I replaced my stem today, but it seems the new one doesn't take up as much room on the tube as the old one, so I have about a 1/8 space of exposed metal. I suppose it is mostly a cosmetic thing, and probably helps protect it from the elements in bad weather; but do they sell very small spacers. Right now, the stem is sitting on top of all of the standard (3/8"?) spacers; with about 1/8 inch between the top of the stem and the top cap (don't know the technical term for that thing).

Should I try to find a set of small spacers to fill that area? Or is it not a big deal?

Spacers on threadless headsets aren't cosmetic. Without the proper spacers, you can't load the bearings on the headset properly and the headset will loosen. Headset spacers come in a variety of thicknesses from 20mm to 3mm. You need about 3mm of space between the top of the stem and the stem cap to properly load the bearings.

It's a big deal. A loose headset is easily damaged and may have to be replaced. Don't let a $3 part cost you much more than that.

if i'm understanding the situation correctly (and i may not), you've managed to assemble the stem/headset correctly and are left with a gap between the top of the stem and the cap, such that the steerer tube is exposed.

spacers above the stem and the stem cap itself are essentially assembly tools. IME, a stem can be fitted correctly without their use. OTOH, if you are inexperienced installing a stem and adjusting a headset without the use of a stem cap and the proper length of spacer(s), if needed, above the stem, it might be a good idea to double check that the stem/headset is adjusted correctly.

so, as stated, if correctly adjusted, you don't really need anything more. in fact, you don't need the cap either. but stem spacers are readily available online. aluminum or carbon. google "headset spacer".

You are understanding my description correctly, but my other online research over the last hour has led me to believe that cyclo-commute is correct...the design of a thread-less stem set-up is such that the top cap compresses the stem and spacers together to tighten up the whole thing.

So, while it IS possible that I may be able to press the stem down pretty tight, and then tighten it so that the stearing tube is held in place enough to function, it is not really the way it is designed to work, and could lead to failure.

Thanks.

huey is theoretically correct that headset adjustment can be done without using the top cap and spacers for compression but it's an unreliable technique. cyccommute is "more right:" as reliably and properly setting the headset adjustment is far better done using the top cap and bolt working on stacked spacers. As long as there is a 3 mm or so gap so the top of the steerer is below either the top of the stem or the top of a spacer above the stem adjustment is easy.

Like the stem where it is , height-wise? add a spacer on top of the stem and the cap goes on top of it.

you press the headset down , into preload adjustment from the top thru the stack of spacers & the loose stem.

but the spacer-stem stack has to be higher than the steerer tube itself. so the cap does not bottom out on the steerer tube before the headset is in proper Preload.



Putting a QBP Problem Solvers' Locking Spacer on first , directly above the upper race. holds the adjustment and the fork wont fall out,

while you move the stack of spacers and stem over it .. Integrated headset was kept together that way..