New to this site so if this isn't the right forum go easy on me. Recently bought a early 70s World Finest Bicycle by Sekine. I'd never heard of Sekine before this purchase but fo $40 it looked like an interesting project. Brooks saddle, dia comp and sun tour components etc. Question is about a Sun Tour "Quick Pattern" clamp that was on the stem above the upper bearing cup and below two spacers and the brake cable guide. Looks like a quick release seat post clamp but I found it on the stem. Was this originally supposed to be on the stem or was someone before me using it as a spacer? If supposed to be on the stem, what's its purpose?

short answer: I don't know what the clamp is for.

longer, better(?) answer:
I bought one of those Sekines back in the 70's, and it had one of those stem QR gadgets too! I had the bike for a year or two, but never figured out what it was supposed to be for. It seemed like a lot of extra steel on a bike that was otherwise reasonably light. Removing the QR would require some sort of spacer to be inserted in its place, if memory serves. I suppose you could cut the steerer tube shorter too.
I hope someone out there knows the purpose of this odd quick release. This weird little detail has haunted me since the mid 1970's (well, maybe not "haunted", but nagged at me)

Steve in Peoria

I had the exact same question with the Sekine that I bought at a thrift store. All I can think is it was a way to raise and lower the stem quickly, but that seemed a little sketchy to me.

Well that helps knowing that others have seen the same clamp on the stem. Now to figure out what it's for. I also thought it could be to adjust the height or even swivel the handle bars for storage but seems odd. Thanks everyone!

There is a system for clamping the stem in a steerer tube where the tube has a pair of cuts in it, one vertical but not extending up quite as far at the top of the tube, the other horizontal-but-angled so that the tube essentially has a pair of ears cut out of it; the clamp squeezes these together and grips the stem.

You still need a top-nut to set and keep the headset adjustment.

Here's a pic of one on a bike (yes I know the stem has a standard wedge, belt-and-braces here):

No more speculation permitted until someone posts a pic of this curiosity!

Now let me break my own rule... my first thought was the previous owner repurposed a seatpost clamp as a kludgey lock ring mechanism for the headset. I have something called a Gorilla Lock on an old mountain bike that keeps the headset from loosening. Actually very effective although it should be completely unnecessary. The fact that other Sekine owners have seen this same doodad pretty much debunks my notion. Interested in learning what it does.

In this thread:

I've Done Some Research, but I Still Need Help!: Japanese Sekine?

you can see examples of the clamp in question - and if you squint at the remnant of the photo of the pink frame you can see the horizontal slit in the head tube.

I can corroborate that this device was intended to provide tool-free adjustments for handlebar stems and seat posts. Generally seen on folding bicycles, it was originally offered in 5 diameters and catalogued by SunTour through the 1970s, being phased out circa 1984, though by the end it was offered only in two larger sizes, appropriate for seat tubes.

Interesting. Thanks everyone for the interest and feedback!

Looks like a quick-release version of the old Brit headclip: