Sorry If Im a novice at explaining this . So I have tri/road bike I have not ridden much in a couple of years. Prior to riding it recently I knew something wasn't right with the headset, its kinda a long story. So when you ride there is play in the headset area especially when braking. Like I said there is more to it but I'll get to today when I took it apart for inspection. I noticed the top headset bearing has some kinda of insert to tighten it up around the fork but the lower one did not and I tried to switch them the upper one would not sit down where the lower one sits in the correct spot if I used the upper up with the insert. I sat up about an inch higher. In the photos I included for people to see, I took the lower bearing and put it up top to show there is quite a gap meaning its way bigger that the fork tube . Can anyone explain whats going on here ?

Here I am showing the lower bearing up top so I could photograph it . And you can see its quite larger then the forker steer tube .

check the bearings for ANY loose or Rough feeling While Off of the bike... if they are smooth and not loose, Put Them Back On as you found them... if there is any roughness found, i advise a new headset, complete, since it will have Fresh seals and a new wedge ring too.
Only the TOP bearing uses the centering ring wedge.. the bottom bearing seats onto a chamfer at the fork crown, centering it well.

it may be that all you needed was to slightly adjust the headset preload tension... there are a lot of vids on How to adjust Modern threadless headsets on Youtube.
it's very simple to do, and only takes a matter of a few minutes... watching the vid will take longer!

PS.. is that a Carbon fiber steerer tube?... if so, USE A LOW TORQUE RANGE TORQUE WRENCH to avoid damaging the Carbon fiber, or you'll be buying a new fork.
the proper torque spec. should be on the stem clamp, or listed on the fork... if not, FIND THAT SPEC. ONLINE Before torquing those clamp screws, ok?

The lower bearing should have the tapered face downwards, and locate on a conical seat on the fork crown. Then the upper bearing has the tapered face upwards and is centered with the split conical ring before you add spacers and the stem.

Hi ,thank you for the reply. It is definitely not the preload tension thing , I repeat it is not. I had thought that before and replaced it twice.

Right exactly, but something isn't right. Im thinking maybe I was sold the wrong inside diameter lower headset bearing.

FSA, Cane Creek, and Aheadset maintain a large list of application-specific Headsets for most recently manufactured bikes... you may want to look up your bike and verify which headset bearing sizes are correct for your bike... the headset bearings, unfortunately, get sold online with rather generic and un-detailed info at times... calling them a 42mm when they really measure 41.7mm, etc.
and then, there are press fit tolerances involved, too...
i know.. it bugs me too.
it is what it is...

so... no tapered wedgie for the bottom bearing, it goes on with the inner chamfer facing down, and the wedgie is for the top of the top bearing, and it's inner chamfer faces up.
Watch The Vids on Threadless Headset adjustment.
and don't skip the careful small torque wrench use.
Crushed CF turns to an expensive, more flexible, piece of garbage.also.. consider that TWO sizes are in play on the fit to your bike... the frame is an INTERGRATED headset design... both bearings need to fit nicely in those head tube bores too....

If I had a nickel for every time a DIYer declared "it's not that" when it was exactly that....
There is nothing to buy when setting the preload of an Aheadset.

Ilovemyride ,
You seem to be asking why the bottom bearing does not fit the steerer of the fork.

It is correct that t bottom bearing does not fit the fork steerer tube, it is not meant to fit.

At the bottom of the steerer there should be a “crown”, it is a taper, often a metal washer or a taper in the carbon, with a taper that narrows at the top.
As the lower bearing is forced down onto this taper (crown), it centers the fork. Notice the lower bearing is also tapered on the bottom to match the taper on the fork.

Hope that helps

Barry

Here give thi a try.

I watched the vid. It appears I have the ZS zero stack and yes everything is identical in place. Ugh.

Does the top of your steerer tube sit slightly below the top of the stem or spacer on top of the stem? There needs to be a gap to allow the top cap to compress everything together when tightening the bolt to set pre-load.

Im pretty certain it is because that was a thought from before. But I will check again tomorrow. Im trying to think back when it all of a sudden was loose for seemingly no reason but maybe I changed a spacer and wasn't paying attention, I would definitely do something silly like that .

Sometimes adding a thin spacer above the stem can solve that.

Tapered headsets with a 1.5” bottom bearing and 1 1/8th top bearing are common. Suspect yours is this.

Yes there is the necessary gap to hold it tight. But I discovered I think that the expansion plug is causing a issue. Should the bolt here in this picture rotate on its own, if so it is stuck ?

The fork crown is the part that connects the legs to the steerer (with most unicrown forks the crown is reduced to a sleeve fitted over the steerer, although there are a few unicrown forks with a lugged crown).
The part of the crown where the headset crown race fits is the crown race seat, conical on some forks, a cylindrical interference fit on others.

Is this top bolt supposed to turn freely from the bottom ?

The top cap bolt in the pic might be two separate fasteners. You can see "and were asking about" how the bolt turns everything. Try to undo the bottom larger diameter threads from the top allen head bolt. The larger bolt may have its own Allen head and is hollow with inner threads which is used to set the plug solidly in the steerer on it's own so that the smaller top bolt can have something to anchor to when setting preload. You may just not have been able to put enough torque on the top bolt due to the slipping expansion plug in the steerer. I'm not positive that this is how your setup works but possibly.

Thats exactly what I was thinking. If I recall ( I've had this bike a looooong time ) the bolts seize from sweat. I dabbed some oil in there last night maybe find some plyers and a towel and twist.

For another reason I was thinking the expansion plug is too long for this application.

**** UPDATE **** FIXED !
So a while back I thought I had a problem with the compression nut or something and exchanged for one of the bigger ones. Not sure it was not good for my set up, but I decided to purchase a small compression nut just after these posts and made sure that top bolt was not seized in the top cap any longer and WOW , I heard all the pieces pop and pull together as it was being tightened like someone said on here should be . I went for a 40 mile ride , nice and strong no loosening! Yeay, so happy! Thank you !

Please use F&F if you send my nickel via PayPal....

Instead of playing 21 questions, a good shop mechanic who can actually see how this headset was assembled could have this diagnosed in ten minutes. Fixing it could take longer, depending on parts. Is the split wedge washer correctly in place directly on top of the top bearing?

He’s already fixed it

I see it now. #19. Miraculous.

Thanks.