So I recently found a Concord frame in a garbage dump and I decided, hey I want to build a fixed gear. I have almost everything covered except I attempted to put my new crank on it and I ran into a wall...

My square bottom bracket looks like this...


I notice that every bottom bracket I've seen has "internal threading" and I don't know what to do...

Do I have to buy a new bottom bracket (which would be fine... I just dont know if I need 68mm or what) or get a certain adapter

Please help out a noob

my raleigh is like this. I remember the outside diameter of the nut was 14mm, it was kinda shaped like a track nut.

go to ace and get a fitting nut and a lock washer?

How would I go buy using that nut with a standard Square Taper JIS?

It looks to me that you need this

?

on my raleigh the threaded bit sticks out past the hole in the crank so you can thread a nut on there.

or you could just buy the pin spanner and put in a new bottom bracket pending standard english threading.

I'm thinking of just buying a new bottom bracket? I'm just wondering if I need the 68mm...

Any suggestions to find out what size bracket I should get? This is the last part of my bike that I'm having trouble with then I can finally get out on the road!

Thats what I thought should happen but when I try to put the crank on it doesnt even get far enough to be able to put a nut on there?

Should I just apply more pressure to get the crank on?

hmm, if it's not even touching then don't try to force the crank on. chances are the threads won't have enough purchase space and will just strip.

maybe it's a taper incompatibility? tho jis is fat, so it should either fit fine or go too far. i'd just get a new BB, that one looks right rusty anyways. the lbs should be able to help you out in figuring out what you need if you're not sure on what size you need

Should I just bring my bike frame in or what?

Bike parts are usually in the trash for a reason. I would suspect that if the previous owner thought that he could get $10 for that bike he would have, especially in a big bike market like Chicago.

Chances are that you found the reason why it's in the trash. The rattle-can paint job may be hiding rust or cracks. It's definitely gummed up your BB lock ring.


That being said, you need both tools in this photo:

68mm is the width of the BB shell across the faces, you can grab a ruler and measure it. The other important spec. is the threading. If its English threaded, by far the most common, the drive side cup will be reverse threaded. You need to select a spindle length, which is determined by the crankset.

It was found with out the rattle-can spraypaint... there is no cracks or anything and its in good condition

I've decided I'm goiing to buy a new bottom bracket.. I plan to take the bike to the LBS tomorrow and maybe ask them a few questions to figure out what size bottom bracket I need

Rofl wow, come on people. That's just a regular square taper unit with threaded axle ends instead of the regular "internal threaded". Common on older bikes that take a 14mm nut at the top to secure the crank. This is neither unusual or noteworthy. The crank might not go on easily seeing the rust on the spindle. Take some wd-40 and some steel wool and remove it. Thats what happens when you post mech questions in the wrong forum.

+1

The Mechanics sub-forum is really good.

Well I ended up ordering a 68x113mm Shimano UN54 just to get riding...

If it doesn't work I'll attempt Operator's thoughts