Would you ride a bike with a 1cm nick in the BB shell?

[Bodhbh]

Been a bit of an idiot here.

While trying to remove a old chainset off a Kinesis Crosslight frame I'm building up, I had alot of trouble getting the crankarm off to remove the BB, stripped the threads on the crank remover - so I took an angle grinder to the crank. Yes, you see where this is going - as it cut thru the aluminum crank like cream cheese I managed to put 1cm long cut in the BB shell without noticing.

Basically, question as in title. Frame is aluminium, the cut right in the top of the shell, and 1cm deep at the surface and about 0.5cm by the time it reaches the threads. Think it would be wise to ignore it, or it's an accident waiting to happen?

 

[ttcycle]

Is the shell replaceable? Recommend that it gets replaced if possible. The BB is one of the areas that would take a lot of force as pedalling will impact on it so any weaknesses here are going to get worse and can be a disaster- last thing you want is for it to fall apart mid ride.

Sorry if it's not what you want to hear...hope others have more encouraging thoughts!

 

[hubgearfreak]

ride it but keep checking it.
if the crack gets bigger, then you've shagged it, if not, you've got away with it

 

[Steve Austin]

difficult to say if you should keep riding and if it will be safe. you might want to consider he effects of it breaking. is it likely to break and cause you to fall off?
If the cut could cause the frame to snap, then i wouldn't ride it anger again, but then again you could get a lifetime of riding out of it. but then again it could fail catastrophically at any minute..

have you got a photo?

 

[Steve Austin]

Is the shell replaceable? Recommend that it gets replaced if possible.

can you replace a BB on a aluminunium frame without the heat process wrecking the frame?
and how much would this cost? a new crosslight frame is only £199ish, so is it cost effective?

 

[Steve Austin]

i just found a new frame for £150......

 

[Jonathan M]

If it were a steel frame, there may be more chance of a repair or replacement BB shell.

I'm inclined to say don't ride it, the BB area is highly stressed at times, and as Steve says it may be perfectly OK, or fail catastrophically at anytime.

Besides, if it were me, I'd use it as the excuse to buy a new frame, and sell the old one on Ebay to recoup some of the outlay. Full description of the damage etc of course.

 

[P.H]

Not sure what you mean by "nick"?
If it's cut all the way through, sooner or later that's likely to spread, I'd ride it but keep an eye on it and look to replace it long term.
If it's a gouge that hasn't cut through, I wouldn't worry about it, I rode a bike with a deep gouge in the BB shell fom a chain coming off. there's plenty of strength past the 1 cm mark, just make sure the BB is a good fit, I'd loctite it in, but then I do anyway.

 

[Bodhbh]

Cheers all, the frame was 2nd hand and only 60 quid, so not the end of the world. I was looking to buy a Singular Peregrine frame (~450quid) but decided to be sensible with the cash - maybe like you say Johnathan it is an excuse to be not so sensible. I'll try and stick a photo up later.

 

[Bodhbh]

Not sure what you mean by "nick"?
If it's cut all the way through, sooner or later that's likely to spread, I'd ride it but keep an eye on it and look to replace it long term.

Yeah it's all the way thru. Although the nick is only about 0.5cm where it cuts right though.

 

[brodie]

It might be a good idea to smooth and round off the inside of the cut to prevent a stress riser. OK the frame's alu, but some steel frames have massive holes and cut outs in the the bottom of the BB shell and none of them break.

Just keep an eye on it for any cracks spreading from the cut. And if any cracks might eventually appear, the BB shell's not going to suddenly fall apart.

 

[Tollers]

If the nick as it a point of high stress then it sounds risky as it will concentrate stresses at the point of the cut. Also the direction that the nick goes in might be important. A photo will be helfull.

Has anyone (engineers) seen any FEA of stress load witin a BB?

Tollers

 

[Bodhbh]

Not great photos, as the camera has issues of it's own (smashed display):

 

[Matthames]

That frame has had it. You will end up getting a stress fracture that will probably propagate through the weld resulting in a catastrophic frame failure while you are riding it. So it is a new frame I am afraid.

Edit: You said you were having trouble removing the crank arm, a better solution would of been to use a blow torch to heat the crank arm and crank. The difference in expansion between the two metals would of enabled you to easily remove the crank arm. Probably something to note for future reference

 

[Bodhbh]

That frame has had it. You will end up getting a stress fracture that will probably propagate through the weld resulting in a catastrophic frame failure while you are riding it. So it is a new frame I am afraid.

Not really what I want to hear, but rather the truth. As it's already almost built up, might just give it a ride or 2 to get a feeling for the setup (it's my first drop bar bike). Those angle grinders are lethal near a bike