I've not yet ridden it much, but I've noticed that the stem on the Schwinn Traveler that I converted to a fixed-gear, rocks side-to-side when torque on the bars while sprinting or climbing out of the saddle. The quill stem is one of those old, smaller-diameter ones - 21.15mm or 0.833" quill width (Typical quill stems for 1" steere tubes are 22.2mm; the old Schwinns and some other bikes have the 1" outer diameter of the steerer tube, but the tubing walls are thicker so the interior diameter is 21.15mm instead of 22.2mm.) I've tried raising and lowering the quill stem, tightening the bolt really tight, etc., and no change - the stem still rocks back and forth slightly but noticeably.
I've got another Schwinn with the same dimension steerer tube and quill stem, so I swapped the stems back and forth to isolate the problem: stem or bike?
Turns out the machined angle at the bottom of the quill stem, the part that contacts against the wedge which tightens to hold the stem in the steerer tube, is machined at a slightly wrong angle, so that the bottom of the wedge contacts the quill, but the top of the wedge is set a bit away from the quill. The stem that doesn't rock, from the other bike, has the angle machined such that the wedge is flush against the bottom of the quill over its whole contact area. And I made sure that both wedges are exactly the same dimension, and I even switched them back and forth between the stems. The problem is entirely with the aluminum part of the quill stem from the Traveler. Here are some pictures.
Also, here are two shots of the stems when the quill is loosened a bit. Angle and contact stay the same in both instances.
It appears that the original machining on the bad stem was done at a slightly wrong angle.
I don't know what to do here. I can't swap the good stem out for the bad one, because the bad one is 10cm extension and the good one is 8cm, and I want the longer extension.
Here are my options:
1. machine the quill to the optimal angle. This is doable, though tricky, but I don't have the tools. I assume a belt sander would work best? Could a bike shop do this for me?
2. buy a new stem. Only, stems in 21.15mm quill are very hard to find, especially with a long (10 or 11cm extension). The old SR stems come up on eBay every now and then, but usually the seller doesn't realize that they are for a smaller dimemsion, and I need to figure that out from pictures. Even so, the ones that come up are usually 8cm, not 10 or 11cm. There is a local bike co-op of sorts, and they may have something. Bike shop may have something in a bin, too.
3. sand down a 22.2mm quill stem. This is a lot, though, removing 0.5mm of quill width all the way around. Would take a long time Probably safe, as the old SR stems at 21.15mm appear to be identical to the SR stems for 22.2mm, but the 21.15 were simply machined down narrower - there's a nice little ridge where the narrower part starts.
4. ream the steerer tube out to 22.2mm internal diameter so it accepts regular quill stems. Since the outer diameter of the steerer tube is normal 1", I assume that this would be okay and not unsafe - the dimensions would end up as that of a typical fork. However, it may be difficult to do, and/or expensive.
Any feedback is appreciated. Thanks.