So putting aside the Austro Daimler SLE that sort of frustrated me a bit...I moved onto my rare bird, the MBK (Motobecane) Atlantique that I have found 0...zero...nada...zip information on. Trying to get a decently durable headset on it since it is presumably an Xcross/hybrid/gravel grinder type bike.

I measured 40mm of stack height available, and do not mind adding spacers on. It seems to be JIS, which means 30.0 inside diameter, 27.0 crown race and presumably English threading for a 25.4 steerer. Sir Sheldon says that these were common on lower level Asian bikes, but this one is definitely made in France. Is that unusual?

I do not feel confident making the crown race 26.4...

--I am a fan of Tange, but the Passage and Levin are too short and I do not wish to cut the steerer (I would rather add spacers, or am looking for 38.0 stack).
--I have seen several BMX headsets that fit the profile; is there any difference in BMX headsets?

Options on the bay
--Fits the profile but looks rickety https://www.ebay.com/itm/27107848551...Bk9SR9Dy55eHYQ
--A black Levin with BMX specs? https://www.ebay.com/itm/19544725761...3ABFBMho3OmIdh
--What I WISH would fit (26.4 crown race) https://www.ebay.com/itm/27453493760...Bk9SR4iNzpiHYQ

YST hybrid? https://www.ebay.com/itm/30372486636...Bk9SR9S7gpmHYQ

OEM headsets from old Japanese bicycles were made in various styles and heights, might be sourced from someone's discarded/unwanted frame or bike.

I thought of that. Even with my treasure trove of unused bicycle giveaway frames and parts, most of what I have left is proprietary or threadless or 1 1/8"

Perhaps a Stronglight roller bearing headset would work for you.

I’m having a tough time finding the specs on all of the different ones. I actually have one, but I think it might be missing one piece. I should check for sure.

The attached is from TangeSeiki web site.

Seems to show that crowns are available for 27.0, (see red dots). The site shows the availability of 27.0 crown for the Levin CDS in the same manner.
Not sure of easy availability of this version or if the crown in 27.0 can be purchased separately.
.

Not much help; The FSA and Origin8 are 40 mm stack, the Richey Logic is 36.5 mm.

Per the late Sheldon Brown's headset dimension cribsheet, some French headsets indeed had a 27.0mm crown race.

However, going the JIS route has one potential "gotcha". Also per the late Sheldon Brown's headset dimension crib sheet French and JIS headsets have a slightly different frame cup OD - 30.0mm for JIS, and 30.2mm for French (same as ISO/English/Italian). Can't say for sure that this will "bite" you or not. But it conceivably could; JIS cups might fit a bit too loose in your frame.

However, some recent Tange 1" JIS headsets I've seen listed appear to have ISO cups (I recently bought a JIS Passage that did). Not sure if all do, however.

FWIW: the Tange Falcon 250C is indeed available from a couple of overseas vendors on eBay in JIS spec (27.0mm) in chrome, but apparently not in black. But I couldn't find cup specs listed for their offerings on either vendor's site.

JIS crown races are indeed available separately for the Tange Passage and Levin CDS 1" headsets. I've read that they're interchangeable (within the same model, Passage or Levin CDS) w/o problems.

https://www.universalcycles.com/shop...s.php?id=49908

Safest bet might be to go with an ISO-spec Tange Levin CDS and purchase a separate JIS crown race for it, then add spacers. That combo should theoretically work (ISO cups, JIS 27.0mm crown race). But I haven't tried it personally.

Apparently I anticipated this quandary...and my overbuying paid off. I had created a box for this build which I found and lookee here...I could have sworn I tested the locknut but none to be found, so I ordered one and some 2mm spacers. I guarantee I will find the locknut now.

Are you planning on replacing just the lower part of the existing headset, or the whole thing? If the latter, you may run into problems.

I'd recommend trying the upper adjustable cup on the existing fork's threads very carefully before installing anything - or getting and using a thread pitch gauge on the threaded portion of the steerer. If it seems to start but binds quickly, you may have an issue with using the Tange upper headset.

According to Sheldon's headset dimension cribsheet (I linked it in my earlier post), there's a chance that you may have a French headset with a 27.0mm crown race (apparently French headsets were made with both 26.5mm and 27.0mm crown races). If so, the fork may be metric thread (25.0mm x 1mm) vice 1" x 24 TPI. JIS upper headset threading is 1" x 24TPI.

Per the same cribsheet, most French steerers have a flat instead of a groove for a keyed washer. However, I don't know if that's universally true - or just almost always true. I'd still test either way, preferably with a thread pitch gauge.

If it turns out you have a French headset with a 27.0mm crown race, you can still use the Tange lower if the lower cup fits your existing head tube tightly enough. But I don't think you'll be able to use the upper part if your steerer is French threaded without replacing the fork.

Edited to Add: Since it appears your Atlantique is from the 1990s, I guess it's possible it used an Asian-made, JIS-spec fork vice one made in France to French specifications (lots of European firms were apparently outsourcing frame work to Asia during that era). If so, it may have been originally built with a JIS headset vice a French headset. Hopefully that turns out to be the case.

Good quality JIS headsets here: https://www.njs-export.com/collections/headsets

Truth.

I know I had it and put it down after testing the threads.

it is definitely English/standard threading. Probably because it was after France had joined the band.

Well Dawg,
My co-op over bought on these last year perhaps it is what you want.

all the parts

All the specs

And the price is right
Lemme know. MH

Thanks MH. I appreciate the looking. Needs 30.0 cups. I now have the headset which was in a box I set aside for the build that I forgot I had.

I test the locknut. Check. A little crunchy. So cleaned the threads. Greased it up and tried the adjustable cup. Went on smoothly.

Put the headset back in the box and misplaced the lock it somehow. What the crap. Bought spacers and a new locknut. I expect to find the old locknut in some random place I put it down.

$12 for my sins of stupidity. But the spacers should look decent enough...oddly the black headset has a silver keyed washer...not sure why.

So $23 for use with a $28 headset! Plus I ordered stuff I didn’t need carelessly.

Anybody need headsets?

Hmm. ​​​​​jdawginsc this is the one I mentioned to you offline…just got upstate and checked my bin. It’s your size and even though I snagged this in a shop in Brooklyn it seems like its from the same source as MH’s. Small world indeed. Yours for the asking, as long as you’re over 12 years of age.

Thanks! I’m going to try the black on with spacers first. If it fails, that’s the size.

of course then I will have to buy silver spacers...or purple ones.