Hello fellow forum mates,

Building up a tiny trek for my tiny friend and I've hit a snag. I can't seem to get the stem past the min. insertion mark. I've checked the steer tube and it looks clear. Not sure where to go from here. Any suggestions are appreciated. I've attached pictures of the front in question. In one picture you'll see a scrap stem bolt I've inserted to give you an idea, and yes, I know the bolt is crooked, that's why it's scrap . The problem occurs with non-crooked stems too. Thanks in advance BF.

Are there burrs or imperfections inside the steerer tube? Can't really tell from those pics.
Does the stem have a burr or imperfections?
Is the stem one of those ultra-long ones like the Technomic?

A possible, perhaps most likely, explanation is that the steerer tube was deformed by someone over-tightening a stem.

Or are you trying to insert a 22.2 stem into a 22.0 fork and it sort of goes in partway?

Maybe, due to the relatively short length, you're running into the butt? Typically, you do not trim steerers from the butted end but sometimes you have to with shorter lengths to get adequate stem engagement. This one looks long enough that you shouldn't run into that problem but maybe this brand has an abnormally long butt?

Between my own bikes (54 cm frames generally don't have long steerer tubes) and my daughters' even smaller bikes, my experience leads me to believe this is the likeliest explanation. If it's a butted tube, the stem's probably not gonna go in much past the minimum insertion depth.

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...once you are satisfied that the problem is related to some sort of interference between the steerer tube and the stem exterior, it's usually possible to get more insertion depth by using sandpaper on the alloy stem to reduce it incrementally where it needs to be smaller.

as a short bicycle rider: you're probably running into a deformation above the brake hole, bur or otherwise. if not that, i have had a few frames where the tube tapers. however, i don't know if steerer tubes were ever butted (even if they were, you would be going from thick-thin-thick, so it should fit. try fitting the quill stem upside down, to check for roundness?

Can you tell if you are getting the expander below the threaded section of the steerer? If so you are probably OK. If you need the stem to be shorter you may need to cut it, in which case a) you may need a shorter expander bolt, or more threads on the one you have, then shorten it; b) if you cut a stem you should give it a new insertion line or at least indicate that the original line is not to be trusted.

From Sheldon:

Note: Steerers are butted at the bottom, so the hole in the steerer is constant-diameter until near the bottom, then the walls taper inward in the butted section.It is vitally important that the steerer extender (or stem) is not inserted so far that the wedge is installed where the steerer is narrowing, or it could come loose unpredictably. When this happens, only the edge/corner of the quill or wedge contacts the steerer, and it is trying to "grab" a slanted surface.This is sometimes a problem on smaller frames if you try to insert the stem or a stem riser too far down into the steerer.The stem also loosen unexpectedly if the steerer has been bulged out by overtightening the expander or wedge.

T-Mar has probably nailed the problem.

Sheldon Brown addressed this:



Sheldon Brown's Bicycle Glossary W



But what's the stem you're trying to use? The kind with a conical expander are particularly badly suited to short steerer tubes. You may have better luck with a wedge.

Another thought - deformation is usually caused by over tightening the stem; which makes the steerer tube *expand*. that sometimes makes it harder to get the fork out of the frame (DAMHIK), but should actually make it easier to get the quill in the steerer.

So I am thinking wrong size stem (ie too large), friction from rust in the steerer tube, or burrs on the stem.

Best to measure the stem OD and steerer ID with a decent micrometer to eliminate the first issue, then I would clean up both the stem and the inside of the steerer tube and try again. Don't forget anti-seize.

Thanks for the responses everyone! I believe I'm running into the butted section of the tube. I suppose I'll need a find a shorter stem. The current stem I'm using is nothing special, an origin 8 stem that came from the donor bike. The bike I'm building up is our own @fender1's tiny Trek seen here:

https://www.bikeforums.net/classic-vi...set-100-a.html

Ive had success cutting some off the bottom of the quill using a Dremel cutting tool. If you cut too much off then you might need a new bolt.

I see screws or rivets from the headbadge inside the tube.

Hey! I know that frame. If it would help, I can send the stem and shim that I used. The stem was one of those .833 diameter Schwinn stems. I never ran into the tube butting problem as I never used anything but this .883 as it was short in reach 80mm and that was what my son needed at the time. Let me know.

I was just about to mention the same thing.

Well, maybe not use the "abnormally long butt" comment. Seems kinda personal.

Hey, I recognize that persian rug!

Stem no like Fork?

Fork Smash!!!

As T-Mar and rhm suggest, the fork steerer is so short on that small frame the bottom of the stem is probably running into the butt taper before clearing the minimum insertion line. Here's a typical steerer tube from Nova showing the length of the butt (50mm) and the length of the butt taper (30mm). That's a total of 80mm from the bottom of the steerer tube (even with the bottom of the fork crown) and the beginning of the taper. On a very short head tube frame, some of the steerer would typically be cut off at the butt end to provide room for the quill stem to be inserted at least to the minimum insertion line.

Yes please!

Hehe

Hey, it's not like I said abnormally wide butt or abnormally big butt.

What if you used a threadless adapter? It won't get style points, but you could "slam the stem" easily enough at that point.

Edit: Or maybe not. I've never used on before.