BB woes

[colinr]

My fixed has developed play in the cranks, signs point to a failed bottom bracket (with cranks vertically there is play if I push/pull them into/away from the frame - the whole crankset moves so it's not a lose crank).

Removed cranks, removed BB, no sign of damage or wear. It's only 3 months old with dry weather riding only.

Put BB back in, cranks back on, rock solid.

One ride later, the play is back.

Any ideas?

 

[RecordAceFromNew]

Which BB and which crank?

 

[colinr]

Stronglight JP 400 Bottom Bracket with Stronglight Track 2000 Crankset.

 

[Zoiders]

I would check the BB shell and the seat stays to make sure there is not a fracture.

 

[Alien8]

How tight do you screw the BB down?

Does it seem to be unscrewing?

Maybe a bit a of thread-lock.

 

[colinr]

Frame and BB are only three months old so hope it's not cracks. Have looked and no sign of such things.

BB was tightened until it offered resistance, then a tad more. It may well be unscrewing, shall have to test.

 

[Zoiders]

I think you have cracked a weld, you might have missed a hairline fracture that is opening up under pressure.

 

[colinr]

On the BB or the frame? I've a spare BB, shall be trying that tonight.

 

[Zoiders]

Possibly where the chain stay meets the BB, the shell itself will stay in one piece but you will get flex/play if you have got a crack as it's not anchored to the frame properly anymore.

 

[colinr]

When it was freshly fitted and tightened there was no play though, I'd expect a crack would make it impossible to get that.
Wouldn't it? Really hoping the frame hasn't died on me.

Does steel even fracture?

 

[Zoiders]

If it's welded then yes it can break, BB's can flex in relation to the frame when you ride them, a crack near the BB would exaggerate this.

 

[colinr]

Took it apart again, no sign of any frame damage so with a better quality BB tool and some help we got it in good and tight.

It's held out against as much punishment as I could give in over a few miles, so hopefully was just a case of the original BB tool not getting it tight enough.

Thanks as ever for suggestions and advice.