Lock ring won't reattach on bottom bracket I purchased a road bike and the lock ring wasn't attached, it just hangs loosely on this spindle:



It doesn't seem to reattach by screwing it in like one would expect. I tried screwing it in either direction and it simply doesn't catch. How do I reattach this ring, and what are the consequences of leaving it unattached?
Not attaching it will be bad, the thing it's there to lock will loosen or tighten as you pedal. What it does depends on whether it's a left hand or right hand thread.

Looking at it, it might be a right hand thread, meaning a French or Italian bottom bracket. So it will tighten up as you pedal. That's unusual and may be the reason the lockring is loose (whoever took it off turned it the usual way, it didn't go on, they gave up). If so, you're lucky and it's just a matter of putting it back on by tightening it the usual (right hand/clockwise) way. It may even be that the BB has a right hand thread and the lock ring is a replacement with left hand thread, and that's never going to work.

But it might not be, the photo is not really clear. The thread is quite fine so it can be hard to get it started. If the thread is damaged you're going to have to fix or replace it, so it's worth spending a bit of time trying to get it to screw on.

You may well find that the reason it's loose is that it won't screw back on, and possibly that the reason the bike was sold is that that renders it unrideable. Or, if it is a right hand thread, that they're so annoying to work on and relatively rare as a result, that the owner decided to give it up as a bad idea.

Fortunately the parts required are relatively cheap and readily available. Unfortunately you need special tools to do that change.

You will need:


a 6mm or 8mm allen key to undo the crank bolt (visible in the photo)
a crank puller (maybe)
a bottom bracket spanner (BB spanner)


(edit - thanks Carel) It looks very much as though there are "self extracting" crank bolts - if you undo the bolt in the crank it will hit the ring that's been screwed in (you remove that by gripping onto the two little holes in it), and push the crank off. If it's been there a while it will help to lubricate the bolt/ring interface, ideally with grease but oil will also work. Removing that crank will give you much better access to the lock ring.

You can do this two ways: find a replacement lockring and BB cup and just swap those. The parts should be nearly free... if you can find them. It's not worth paying someone to do this, so you'll need to rely on the friend who has the parts also having the tools.

The other way is to buy a modern cartridge/sealed bottom bracket and fit that. You really need to know which threads are on both sides of the BB to know what BB to buy, so first you need to pull the cranks and extract the existing BB. Personally, I would buy a sealed BB to replace that open one, so I wouldn't be too fussy about how exactly I removed the bottom bracket. But keep the axle, you need to measure that to determine who long it is because that's the key measurement when buying a replacement. Be much more careful about pulling the cranks, you need to keep those.

This is what a bike shop will do. You're probably looking at $40 or more for the bottom bracket and $20-$30 minutes of labour. Or buy the BB and borrow or buy the tools ($30-$40 off Amazon or eBay, more from your local bike shop).

Assuming it's not a standard/British bottom bracket, your choices are a non-threaded "universal" BB that just sits in the frame held by screwing the two parts together, and a threaded one that actually screws into the frame. The former will probably be easier to find, but be aware that it will almost certainly damage the threads in your bike over time, so once you put one in you can't go back.