Steering Tube Came Up Out of the Fork about an Inch...

[Tophat Fiddle]

Hello, folks. I was riding around yesterday and as I was braking to a stop, I sort of pulled on the handlebars as I was straightening up from the recline and the steering tube pulled up and out of the Fork, making a horrible screeching noise, and then as I stopped, my weight came down on the handlebars and it went right back in. It all happened so fast, I'm not 100% sure that's what happened, but I think it did. The bike rides and steers perfectly fine as far as I can tell, and the steering tube seems to be secure in the fork. The photo shows it after the tube went back in. Is this something I should be concerned about? Thanks!

 

[IyhelM]

Not 100% sure how a Q45 stem is made but there should be no possibility of movement between any of those parts once it is set in position - from the fork tube up to the beam.

 

[kizarmynot]

Do you have spacers and a top cap installed? These work to keep the fork from moving up and down.

 

[Tophat Fiddle]

Do you have spacers and a top cap installed? These work to keep the fork from moving up and down.

No, I took those off when I cut down the stem. I guess I'll put them back on, heh! Thanks!

 

[Tophat Fiddle]

Not 100% sure how a Q45 stem is made but there should be no possibility of movement between any of those parts once it is set in position - from the fork tube up to the beam.

Thanks! It happened so fast and I wasn't really looking at that at the time...maybe it was something else and I imagined it. Hmm....

 

[CruzRider]

You also need a top cap on that steerer tube. You are risking serous injury without it.

 

[Boreen bimbler]

Slightly off topic sorry. You can actually remove the top cap after you've compressed everything and tightened the stem properly. We used to have to do that to run our front cables through the steerer tube when BMX's first used a-headsets. The top cap is really just to pre load the headset and I certainly wouldn't rely on a star bolt version for safety in any way.

 

[Tophat Fiddle]

You also need a top cap on that steerer tube. You are risking serous injury without it.

The top cap I pulled off doesn't do anything, it's just a little thing that covers up the hole. It doesn't connect to anything. I'll post a photo....

 

[Tophat Fiddle]

You also need a top cap on that steerer tube. You are risking serous injury without it.

Okay, here's a photo of the end of the stem that I cut off (first photo). See the insert there? The bolt goes through the top cap and then tightens into those threads in the star insert. Flipping it over, (second photo) we see that the bolt doesn't do anything other than hold the top cap on. The bolt's not long enough to fasten into anything past the star nut, even if there were something under it. I didn't take the star nut out because I couldn't get it out. It looks to me that the star nut simply provides a threaded hole for the bolt that's holding the top cap on to thread into. I suppose that's to keep rain or debris from getting into the tube. But I don't see how that affects safety....

 

[kizarmynot]

You may want to check out YT for additional information. In general, you add spacers so that the top cap is no longer flush with the top of the steerer tube (fork), then tighten the bolt into the star nut, then tighten the stem (not sure what it's called for a CB) to keep that from rotating. This should also keep the spacers in place. As @Boreen bimbler noted the top cap can be removed, although I've never done that. The top cap is needed if you have spacers above the stem (some DF bikes), but it may not be a concern for a CB.

 

[Mathew Fy]

I don't recommend relying on the fork tube clamp alone. (Doing so may result in loss of steering as you almost had.) It's designed to be part of the system with the fork, bearings, spacers, clamp, star nut, and stem cap. With the fork/pivot clamp loose, you preload the bearings to a just-tight-enough setting, then re-tighten the clamp.
I searched and found you can buy star nut + stem cap combos with a hole to allow a cable to go through the fork and exit just above the tire, if you have enough room that is.
BTW I followed Ratz's directions to slam my V20 stem. https://forum.cruzbike.com/threads/vendetta-v20-build-diary-2016.10189/page-2#post-118807
Also, you might like Robert's Q45 assembly video:

 

[Boreen bimbler]

I did post a park tools video explaining the headsets on the previous post regarding this. They are pretty simple to do once you know.
As for taking off the top cap. It's what we had to do in the early/mid 90's before they made some BMX topcaps with an extra hole for the cable like I have on my flatland bike now. Also, the 1" to 11/8" converters dont use caps and rely on the stem clamp so it is a proven safe thing in both those cases. It's only needed to pre load the bearings and hold it there until the stem is tight. Unless you have a carbon steerer where you should use a bung that reaches below the stem to stop you possibly crushing the tube. Obviously it looks tidier to have a nice top cap so no reason to take it off.

 

[Robert Holler]

If you cut down the steer tube you must reinstall a NEW star nut in the top of the fork. The cap is 100% essential as without the cap and proper spacers you cannot set the headset tension. The purpose of the star nut is to allow the "pull down" leverage of the cap to the spacers.

Order of tightening: Top Cap to set headset, THEN the side bolts of the clamp. Then snug down the top cap bolt just a bit.

Please please please please - x 10,000 - before riding another yard, get a new star nut in there so the cap can be replaced for proper headset tension. Also if you did a big cut down of the steerer and need more/proper length spacers, and LBS should be able to provide those. The spacers and cap are what keep that tension proper and the two pivot bolt clamps are what keep it tight to the steerer tube.

Typically when cutting down a steer tube (our bikes or any bike for that matter) the usual practice is to either replace the nut after the cut. Also note you can not remove a star nut to be re-used - they are a one-time deal. You can also use a very long M6 bolt to carefully tap with a hammer the existing star nut further into the tube until it is about 15-20 mm below the surface of the cut line.

Also, the length of the steer tube needs to be such that the spacer stack plus clamp when all set onto the fork steerer leaves about 3-4mm (but not more) of a recess below the surface of the clamp. This is to allow for a bit of space for the headset compression for proper adjustment. If there is too little gap the top cap can bottom out on the steerer. If there is too much gap the top part of the clamp is clamping nothing at all. This is absolutely critical.

Robert

 

[Greg S]

I'll echo and amplify what @Robert Holler said: get a new star nut and install the fork properly. Those spacers aren't for decoration, they perform an important function. It is possible to install the fork correctly without spacers providing it's cut to the correct length but this is definitely one of those "measure twice, cut once" things since getting it wrong (cutting too short) means you're off to buy a new fork.

Here are the steps:

- put however many spacers you want to use plus the stem on the bike
- mark the fork at the top of the stem
- cut the fork 3mm below your mark. Careful is key here, I'll say it again: measure twice, cut once
- install a new star nut (or, if you have the proper tool, use it to push down the existing one) 15-20mm below the cut
- install the spacers and stem. Put the top cap on and thread the M6 bolt into the star nut. Tighten to 6Nm. This will preload the bearings
- align the stem with the front wheel. Tighten the stem bolts (5-6Nm)

You could at this point remove the top cap but why? Once everything is put back together, you should be able to hold the front brake tightly, rock the bike back and forth and there should be no play at the headset.

I also note from your picture that the top of the steerer isn't cut very cleanly. Although you can probably leave it like that it'll mean that in order to get the requisite 3mm below the top of the stem you'll need more spacers than if it were cut cleanly. If you don't have a proper guide you can use a clamp tightened around the steerer as a guide. Alternatively you could file the steerer level.

As Robert said: "please, please, please, please x 10,000 - before riding another yard..." do it properly. The best thing that will happen if you continue to ride it like it is is that it will destroy the bearings or damage the steerer tube in the frame, the worst thing that might happen is the top headset bearing will pop out of the steerer tube and you'll crash.

Be safe, do it right.

 

[CruzRider]

As Robert said: "please, please, please, please x 10,000 - before riding another yard..." do it properly. The best thing that will happen if you continue to ride it like it is is that it will destroy the bearings or damage the steerer tube in the frame, the worst thing that might happen is the top headset bearing will pop out of the steerer tube and you'll crash.

I never knew there were opinions on both sides of the top cap. I am generally a play it safe kind of guy. Especially, when I hear such pleas from Robert himself and Greg. The bicycle is a deceptively simple machine.

@Tophat Fiddle safe riding. We enjoy your videos!

 

[Boreen bimbler]

The main reason I said about top caps was because they should not be relied on for safety. I have overtightened them many years ago before I properly knew how it all worked and it's not that difficult to pull the star nut up (and ruin it). They are basically just a pre load bolt. And obviously tidy things up nicely. Sorry if there was any confusion.

 

[Robert Holler]

I have zero clue why someone would not want a top cap, or in the case of a CF fork a plug.

 

[Boreen bimbler]

I have zero clue why someone would not want a top cap, or in the case of a CF fork a plug.

It's what we had to do to run the front brake cable through the steerer when they first used A-headsets on BMX in the early 90's. Not really applicable otherwise.