Hey all,

I went to replace my top cap with something nicer and I noticed that the expander plug screw was very loose and high up.

Should I screw this back down?

I didn't loosen the stem before changing the cap as I thought this was fine to do, did I pull the screw up because of this?

The top cap acts as a washer of sorts, so without it it's not surprising the bolt is loose since it is not screwing down against any resistance. Also, many top caps are domed, so I'm not sure how it can be determined to be "too high" without a top cap in place.

Get the new top cap, install it and go from there.

Edit:. Once you get the headset preload set (the primary role of the plug) and the stem correctly tightened, the star nut/compression plug really doesn't have a mechanical role in actual use (although the plug helps to protect a carbon steerer from stem clamping damage).

I just assume the nut should be tight In the plug? I read it needed to be 9nm. Maybe I'm getting confused

Let's say if I loosened my stem and the preload is released and I needed pre load everything again, should the plug screw be tightened first? Before the top cap is screwed onto it?
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If the stem is loosened, then everything has to be readjusted, but a top cap is required as the adjustment process is essentially pressing the stem and headset components together to get the correct bearing preload. Without the bolt AND top cap there's nothing to compress the stem into the headset.

Obviously the plug screw is the first one tightened as the top cap screw threads into it and pulls everything together. Your explander/plug screw is basically falling out of the expander. Tighten it to the spec'd torque then put the top cap and screw on and adjust the headset. It constantly amazes me how confusing headsets are to so many people.
And once again this post should be in 'bicycle mechanics' NOT general discussion. C'mon people.

That's exactly what I needed. Do I need to loosen the stem to tighten down the plug screw or can I do it while the stem is tight?

You need to loosen the stem. If it's tight it will actually squeeze the steerer tube onto the expander and it won't move.

That's what I get for posting while taking Percocet, sorry to the OP for misreading the original post and answering a question that wasn't asked...

One more thing, when removing a stem. I've seen lots of videos and some loosen the top cap before the stem bolts and some loosen the stem bolts. Does it make a difference?

Makes no difference. If you understand how threadless works you'd get it. I generally undo the stem bolts first, then the fork won't fall out of the bike if I let go of it.

I had to do-undo the headset about 3 times...until I understood how a threadless works. 😉