I am just finishing up building a bike with a 1" threadless headset (first bike I've built with a non-threaded headset, so sorry if this is a dumb question!). There's a very small gap between the stem and headset, about 2mm (picture attached). I need a spacer there, right? If so, if anyone has a 2mm spacer for a 1" fork... I'll pay you to mail it to me! And separately, how important is the size - should I overshoot or undershoot? Thanks!

-Colin

If there's a 2mm gap, you'll actually need a 4 or 5 mm spacer.

overshoot, put a spacer of 3mm or make one from a pipe, or grind a spacer to 3mm (so 1mm to have the stem above the end of the fork tube, so the locknut can pull between the frame-lower crown-steerer tube and stem-spacer-upper headset-frame that is the force transmission when tightening the bolt. So leave 1-3mm of clearence between top of the stem and top of the steerer tube (steerer tube should be recessed into the stem) and cut to dimension a spacer

Go to any bike shop. They all have a box of spacers in a variety of thicknesses, diameters (1" and 1-1/8") and, sometimes colors.

3~4mm would be a safe bet.

get 1mm and 2x 2mm spacers.

I"m almost sure I have a bunch of these and will give you a few. Remember that the stack has to be enough to being the top of the stem above the top of the fork so the top cap can press the stem down without bottoming on the fork.

email me your address directly at fb@"the site under my signature below" & I'll drop a few into the mail. The cost is 1 beer (not a Bud) & I'll collect if I'm ever in your neck o' the woods.

Great guys, thanks for the tips. I should have mentioned though, that I'm using a 1" fork with a 1 1/8" stem, so there's a shim in there. I think this makes things a bit more complicated, because the shim is 2mm longer than the stem (which is what my first post showed), AND is about 2mm longer than the distance between the top of the headset and the top of the steer tube. So, when I tighten the top cap, the shim DOES press down on the headset, but there is still the gap I showed because the stem is shorter than the shim. Does this mean that I should/need to get 1 1/8" spacers to fill the gap, or do I even need to get spacers for the shim (these would be 1")? Sorry if this is confusing, I've attached a picture of the top cap tightened on the shim, and a picture of the shim/steer tube without the top cap. Thanks again for all your help,

-Colin

Unless you can find thickwalled 1" spacers with an OD well over 1-1/8", you're better off using 1-1/8" spacers with the shim pushed down into them to keep them centered. Otherwise the stem will tend to climb over the 1" ones and not compress the headset properly. If your stem shim is taller than the stem, you might use 1" spacers or do without them and have the top cap cam compress the headset via the shim, with the stem clamped in a neutral position, neither top nor bottom.

Sweet, so since my shim is taller than my shem, and tall enough to compress the headset, I can just do without spacers and use the shim as the compressor? Does it look like my shim is tall enough (it's maybe 1 or 2 mm taller)?

-Colin

If I were desperate to race it within 15 minutes, I would probably cut the shim and steerer to make it work without a trip to the shop.

But it's your bike. And cutting things down unnecessarily isn't smart. The shim is probably long enough and there are a bunch of ways to make it work. But I would advise you to install it flange-down, put a 4 or 5mm 1 1/8" spacer over it, then install the stem. (Or stem, followed by spacer, for a slightly lower position.) That way you've got something broad bearing against the top of the headset. Your top-cap bears on the stem itself, and you're not using a thin-walled part to do the job of compressing the headset. Spacers are cheap and easy to find.

Yes, you can use your setup as-is -- adding spacers would be done for cosmetic reasons only. However, I agree with Metzinger's suggestion to flip the shim, install a 5mm spacer and put your stem on top. This would both provide a proper bearing surface against your headset, and would be visually appealing. As several other posters have mentioned, you can go into any bike shop and pick up a 5mm shim, they might charge you a dollar or they might just give it to you, depends on the shop and whether they know you.

Sweet guys, thanks for the tips.

-Colin