threadless stem adapter question
 

I have a specialized stem and fsa bars that I got practically for free that I want to put on a bike with a quill stem. The way I was thinking about doing it is not even using the locknut and just putting on the threaded top race, a spacer that will cover the threads and then the adapter with the stem on it to hold the spacer in place and keep the threaded race from backing off. I just think it will make the bike look cleaner, but is it a bad idea, or will I look like an idiot? lol.
I can take a picture if I didnt explain it well enough.

You have a threaded headset and you want to use a threadless stem.. Have I got that right?

Is this the adapter you are talking about?

http://www.performancebike.com/shop/...tegory_ID=5230

If so, I would highly recommend you use the locknut. Just use the adapter as it was meant to be used and mount your stem accordingly. I had one of these adapters on an older bike and it looked clean to me. Remember... Function takes priority over form.

bad idea.

you need at least 2 screws binding into each other to make them hold their position on a moving axis.

your idea will just result in a loose headset that will, at best make you lose a bearing, at worst result in a bent frame or fork.

It seems dangerous to me (if I understood correctly).

Also, I think that it will be very difficult to adjust the preload of the bearings that way (by tightening the quill stem screw).

If you fancy the idea of having a wobbling fork and loose headset, feel free. The locknut (I'm assuming you mean the locking headset ring that follows the threaded race) is the element that holds the race when rotational force is applied. The threadless top cap/star-nut assembly is what applies clamping force to the threadless assembly, within which the stem is sandwiched.
This said, there is a threaded-to-threadless adaptor commercially available for just such an occasion. Make sure of the stem's clamp diameter as well.

Just buy a quill adaptor, mount the stem on it and call it a day.
Reality = Hardly anyone but you cares what your bike looks like.

I just did this to my bike, but the stem is too long. I have a shorter quill that I think I'll use and just "let it be what it is" instead of buying more stuff. But yes, it sort of looks different and more modern and you don't have to rewrap the handlebars everytime you want to change stems, but then again, once you have the right fit, you don't need to change anything else.