I would like to use a modern 1 1/8" stem on my old lugged frame using the matching lugged fork. I haven't used a quill stem adapter before because most of the time, it looks kind of clunky because the shape of the lock nut. If i use a quill stem adapter on a threaded fork do I need the lock nut on the top of the headset? My plan is to use the adjustable race and washer from the headset, install the adapter and use a 1 1/8" headset spacer to bridge the gap between the stem and the washer. I would think this would put pressure on the adjustable race to keep the headset properly adjusted. Is this a fool's errand?

You are not changing the function of the headset by using a quill-to-threadless adapter. So, yes, you must use the entire headset including top nut.

Here's a pic of bike of mine with an adapter.

Theoretically, it should work but I haven't tried it. It's sounds like it's going to be tedious to set the proper bearing preload.

Colonel, fine work there, as usual. What cable hanger is that? It looks much nicer than what I normally see or use.

I understand how they are supposed to work (adapter fits in the fork just like the quill so the functionality of the headset doesn't need to change) but I was wondering if the lock nut becomes expendable if you have something else putting pressure on the adjustable race to keep the proper bearing adjustment. My adapter doesn't have the flaring portion at the base of the stem so my thought was to have a spacer (1 1/8th threadless)run from the bottom of the stem to the top of the adjustable race. My adapter has about 1/4" taller stack height than the stem so the spacer should stay anchored. I am thinking about doing this for cosmetic reasons only, but wanted to make sure that it would work.

I was thinking that too. That's my main concern.

I think I saw this setup in a schwinn circuit in the retro with STI thread. I'll try to PM the poster.

I follow what you're trying to do now, but I don't think a spacer is a functional substitute for a threaded locknut. You need to think very small. The locknut pushes its own threads upwards while pushing the adjustable cup's threads downwards. That opposition is what keeps everything locked tight. A spacer just won't do the same thing.

I see. So you plan on setting the headset tightness by pushing the quill adapter down just right and tightening it? I suppose it might work, but I don't think I'd choose to do it that way.

Thanks. It's something I cobbled together myself. That's a cable hanger that hangs from the seat post binder bolt and one of those elbows that comes with a hanger that clamps to a quill stem. I think I had to file the elbow to fit it into the brass piece.

Back in the 1970s there was a common Japanese headset that used two locknuts. The lower locknut looked like a ~3/16" chromed spacer with three notchs for a hook spanner. This might be cosmetically tolerable while providing greater ease of set-up. You may be able to find one at an older LBS.

that's a good suggestion T-mar. Most adapters I have seen are tapered, you'll have to find a straight one and use a stem shim for this to work and look more seemless I think. I think that if you use a straight adapter with a shim you can put a spacer between the stem and lock-nut and it will look more better also. I think that trying to eliminate the lock-nut will be difficult since you will have to bascially weight the adapter while you tighten it and that will be hard since you tighten it from the top.

I'll see if I can find a picture of that setup. That sound like it may be more along the lines of what I am looking for.

I would almost have to over tighten the adjustable race, install the adapter (with 1 1/8" spacer and stem) tight on the race and then loosen up the race.

I am with the Colonel and everyone else on this you need a locknut. I have used several quill adapters and never saw (but never really looked) for a way to get around using a locknut. Plus in away it really takes away a main advantage of the whole set up, being able to quickly and easily change the stem length ot stem height without alot of other adjustments.

that would probably work, might take a few tries to get it just right, but it should work just fine actually.

I'm going to play around with it over the weekend to see if I can get it adjusted correctly. If not, I'll just leave the damn lock nut on there! Thanks everyone.

make sure you wear your helmet and pay your insurance premium.

I suppose over time due to vibration it could slowly loosen, but you would notice long before something happens.

I believe that as you steer the bike, the top race will want to unthread itself. It always does, that's why the top nut has to be so tight to keep everything in place. The finely threaded upper race has a mechanical advantage over the devices that try to keep it from backing off. The equally fine threaded top can do the job but I don't think the stem clamp can stay tight enough to do it. I doubt you will have any kind of catastrophic failure but you will find yourself tightening everything down very often. Possibly after every ride. I admit this is only a guess since I haven't tried this so let us know how it turns out.

Wont work.

I wouldn't worry too much about catastrophic failure, but you might want to keep a couple extra headsets on hand.

I was playing around with it last night and got it adjusted without much difficulty but won't get a chance to ride it until the weekend. I would think that if the quill adapter is appropriately tightened and the stem is securely fastened on the adapter, there would be nowhere for the race to go. I'm not worried about catastrophic failure, I think some people have a flair for the dramatic. I got a response back from the guy who posted in the retro with STI thread (a very sweet schwinn peleton) who confirmed he has been running this setup without issues for a few thousand miles.

I figured it would work but thought it might be tedious to set-up, taking several tries to get the pre-load correct. Glad to hear it worked out relatively easiliy.

Ideally, for this set-up, you need a quill adapter with a recessed expander bolt so that a star nut could be installed above it and you could load the stem and spacer as per a theadless system. If a thick spacer could be manufactured to seat where the adapter changes diameter, this would allow for a recessed expansion bolt. The problem is finding an expansion bolt with a small enough drive recess to allow the allen key to pass though a standard star nut. This would require about a 4mm recess.

Getting it adjusted as you said I would think would be no big deal. Keeping it adjusted will probably be a different story.

If the OP got it set properly by backing off the headest tightly against the spacer, it should maintain adjustment as it were a threaded headset with locknut. The only issue is that any further adjustments to the stem may affect the headset adjustment.