Is movement in my bottom bracket an issue which requires attention immediately?

Question

TLDR; my bottom bracket has movement when it shouldn't but no other issues / sounds / clunking. If I'm riding a few miles a day, is this likely to break catastrophically, or will it last another year or two issuing the odd warning sign?

This is different to the question: Riding on a failing bottom bracket - what could possibly go wrong? as mine doesn't experience clicking.

I have an old (20 yrs) mountain bike. The bottom bracket has play in it, one side can move up and down 1-2 mm - I am guessing this is simple wear.

There are no other issues, no creaking, no stiffness, other than the movement.

I cannot replace the bb unfortunately, tried to remove the crank arm and it pulled the thread out instead of the arm! I also suspect I'd have issues getting the bb out too. Bike is worth next to nothing, but this is an advantage as it makes it less likely to be stolen.

Assuming this is simple wear, will I get warning signs before it dies, or will it just unexpectedly die on me?

I understand there is no definitive answer to this, given the lack of info/data on the issue, but would appreciate answers from those with experience of this.

Edit: this is a sealed unit, so one side screws into the frame and the other has a plastic screw(?) to hold it in place. No adjustment of cups is possible as far as I am aware.

To clarify, there are no sounds coming from the bottom bracket.

Answer 1

'Normally' the answer is 'Its worn out, you should replace it". This you already know.

Looking at this from several aspect is the key to making the decision.

The movement will cause the chain rings to slop around. A small amount won't affect things too badly, but eventually you will suffer poor shifting and chain slipping. The chain will start to slip as the chain rings move in relation to the derailleur. Worst case is a chain break, and very worst case would be the chain dropping off the cassette into the spokes and locking the rear wheel (although a properly adjusted rear derailleur should prevent this even with lots of slop in the chain rings). ,Eventually it will become unsafe.

I presume by "pulled the thread out" you mean the crank extractor stripped the crank arm thread. I had this happen once and found the cheap extractor was undersized. I was fortunate enough thread was intact that a workshop quality extractor had enough to pull the crank. If the thread really is stripped, you will need a new crank arm.

The bike as is has very limited life - I would not expect many more miles before it gets so sloppy its not rideable. Either retire it or look for used parts - a donor bike, a mate with a box of bits, or a local bike coop.

Answer 2

I'd suggest you try tightening the Non Drive Side cup and see if there are any improvements.

You don't even need to remove the crank for this. The right tool will just slip on, or you can get away with a big spanner and some plumber's sliding jaw grips.

If this helps the problem even a little, a proper clean and regrease will help a lot more.

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The risk in not doing this is that there will be damage done to the cones in your BB, and if metal flakes off the inside surfaces where the bearings run, then its toast and you will need a replacement. A cartridge bearing is relatively cheap these days, and is well worth doing even on a beater bike.

Answer 3

If there is play in your bottom bracket it means that the bearings are loose or worn out, it should be repaired soon because it will influence the whole drivetrain negatively, like sprockets and chain.