Gap in headset dust cover--what am I missing?

Question

I replaced my stem with one that has a taller stack height. I learned about proper gaps for the headset preload and had to requisition a thinner spacer to ensure there's ~3mm between the top of the steerer and the stem spacers. (I initially had the top cap too far from the top of the stem and did a 10 mile trail ride like that)

After installing the thinner spacer and torquing everything down, I noticed the dust cover/top cap of the headset bearings has a gap. It's flush on the front of the bike and ~3mm uncovered on the back. I disassembled it, cleaned out all the muck, and put it back together (tightening the top bolt first, then adjusting the stem position, then final torquing the stem bolts), but can't figure out why the bearing and split-ring washer thing don't go into the head tube far enough for the dust cover to be flush with the frame. The teen at the bike shop said sometimes you have to tap them in with a hammer. Is this correct?

There's no binding I can feel, but the front occasionally feels like it wanders on my test drives--like the stem/steerer connection is too loose. I can't tell if this is all in my head, or if the bearing slightly protruding from the headtube is indeed the culprit.

When I got the bike this spring, the headset/head tube made a ton of creaking and groaning, which was solved by disassembling and greasing everything with Park's PPL-1 lube. I've learned a lot more about bikes maintenance since then, but don't remember having any leftover parts after reassembly!

What have I done wrong? I can't find any 2020 Specialized Rockhopper parts diagrams to confirm whether a spacer or something is missing. The bearings pretty obviously only fit in one way, same for the split ring guys on the top and bottom. But maybe I have a compression ring upside down?

Answer 1

I think the answer is that the Range stem needs spacers with an outside diameter small enough to fit inside the "shelf" ridge inset into the top and bottom of the stem (the depression that Andrew noted in his comment). This shelf is perpendicular to the steerer axis, not sloped, so any spacers properly seated on it will be flat and flush. This also means that at least one spacer is required beneath the stem, as it looks like the headset top on the Rockhopper will not seat properly in that shelf.

Here's a view of the PNW Range stem I found online that clearly shows the shelf:

Just for reference, here's a promo photo of the stock Rockhopper 2020 from Specialized:

If you click to open the image and zoom in, you can see that the headset top is flush with the headtube top, and the spacers above that along with the stem all seem to be flat and flush. This is consistent with Criggie's observation that the OP's bike photos show a stem with curved bottom and top surfaces, which suggests the root of the problem.