
the light bulb moment: I was riding the Ironman on the rollers this morning. Not a time to have a loose pre-load imitating a loose stem. I was disgusted, so I stopped Zwift and pulled the bike into another room, pulled the bars, pulled the stem, re-installed the stem and tightened that damn pre-load into place. Then I re-installed the spacers (all Innicycle-great spacers) and the stem, and the bars and the Garmin mount, and got back on the rollers and did 2 x 1-hour sessions, on the rollers.
So now I have 4 different stems, all of which were thought to be too big or had some defect. One stem was destroyed by over-tightening (stripped out the threads).
And sore legs.
The Innicycle remains, in my opinion, the best bike frame component to be developed in the last 15 years. Sure, replaceable dropouts are great, but the Innicycle works on old bikes, can breath new life into obsolete frames, and puts the flexibility and variability of modern stems to older bike fit. It would have saved 1" threaded forks, singlehandedly, just a few years earlier.