I needed to replace my old fixie frame with something lighter, and with a standard BB shell. So I came across this one online. The seller bought it off a friend who stripped and painted it, so any knowledge of its provenance won't come from there.

What drew me to it was the fork. Clearly quality steel rather than piece of pipe bent into shape like you see on cheaply built single-speed frames.

It has a serial number on the BB shell (Y5K2698), but googling for this only points weakly to it being Japanese, possibly built for the American market, possibly in 1985. But I suspect it's rather more recent than that.

There are no bosses for shifters, cable stops or eyelets for panniers or fenders, only one set of bidon cage bolts on the downtube, and the seatstays attach to the side of the seattube rather than under the seatpost clamp. The dropouts are semi-horizontal and about 20mm deep. No engravings on the dropouts as far as I can see [edit: dropouts are marked as Tange, so I guess the whole frame is tange steel]. Purpose-built for fixed or single speed I would guess, due to the lack of bosses or derailer hanger, but curious that it has forward facing horizontal dropouts rather than track ends.

Here's an image of the whole bike, and here's a gallery of details (sorry- I should have stripped it for proper photos of the frame only, but I just took some snaps on my way out the door to work!).

Whole bike

If anyone can help I'd be grateful for your knowledge. Won't change anything of course; the bike is still a pleasure to ride irrespective of its provenance.

  • 2
    See this thread: bikeforums.net/road-cycling/327417-identify-road-frame.html
    – Batman
    Commented Apr 24, 2014 at 2:23
  • 2
    Goodness! Could it be the very same frame? I mean, if it has an identical serial no. then it must be, right? And Yamaguchi?! I had suspicions that it might have been, but I dismissed that as too fanciful.
    – Jangari
    Commented Apr 24, 2014 at 2:26
  • 1
    I emailed Koichi Yamaguchi and he said that it's not his, and that normally, he can identify frames by looking at them, but this one he says he's never seen before. The serial number also does not match. Yamaguchi's serial numbers are of the pattern KBOxxxx. So the person on that forum must be wrong. I should look inside the headtube for any info. I did see that the rear dropouts are stamped with 'Tange' and something else I can't read. So that's a start!
    – Jangari
    Commented Apr 25, 2014 at 6:33
  • Specifically I have no idea, but I'd go with late 80s or early 90s road bike. Bottle bosses weren't super common in the early 80s, but it still has an old school quill stem. The front forks look odd and chromed - are they steel too? The bars have obviously been swapped or just cut. BTW that red rear light should be on the seat post not the seat tube - it is obscured at some angles by the seat stays. Personally I think black bikes are a magnet for thieves, any other colour would be better.
    – Criggie
    Commented Nov 28, 2015 at 8:27
  • 1
    @Criggie nothing more than in this thread. That said David's answer is a lead that I hadn't thought of before. In any case, the bike's now for sale!
    – Jangari
    Commented Mar 3, 2017 at 22:43

2 Answers 2


I think it's a 1980 Sekai 2400 model, all the hardware is upgraded and it's been painted for sure due to no decals. I have one similar and still trying to date it. but serial is very much the same

  • Thanks! All moot though since I sold this bike a few years ago when my knees couldn't hack it anymore.
    – Jangari
    Commented Jan 29, 2021 at 21:37
  • Could you include the serial number for comparison purposes?
    – DavidW
    Commented Jan 29, 2021 at 22:24
  • @DavidW here you can find 3 Y0G8259 Y0G7816 Y1N0180 and if more are needed have a look in bikeforum.net (before the hosted picture disappears, you never know...)
    – EarlGrey
    Commented Feb 2, 2021 at 17:00

The serial number is the format for Yamaguchi Sports of Sakai Japan. Completely seperate from Koichi Yamaguchi.

Yamaguchi of Sakai was contracted to build frame for many different brand names around the world, including Sekai in Washington state.

  • Welcome to Bicycles @David. I see you've answered a few questions, but have not yet taken the tour; we recommend that new members take the tour to make best use of the site.
    – andy256
    Commented Jan 2, 2017 at 20:58

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