Originally Posted by
Camilo
Once you tighten the stem bolts, the top cap serves no purpose. You can't tighten the bearings by tightening it, and the bearings won't loosen if you loosen it. You could actually remove it without any problem. It doesn't matter if it's tight. Snug it up if it works a bit loose but no need to go overboard.
Provided that your stem sits slightly below the top of the steerer tube, you can definitely remove the top cap and star nut after tightening the stem. I did that on quite a few of my kids' bikes with no ill effects.