hi everyone,
so on a long slow ride today, i noticed that my cranks are wobbling slightly back and forth as i pedal. i stopped and checked it out, and on the non-drive side of my bottom bracket, the thing (sorry, don't know what it's called) that is ridged like the side of a dime had screwed loose a bit. i tightened it up as best i could, but the cranks still wobble - i know i need a tool for this.
what tool should i use?
does this mean i need to overhaul the bottom bracket?
what could the reason be for this problem?
thank you so much for any advice.

depends on your bottom bracket as to what kind of tool to use. if you have an old one (cup and cone) you need a hook spanner, which is also used for removing fixed gear lockrings, so maybe you have one. if you have a new cartridge bb i hear that you just toss it and get a new one. you would need a special tool to remove your particular bb. kind of like a freewheel remover.

if it doesn't smooth out after you tighten down the lockring, it (probably) means your spindle is worn or your bearings are. In any case, when you get the tool you may as well take the thing apart and service it. Look on the Harris site for good doityourself instructions. look sharp for wear on the spindle or balls. you probably need new ball bearings at the least. but this, again, is all cup-and-cone advice.

check this out https://sheldonbrown.com/tooltips/bbcups.html
edit: this too https://sheldonbrown.com/tooltips/bbadj.html

i don't know your experience level at this sort of thing, but if you want to do your own repairs i can recommend getting a copy of Lennard Zinn's Zinn and the Art of Road Bike Maintenance. it's great.

It sounds like your BB and/or cranks are loose. Take it to broadway tuesday, and have them show you whats up and the fix. They're open 8-6.

That's your lockring that came loose. The "ridged like a dime" part means that it's an old loose ball or caged ball setup, not a modern cartridge style.

https://www.parktool.com/repair_help/FAQadjbb.shtml

That'll show you how to set it up right and what tools you'll need.

I will second the Park Tool online reference. I refer to it time and time again. So useful.

wow. that is a really good reference. puts the harris link to shame.

i ended up going to broadway bikes on friday to fix my bottom bracket - it needed a complete overhaul, and i've only worked on one-piece cranks on old three speeds before. anyhow, i'm SO glad i did because it turns out my bottom bracket is swiss threaded (?!) which i'm researching now. i definitely needed more tools than my friends have, and the expertise of the staff to not **** things up. the cranks are tight, and i learned some new stuff. also got my chanline in better shape. an excellent way to blow off work, and thank you for encouraging me to go to them and not just half-ass it with borrowed tools.