Today’s cautionary tale: Don’t ignore BB creaks

[Yellow Saddle]

Hi YS I was hoping for your opinion. The circumferential crack nearest the left crank goes further round, about 180° altogether. I put the current BB on in January and the axle looked ok then.

OK clearly wasn't OK. It had rust inside which you either didn't see or were seduced to not see because of the shiny outside.

Here's some incredibly good education on torsional stress.

https://www.youtube.com/results?search_query=tube+in+torsion

Somewhere on Utube there's a similar video on visualising torsional stress by using a split pool noodle. I just can't find it now.

The Google bunnies on here will do a better job than me. It does an excellent job at explaining how a tube fails in torsion.

 

[Yellow Saddle]

And to think the bike magazines hark on about how stiff these 2 piece designs are !

They are stiff. Much stiffer than other designs, including square taper. Stiffness doesn't equate to durability though.

 

[Drago]

I don't think the OP's one is very stiff any more, hence the joke about stiffness.

 

[I like Skol]

As has been commented on by YS, appears to be some serious corrosion on the inside of the failed tube and I expect that is the only reason for the failure?

 

[fossyant]

Square taper... nuff said (PS I do hove hollowtech/GXP on two bikes.

 

[Bianchi boy]

I’ve already ordered a 2nd hand 6700 chain set & a BB. Now at least the chain rings and cranks will match.

Keep the chainring bolts for spares, i `m about to order some £25......

 

[raleighnut]

Keep the chainring bolts for spares, i `m about to order some £25......

Not to mention the rings themselves.

 

[Svendo]

OK clearly wasn't OK. It had rust inside which you either didn't see or were seduced to not see because of the shiny outside.

Here's some incredibly good education on torsional stress.

https://www.youtube.com/results?search_query=tube+in+torsion

Somewhere on Utube there's a similar video on visualising torsional stress by using a split pool noodle. I just can't find it now.

The Google bunnies on here will do a better job than me. It does an excellent job at explaining how a tube fails in torsion.

Shiny seduction . Probably what happened, though I hope I didn’t deliberately or subconsciously ignore a crack. Even looking at it now I would have thought inside it’s just mostly wear and muck. It’s hard to admit to yourself a £350 chain set is knackered.
Is it still called ‘rust’ in aluminium? Don’t see why not I suppose.

 

[Svendo]

Not to mention the rings themselves.

I know, the rings on it are almost new. It’s a DA 7900 with an Ultegra 6700 outer and a DA inner. Interestingly the outer was half the price of the DA version but only 10 grams heavier, and some of that’ll be the wear on the old ring.

 

[cyberknight]

had the same with a H2 crank, snapped where the left crank bolts on

 

[Yellow Saddle]

Is it still called ‘rust’ in aluminium? Don’t see why not I suppose.

The spindle isn't aluminium, it is steel.

 

[Svendo]

The spindle isn't aluminium, it is steel.

Aha! That’ll be it then. Thanks

 

[Reynard]

Well, if you're going to break something, you may as well do it properly

A classic case of crack propagation through cyclical loading.

Steel is a material that has great durability, even when damaged, but then when it does eventually let go, you don't half know about it.

 

[dhd.evans]

I’ve had a bit of a BB creak for the last couple of weeks, out of the saddle. Assuming it was something else like it nearly always is I’d greased the drop outs and it’d nearly gone. I also thought it could be the new cassette settling into the freehub body gouges.
Turned out it was from the BB area as the crank axle gave out on the way to work, first press setting off from lights.
View attachment 485722

That... is impressive.

 

[Donger]

Happened to me too .... a couple of years back:

Mine had been creaking for a few rides too. All of a sudden, while out on a gentle, flat ride with a friend, it just suddenly failed. Got to a T junction while on the big ring, car on the left flashed to let me turn right in front of him, and I stepped on it to accelerate away. Crash, bang wallop! The next thing I knew I was stranded in the middle of a junction with both pedals pointing South.