Look at the links in the first post. There is one known ss# near yours marked as a Professional with some details.

My apologies. I must’ve missed that. I’ll go look. Thanks for the guidance!

It’s not a 5000
 

So, from looking at some Sekai 5000 images, it certainly doesn’t look the same.
Since there doesn’t appear to a way to discern the model from the SN, and components seem to vary (mine has a Levin headset), are there “standard” frame angle specs listed somewhere? I assume that would be the best way to figure it out.

https://people.ece.ubc.ca/~gillies/s...3_02_02_07.jpg

https://people.ece.ubc.ca/~gillies/s...3_02_02_07.jpg

https://people.ece.ubc.ca/~gillies/s...3_02_02_07.jpg

😂 Well, my last post failed and I’m not going to rewrite it. I’m too old to remember what I wrote, so I’ll nickel and dime my way to “ten.”
The important part of the message was “Thank you!”
I do remember that much.

I worked for Sekai in the late 70s, during the period when they brought in the 5000s. Very few were brought in while I was there. Maybe 10. Here's some pics I took at Lloyd Tamura's last shop a couple years ago just before he closed for good. Lloyd and his brothers started their bike shops Velocipede and Pine Street Cycle in the late 60s. Started Sekai in 1971, partnering with Shinwa Trading Co. The 4000 and 5000 frames were built by a small shop called Miki. If you had a 5000 you would know it. They were very light. I doubt they brought in any after I left in 1979. The company was pretty much on the ropes by then. They'd had to turn over management to Norco of Canada at the request of Shinwa.

https://cimg5.ibsrv.net/gimg/bikefor...2023637a6b.jpg
https://cimg1.ibsrv.net/gimg/bikefor...f872936d7a.jpg

Becky Twigg had a 5000 track bike. I chatted with her about it at Marymoor one day.

Rebecca (nobody called her Becky) only rode for them a couple years. They really didn't do anything for her career. I used to pick her up and take her to races in those days and work on her bikes. Then we both switched to Rainbow Cycling Club in late 1979, with Mike Kolin as our coach. That's when she started to blossom. Mike got Schwinn to make her some Paramounts. It was after the Chicago cage had closed up, but before PDG was really fired up, but somehow Mark Muller pulled it off.
Here she is when I saw her last at Jerry Baker's memorial 11 years ago. She's 62 now!
https://cimg4.ibsrv.net/gimg/bikefor...b8639d5faf.jpg
https://cimg6.ibsrv.net/gimg/bikefor...9888880042.jpg
https://cimg7.ibsrv.net/gimg/bikefor...a63fe194bd.png
https://cimg1.ibsrv.net/gimg/bikefor...c709f22416.jpg
https://cimg2.ibsrv.net/gimg/bikefor...6c1ad040e3.jpg

Wow!
 

That’s great stuff! I lived in Madison and rode a Sekai 2000 in ‘79-‘80 before it was stolen. My dad was fairly tight with the Yellow Jersey folks, so I’d occasionally get to hang out by them at the races around the capitol building (“The Square”). Every once in awhile I’d see a Sekai in the field and get excited.
I’m certain at this point that it’s not a 5000. Unless I’ve gotten it wrong, it’s a Mikko built in the first half of March, 1978.
In your extensive experience, have you found any “pattern” or significance to any of the last four digits of the Serial#?

Dropouts
 

And another thing… I have yet to see a Sekai frame with these dropouts, so I think it’s been modified. There are no adjustment set screws (or holes to receive them),and it looks like they must’ve cut off the fender/rack eyelets. The frame lugs have rounded triangle cutouts as well, where I’ve seen others have diamond cutouts.

There’s a picture of a 4000 Professional “Track” bike that looks exactly like mine; same color, same frame lugs with the triangle cutouts, on Rendezvous. The obvious difference being the track setup.
My frame has cable guides.
The forks are different.
The rear dropouts are different.
Cyclone 12 speed
I believe this is where I originally got the idea that it’s a 4000 Professional. Seems logical, but logic doesn’t make it so.
It was originally purchased through Champaign Cycle Company.

Absolutely correct me if I am wrong here but weren't the 4000's and 5000's sold as framesets rather than complete bikes?

Yes, imported and sold as framesets only. The first complete bike in the Sekai line was the 2700. Called the 2700 GT-Deluxe (maybe Glen Tamura named it after himself?) Same frame as 2500 but with slightly better parts. Here's a catalog from after my time there, in the 80s, the Norco years. The 2500 had disappeared by then, as had the 1500 and 400. And they had added BMX frames and some even cheaper models. Shows a 4000 built up but that was only for the catalog. I'm sure Norco would not have sold one built up either.

Vintage Early 80's Sekai Bicycle Catalog Road Bikes & BMX Frames | #3863072440

Here's a web site someone put together using information from me.

Sekai Bikes - Classic Japanese Bicycles
Bob Freeman

You mind if I add the classic link to the first post for this thread?

Not my link so go for it.

Ah!
 

That’s great to know. And I can’t believe I missed that in the miles of info I was reading! It certainly makes sense to me. Thanks all. A couple more posts, and I think I can add pics. Then whomever can decide if they want to add it to the list or not. Diligence done. 🙂

I just assumed the Zeus brakes were replacements. I guess they “could” be original, but the levers don’t match, sooo…

I’ll be doing some of my own replacing shortly anyway.

I just went back in the thread and noticed what Alberto is calling a Georgina Terry style frame. It's really a Bill Boston style frame, for he pioneered the 24" front wheel design in the mid-70s. Many companies borrowed the design in the 80s. We sold some from Centurion, likely built in the same shop as the Sekais. I saw this one Bill Boston built at TOSRV-West in Missoula in 1976. Can't find a pic of it at the moment but here is a bit about it from Bill Boston himself.

Those bikes with small front wheels

In late 1974, a friend called asking to stop by. He and his girl friend were in college in Montana. Alice had been having problems riding a Gitane mixte on their club rides. She was a good rider but, at 100 lbs, was at a big disadvantage pedaling a 40-pound bike up hills. They were hoping I could build Alice something lighter so she could ride at the front of the pack.

When they arrived at the shop, I was surprised to see that Alice was barely over 5 feet tall. I knew immediately that this was going to be a major design challenge. We used my road bike and a stack of blocks to establish a maximum stand-over height of 28 inches. And, observing Alice on her bike, I quickly saw that the effective top tube length was far in excess of what she needed.

Then we worked at deriving a top tube length that was appropriate. If memory serves, we used a spare set of bars, which Alice held while sitting on my bike. As Ted held up the bike, Alice moved the bars trying to find a position that felt and looked right. Then I measured how far the loose bars were behind the fixed ones on the bike. From that we decided a 19 inch top tube with an 8 cm stem would be good.

We discussed crank length and decided to try shorter ones than the 170 mm length that she was using. We agreed that 155 mm would be a good starting point and that we could adjust the gearing downward to compensate for the loss in leverage. We believed Alice would be able to increase her cadence more than enough to maintain the speeds she was used to. However, I knew I still had many problems to solve and told them that I would call in a couple of days when I had some solutions.

The biggest problem was to get the top tube lower than 30 inches from the ground, which is the lowest that can be built while maintaining a head tube. I decided to make a scale drawing of the bike – something I had not done in years.

Ok, I know, you are asking yourselves how could I build bikes for more than two years without making drawings. The answer was simple. When I started building bikes, some hot new technology arrived from Hewlett Packard in the form of a scientific calculator. With that I could make faster calculations and get more accurate dimensions than I could by hand.

Back to the story. I laid out the bottom bracket, the seat tube, the top tube, and a line to represent the head tube. I kept looking at the drawing and finally realized there was no way I was going to get a 27 inch wheel in there. Even if I played around with the head tube angle and rake, there just was not enough room for toe clip clearance (of course now it would just be pedal clearance). Suddenly, I knew how Archimedes felt when his bathtub overflowed. I had been trying to make the bike and rider fit the components. Clearly that was not going to work.

After taking more measurements, I found I did have sufficient room for a 24 inch wheel in the front. I cleaned up the drawing and excitedly called Alice and Ted and told them that I had a solution I thought would work.

At first Alice was disconcerted with the design, as she thought two different wheel sizes would look strange. And you know, some people still have that criticism today of Georgena Terry’s small bikes. However, I was so confident in my sizing system and the design that I offered to build another bike for free if she did not like it.

The bike was ready at the end of March 1975. I soon received a letter telling me how much Alice was enjoying her new bike and that she was always near the front of the pack on club rides, particularly on the climbs. Of course the fact that the bike came in at about 18.5 pounds didn’t hurt, but Alice will tell you that the improvement in fit had a lot to do with her improved performance as well. And of course there are hundreds of riders using Georgena Terry’s small front wheel bikes today who will tell you the same thing.
Bob Freeman

Pics
 

https://cimg8.ibsrv.net/gimg/bikefor...703f76692.jpeg
https://cimg2.ibsrv.net/gimg/bikefor...df82ab55e.jpeg
https://cimg9.ibsrv.net/gimg/bikefor...d45564f99.jpeg
https://cimg5.ibsrv.net/gimg/bikefor...37daded59.jpeg
https://cimg6.ibsrv.net/gimg/bikefor...9789a8bbe.jpeg
https://cimg7.ibsrv.net/gimg/bikefor...b391ea0ba.jpeg
https://cimg0.ibsrv.net/gimg/bikefor...79d9bc0ce.jpeg
https://cimg3.ibsrv.net/gimg/bikefor...888cc41ec.jpeg
https://cimg4.ibsrv.net/gimg/bikefor...b22987ff6.jpeg

Well, here it is. Maybe someone will see something that I failed to mention that eliminates any doubt. I'm still stoked I found it, whatever it is. 🙂

Other than size, color and your lack of decals your frameset appears to be identical to my 4000. bobsyourbike you're our real Sekai expert, what say you?

What a fun journey, and a super cool bike!

I rode across the US in the summer of 1980 on a Sekai - I'm pretty sure but not absolutely positive it was a 2000. I bought it new from Steve Howard at Livermore Cyclery early in 1980, so it may have been a 1979 model. (Steve was a high school buddy and one of the guys who got me into cycling.) I had a Bob Jackson that simply was not meant to do loaded touring, and the Sekai was the best I could afford at the time. It was a kind of champagne gold color (it looked pretty good) and had a collection of mid-range parts. The bike held up well for the 3,600 miles, except for the rear wheel. It simply was not meant to take the stresses put on it by my large self and everything needed for a self-supporting camping tour, almost all of which was in or on top of rear panniers. I go back and read my journal from that trip most years, and that rear wheel was the bane of my existence for two months. I had to replace a bunch of spokes along the way, and had to talk several shops into letting me use their vise so I could pull the freewheel (I had brought the right freewheel tool, along with a rather heavy collection of other tools - no multi-tools back then - so I could service almost anything on side of the road if I had to.) As frustrating as it sometimes was, I could not and do not fault the wheel - I was pushing it far beyond what it was meant to do.

Otherwise, that Sekai served me very well. With a beefier rear wheel, I would cheerfully have toured on it again except for one thing. I let my brother borrow it (he thought he might take up cycling for exercise) and it got left outside in the rain for at least one winter and maybe two. At that point, it was beyond redemption and I suspect it ended up in a landfill somewhere in the Central Valley. Oh well.