You have been very kind and I may had to relent to these PDFs. Thank you so much for sharing.

Annnnnd a question arises!

Background: The large chainring is swaged onto the cranks, which is seriously complicating my plan to switch to a single chainring. I'm exploring options, including having someone grind the teeth down on the large ring (leaving a chain/bash guard of sorts) or just replacing the whole dang thing. Current setup is Sugino GP (and I don't know more than that as I don't have the tools to get it apart yet).

On CL right now I see this:
https://portland.craigslist.org/mlt/bik/4029169290.html
and this:
https://portland.craigslist.org/mlt/bik/4026004109.html

The question, then, is about fit. If I decide to go with an entirely new crankset/BB, what size am I looking for when it comes to my Sekai? I'm hoping it's pretty standard and I'll have plenty of options for my little project.... but I dunno.

Thanks!!

....the tools to get it apart are pretty standard, a thin wall socket of whatever size
your crank bolts are (14 or 15mm) or the bicycle specific crank bolt wrench version,
and a standard cotterless square tapered crank puller.

I personally would replace the whole thing, but if you do that and go with a single,
you will need a shorter spindle to maintain a decent chainline.

Usually, the length of the BB spindle is specced for a crank by the maker, but
if you buy used and can't find it, you have to kinda eyeball it and experiment some.


Put up a picture of your current crank, if you can, because I'm curious about
what you have that would be swaged and unalterable from this time period.

Thanks for the info, 3alarmer. Now I've got more words to look up, too!



No spider = swaged, yes?

ahh I see you're in good hands here, but I do have on random tidbit to throw in. Those cranksets were popular with bmxer's, they'd turn the large chain ring into a spider for their bikes.. I only recall this from the hours I've spent researching components on sekai bikes of course.

Obscure trivia is always entertaining.

Dumb question Mr Oxley, does the large chainring aesthetically bother you? If not, just use it as is as the spider.

That was the plan I was originally considering... problem is the teeth grab my pants and such (casual biker). Grinding the teeth off seemed a good solution, but the quotes to do it are high enough to justify replacing the original assembly. Here's a pic from someone who did the teeth-grinding solution. It looks great and I have no problem with it if I can get it on the reasonably cheap:

It shouldn't be to hard to find a chainring guard that you can mount. It would a lot easier drilling 4-6 mounting holes in the large chainring than grinding off the teeth. Bevel the holes on the inside the ring and use flat head machine screws so the chain can't up on the screws during gear changes.

Pulled the 2700 down from the storage last week, and discovered it needed some work.... welp she's good to go now so I should be able to ride it before the wet weather hits!

Yeah, if you use that crank, you're stuck with the big ring.

I think if it were me, I'd probably experiment with just using the large, swaged on chainring as my single,
pull off the small ring, and find a big assed cog for my FG wheel that made the gearing something I could
handle on a FG. I'm not a fixed gear person (too old and one extremely ancient knee), but I think from
what I've seen locally here, it might be doable in terms of gearing.

If it's not a SS or FG project, then I don't understand why the large ring would not also be quite usable.

But it might come up a little less than perfect on your chainline. OTOH, it might work out, you never know.

Ah, yes. The "why?" question. hahaha

I've noticed in my riding, which is purely casual on the paved bike trails or here-and-there around town, that I have only switched over to the large chain ring once. And that was just to make sure it worked; I switched back after a very short time. In short, I only ever use the small chainring and so -- in the interest of modification for simplicity's sake, along with aesthetically making the bike more "mine" -- I decided to go five-speed instead of ten. Sure, it's an unnecessary mod if we want to get particular; I could just leave everything as it is and stay on the small chainring. But where's the fun in that?

In my youth I used to do the same thing to my guitars....

Oh, and I'm with you on "too old for that fixed gear" stuff. Sometimes I've gotta stop pedaling! haha

Is this conversation drifting away from the "Sekai Database" concept? Should someone move the last few posts to Mechanics, maybe?

.....you can get some very good advice in the mechanics forum on modifications of the sort you are proposing.

Unfortunately, it can take a while to figure out which is the "good" advice..........

Your best bet is to put up a new thread in there, solicit advice and suggestions,
show your photo or photos of what you have to work with, and describe as
accurately as you can your overall ambitions with this particular project.

If you are doing a lot of riding on your small ring in the front, and you are simultaneously
on some of the smaller cogs in back, you might experiment with some of the gear
ratios you get with the large chainring and some of your larger cogs in back to see
if you can find something comfortable. Gearing is important.

You can also Google up a bunch of info on bike gearing (charts and stuff) as a function
of front and rear sprocket tooth numbers.....quite a fascinating subject in and of itself.

.......like violins, they need to be played.

That is a good-lookin' bike, RS!

And yeah, 3alarm, experimenting with (and learning more about) gearing should probably be in the works as well. So much to learn. It's a good thing I'm enjoying it all!

Having trouble identifying the model of this Sekai. They're asking $150, but I don't think I would pay more than $100. Thoughts?

Based on the double butted hi-tensile tubeset, in conjunction with the Super Maxy crankset, alumuminum 27" rims and what appears to be aSunTour VGT rear derailleur and Dia-Compe 500 sidepulls, the most likely candidate is a late 1970s model 2500 (Gran Tour).

IMO, $150 would be a good price except in the softest of markets, provided condition is a stated. With college students returning to school, I would not think that that one would last long at that price.

Good to know! Living in the Seattle area, I've been intrigued by the story of Sekai and have been looking for one in decent condition recently.

Do you think anything would need to be replaced / updated? It seems like most of it is original and I don't want to change much but the tires seem worn and the shift cables / brake cables should be under the bar tape, IMO

............ in the ancient times, these non aero brake levers were run with the cables as you see them.

Luckily, we were too dumb to realize how backward that was, so mostly they worked fine.


On a bike of this age, you should probably pass on it unless you are mechanically sophisticated
wnough to be able to take most of it apart, regrease everything, and put it back together successfully.

Finishing up my earlier gearing discussion... Been reading up on gears: "useable" gears, duplicate gears, etc. Then yesterday I took my bike out solo to run a few errands around town. Found myself using the large chainring much more while out on the road without a small child strapped to the bike. In short, I think I was looking at reducing the bike to match my usual usage without thinking that maybe sometimes I'm gonna want all of the bike. So now I figure if I want a 5-speed hybrid commuter thing I'll buy one instead of turning this bike into one.

Project abandoned. New project: Impulse control.

p.s. That black one is pretty sharp, Cody.

@ RaleightSport, She is pretty. Did you like those shifters? I am very used to mine being on the frame.

@J Oxley, I think purchasing the 5 speed hybrid is better than destroying the original crank. Sekais are nice bikes. The Sugino Cranks are very nice and aren't easy to find anymore

@ Cody, Did you purchase the bike? Can you list the bottom bracket serial number? I like the look of the black frame.

Seems there are two at least two major versions of the 2700, or there was just a frame switchover at a certain year.
I have seen pics showing a Tange hi-ten steel frame sticker, and ones showing Tange Chamipion (with no number) I have a 2700 in my possession that has the Champion sticker, which I believe says cro-moly on it in tiny letters ( I would have to check when I get home).

The Hi Ten version 1 all seem to have flat seat stay tops. The only pics I can find that clearly have the same type of sticker as mine (version 2) indicating a Champion tubeset are all gold/tan in color, and have scooped seat stay tops. Mine is silver, and has bar end shifters, and braze on cable guides, but otherwise looks identical to the gold version 2 below. None of the pics below show GT deluxe on the top tube, mine does not either.

I am sorry to steal any pics, I will remove the links if the owner objects.

Version 1 :
https://www.ece.ubc.ca/~gillies/sekai..._about79_4.jpg
https://www.ece.ubc.ca/~gillies/sekai..._gt_deluxe.jpg

Version 2
https://www.ece.ubc.ca/~gillies/sekai...eftSeatlug.JPG

I will have to find S/N and date codes, but I am seriously wondering if there were two different tubesets at the same time for the 2700, or if there was a just a wholesale move away from the hi ten tubes in 1979-1980?

I have the very same bicycle as Version 2, it is posted early on in this thread. It is IMO a very nice bicycle. I wish I knew more about the Tange Champion tubing and I wish this bicycle were my size.

I also have Version 1........these came with some very nice components.....Suntour Cyclone black, Sugino Mighty Competition cranks, Suntour barcons all on a DB hi-ten frame. I parted my out because the frame showed signs of a front end collision and I don't think this frame is up to par with the Tange Champion version. Unfortunately the damaged one was my size.

Here's the Sekai 2400 I picked up this past weekend. I'd love to know more about it, especially how I should clean it up and what year it is.

Rear derailleur - Suntour V-GT Luxe
Front derailleur - Suntour 7
Shifters - Suntour
Brakes - Dia-Compe
Crank - Super Maxy
Front chainring - Suguino
Rims: Araya
S#: Y79 - 0507051

It's the first working bike I've owned in a few years, and I might be in love. It took me 20 miles on a first date the day I bought it, which might have something to do with it. I took it to a free bike service station on my campus and then to a community bike center where I was coached through a tune-up, which got it in shape and taught me a lot.

I've been prowling around BikeForums and this thread in particular while I did my research. I've spent way too much time googling this bike.

I believe it's a 1979, based on the serial number and components. Sekai seems to have used a pretty straightforward serial system, which I guess they altered between the late 70's and '81. I'm under the impression that most of the components are original, but a mechanic suggested that the brakes aren't.

Your mechanic buddy is wrong, your brakes are indeed stock. I am not fully caffeinated, but your bike is most likely a 79 .