jpizzaj

Ok so my old Nishiki has cottered cranks and for quite some time now i have done my best to maintain them and have in the process become quite the cotter master, however long story short I'm throwing in the towel, i like the look but i cant stand on it without the left crank slipping several degrees.

anyhoo, i want to convert to a square axle and i have found an old set of cranks online i want to put on it but i figured i'd go all the way on the bottom bracket and get a sealed one, unfortunatly there are just waaaaay too many options out there and i have no idea what the correct one to get would be, i was overwhelmed by the info on sheldonbrown and am now even more confused than before.

I want to buy a sturdy bottom bracket but i am a broke college student so i need a low cost range bracket so please don't give me the "the best out there is" speech. what do i have to measure to ensure i am getting the right one?
on that note correct me if im wrong but since the cotter axle goes all the way through the arm and square axles stop within the crank, i will have to get a shorter axle then what i currently have? and if so how much?

i am a very knowledgeable guy with tools and measurements so dont be afraid to get technical, however i know nothing of brand quality of bike parts and such.

Grand Bois

It's very simple. You buy the bottom bracket size that is recommended by the manufacturer of the crank you'll be using.

bikeman715

A shimano sealed BB will work for you . You need to find out what lengths axle will work with the cranks you are thinking of buying. The length can range from something like 110 MM and up to 127.5 MM . I would try a 113 MM up to 118 MM and see how the chainline is and the clearance between the chainrings and the chainstay , 5 MM clearance is what i go by. measure the BB shell of the frame, it should be 68 MM. The price of the BB should be $ 25 - 30 .

wrk101

+1. And if you want a cartridge bb, the cheapest ones are Shimano UN26. They are on the heavy side, but nothing wrong with them. Of course, the cheapest option is to find some used parts or a donor bike, complete with a bb and crankset. You can find UN26 bbs on line for $10 to $12. In your case, I would not buy one on line, as the shipping will get you, and you do not have the size locked in. I picked up a UN26 at my local bike shop for $20 yesterday.

desertdork

Old as in used, or old as in new old stock?

If used, there may be the risk of a worn/damaged taper.

Thought it to be worth mentioning.

jpizzaj

they are old and used, i think they are from the 80's model of my bike, they're on ebay right now and if i win on them tats the plan, i guess im going to have to wait until i f i win them to figure this out then, hmm...