seibaatgung

I just installed a new stem, but removing a spacer left a little free space at the top.

Crankycrank

Yes, In your case it won't put any preload on the bearings without the proper spacer on top. This video is a little long but explains how a threadless headset works.

seibaatgung

As in I can't rike my bike like this or shouldn't do so for too far?

Crankycrank

No, don't ride it. It will sort of function OK meaning it will steer and not fall apart but you could do some damage to the bearings/headset or worse in a short time. You mentioned removing a spacer which if it's the right thickness you could add it on top of the stem for a correct setup. Watch the video to understand it.

dsbrantjr

You need a spacer so that the top cap can bear upon the spacer/stem combination in order to adjust the preload of the headset bearings. As it is, the topo cap is bearing on the steerer and not the stem/spacer, so the bearings cannot be correctly adjusted..

seibaatgung

I previously posted about it and was advised to take the spacer off - it's too tall. https://www.bikeforums.net/bicycle-m...-too-tall.html

Rolla

Both of these threads are giving you correct advice. In the earlier one, the stem's top fixing bolt was above the steering tube, and thus needed to be lowered by removing the spacer that was underneath the stem.

In the current iteration, the steering tube extends above the stem and thus requires a spacer so that the top cap doesn't bottom out on the top of the steering tube.

Like this:



Another way to do it would be to put a thinner spacer under the stem, so that the bolt isn't above the steering tube, and there's a gap between the top of the stem (with no spacer above it) and the top of the steering tube., like this:

Pop N Wood

I'm confused. The top cap doesn't really do anything once the headset bearing is adjusted correctly and the stem locked in place. All I use the top cap for is to set the headset tension before torqueing down the top cap to lock it in. At that point all the cap is doing is preventing water and dirt from entering the top of the steering tube. One can remove it and ride normally.

In the OP's case one has to wonder if the headset is properly adjusted, especially since the picture of the cap seems to show the steerer tube is crooked.

Why are all of you knowledgeable guys saying there has to be a certain spacing on the top cap?

Crankycrank

If you're confused watch the video in post #2 or one of the many videos and tutorials on threadless setup. It's very simple once you understand the function of the top cap preload, spacers and clamping the stem. OP says in another thread he was advised to remove a spacer from below his stem, OK, fine no problem except that if you remove a spacer from below the stem you have to move it to above the stem to maintain the proper spacing for the preload cap to work or cut the steerer tube (not the best solution in this case).

Rolla

Because if the top cap is just sitting on the top of the steering tube, it won't "pull" the steering tube up and "push" the stem down, so it won't properly load the headset.

The functionality of the top cap after it's been installed is irrelevant.

I wouldn't make that diagnosis based on that photo, and even if the steerer tube was cut an an angle it will still function just fine as long as there's a gap between the top of the steerer and the top of the stem. The top cap doesn't interact with the steerer tube; it interacts with the top of the stem (or a spacer).

Pop N Wood

Thanks for the video but I've never had an issue adjusting a threadless headset.

What confused me is why the spacers matter once the headset is properly adjusted. I think Rolla phrased the problem more clearly than I did, without the spacer/stem protruding above the fork tube it is hard to get the proper pretension.

jccaclimber

That's the main point. The cap is needed to get the tension set the first time. However, at that point you are also relying on the stem to have enough clamp to hold preload. This is usually true, but the loads the headset experiences when you hit a pothole/large bump are much higher*, and in those brief instants the top cap still being tight is often what prevents your headset from getting loose over time. Forks that have a slipping star nut as well as forks that have cheap expansion plug top caps/star nut replacements tend to develop this issue over time, even when the stem has been torqued to spec. The telltale sign is that the spacers between the stem and upper headset get loose. If those aren't as tight as the day you installed it, it's because the headset is losing preload.

*Yes, a lot of this is straight in line with the steer tube, which doesn't matter, but any off axis load coming in from the wheel or the handlebars tends to put a side load on the bearings, which through the tapered contact will result in an axial load trying to loosen them.

alo

Under normal circumstances, it is impossible to get the proper pretension.

alo

Wrong. They can come loose, and are likely to come loose.

DorkDisk

When aheadsets first came out, the rule of thumb was to leave a 3mm gap at the top for the cap to seat into. Without the gap, the cap does not seat properly. Fast forward to today and crabon steerers that require compression caps at a certain location, the 3mm gap is no longer welcome so we add a 5mm spacer on a flush steerer for the cap to seat onto.