wems

I recently bought a vintage bicycle off craigslist for 40$. I am not sure of the year but it is 70-80s, it is a ZebraKenko which I have read is an old Japanese bike maker. My bike looks exactly like this one, but with more scratches:
https://www.flickr.com/photos/rottman/4558421347/


I am trying to fix it up and I just got the bottom bracket off. I have measured it and seen Sheldon Browns site about bottom brackets but I am still a little confused.
from here:
https://sheldonbrown.com/bbsize.html
A= 31-32mm
B= 54mm
C= 34mm
D= 122mm

I am thinking of buying this new bottom bracket:
https://www.amazon.com/Shimano-Square...bottom+bracket

I was thinking of getting the 68x122.5 but I am not sure if that part is even compatible with my bike or if that size is even close to correct.
One, thing with the old bottom bracket on the bike is that there are threads that go through the bottom bracket and stick out about 10mm on each side. I can't recall what was specifically attached to them. I can upload a picture of this if needed. Basically take sheldon browns picture of a bottom bracket and add threads to each end that stick out 10mm.


My second question is about the rear derailleur. I bought a new one from Amazon, and when I received it everything about it was much bigger than the one that came on the bike.. So, did I buy the wrong kind of derailleur for my 12 speed vintage road bike?
https://www.amazon.com/gp/product/B00...ls_o04_s01_i01
that is the one I bought. Will this still fit properly or do I need another one?


Thanks in advance for the help! This site has been amazing in my bike ownership experience.

FMB42

It seems that some of the Zebrakenko BBs of that era were 70mm x English (24 tpi) threads (I can't be sure about this tho).

Quote "...there are threads that go through the bottom bracket and stick out about 10mm on each side"

Some BBs use a slim "ring nut" (rather than a threaded "cup") that, when installed, leave about 5-10 milimeters of threaded bracket body showing on each side. Here's a link that shows a similar BB (see 4th photo).

https://hilarystone.com/bottombracketeng.html



Here's a link to a similar (unfinished?) "build" that may, or may not, be of help:

https://www.pedalroom.com/bike/zebrakenko-thunder-739

Your BB length will, of course, depend on what chain line you're running. Just be sure to double check the SB chainline measurement guide and instructions before you order.

The R.D. you bought is compatible with 6 and 7 gear clusters and, as such, should work regardless of its physical size. Just make sure you run a compatible chain (speed wise).

Good luck and let us know how you do...

FBinNY 

You need to match the spindle length as close as possible, but there's wiggle room of a few mm. The spindle length is to the ends of the square taper excluding the threaded stud. Feel free to save some weight by upgrading to a comparable hollow spindle, except you'll also need to buy the spindle bolts.

Yes the derailleur will fit. But your bike has a derailleur hanger built on, so you'll remove the hanger and mount directly to the frame using the large bolt in the upper body.

Hint- there's an angle setting (B) screw in back. Be sure to pull the RD back so it clears the dropout as you tighten. Trapping the B-screw is a common newbie mistake.

dsbrantjr

If the spindle and cups are in good condition you could just replace the balls, re-lubricate, adjust and ride and save youself the hassle of BB replacement..

wems

This is the picture of the BB without the ball bearings and what contains the BBs, its outside and im too lazy to go grab them. This is what I mean by 10mm of thread sticking out.



I have not looked at it too much but the BBs do not look like I can remove them from the end pieces. I guess they are semi-sealed? If I did just clean them up and relubricate them would it ride like it was brand new? The new bottom bracket would only cost about 20$ shipped

Bill Kapaun

That spindle simply takes nuts instead of bolts.

There should be a "code" stamped on it like 3-P, 3-S or similar. Possibly 5-?

POST that and the rest is easy, or look it up on Sheldons chart and pick the symmetrical equivalent from the far right column.

3alarmer 

I don't have a really good feeling about the direction this thread is headed.

If you ever overcome your laziness, snap a better picture of the bearing race
surfaces on your spindle, which may be a little pitted in your photo, but I
cannot tell for certain. The end pieces (called cups) also have bearing
surfaces that need to be cleaned and inspected for pitting/wear.

The bearings themselves may be good or bad... are they still shiny ?

I'd tell you about those threaded ends, but I'm exhausted by what I've typed
so far, and need to take a nap now.

wems

the code is
5S
81-G

Phil_gretz

Looking at the BB spindle in your photo, this one is NOT symmetrical. The drive side is clearly longer than the non-drive side. Just get 22 new ball bearings from your local bike shop, clean the cup and race surfaces thoroughly, grease, and re-install with 11 loose bearings on each side. Adjust and you'll be fine. Don't waste money on a new bottom bracket for this bike...

dsbrantjr

"would it ride like it was brand new?" Possibly not. Will you be able to tell the difference? Probably not.

Bill Kapaun

The chat shows a 3-N and 5-N. You can see the difference on the chart.

Add the same difference from the 3-S to 5-S to get the symmetrical equivalent.

OR, if the races are good, just buy some new BB's and regrease. Cost about $2.