Can you weld this?

[Entre425]

Hi Guys,

Just signed up here for some advice. Thought I would put it under the MIG section..

My bike frame has cracked near the bottom bracket, this is the part where the cranks fix to on the frame. Its quite thick aluminium compared to the rest of the frame.

From a welders point of view could this be welded and still be safe? Its only a few MM long and a hairline crack.

Thanks.
Here's a pic;

 

[500e]

There are a couple of members that build frames they will be around in time, possibly a couple more picks will help as well

 

[Wozzaaah]

Welcome to the forum.
It's almost impossible to see what's going on in that photo, can you post a better quality one please?

 

[Entre425]

Thanks guys. I will get some better ones for you ASAP.

 

[hotrodder]

Probably should wait for the better pics but we're looking through the right hand crank spider (granny ring is the blurry bit at top of pic) right?

Normally i'd expect the RH bottom bracket shell to have a lip where it meets the frame. Part of me is thinking this is what's actually cracked (but they aren't normally painted ) and there's a spacer between that and the frame to correct the chain line/deal with 68 versus 72mm BB shell.

If it is the frame that's cracked then it's a bit of a tricky one in that fixing it without destroying the threads in the BB shell will basically involve welding 'over' the crack rather than actually fixing it properly. It'll almost certainly grow back. Vee out the crack to eliminate it and the threads will almost certainly get damaged when welding. Can obviously chase and face the BB threads afterwoods BUT depending on the quality of the threads might end up with a BB that's prone to creaking in the future due to fretting from a slightly sloppy fit

ETA depending on wall thickness, depth of the crack etc might get away with using an old BB shell as a mandrel while welding to preserve the threads and roundness of the shell

 

[Wozzaaah]

It does beg the question...what frame is it?
If it's nothing special then I'd say bin it and buy another.

 

[robocog]

how about get a cup/band turned up to keep it from splaying open
locktite it on and forget about it

will also hide the chain rash

Being a bit of a pikey I would use a Mikalor stainless clamp on it
(or a Jubilee clip if skint at the time) and enjoy it for a while longer

I'm guessing someone did something odd putting the cartridge BB in for it to have done that?
(eg not gone in straight/galled/picked up thread and carried on regardless??)



Regards
Rob

 

[Entre425]

Its an expensive frame (Lapierre Spicy).

Thanks for the advice.
is it not possible to place a small plate over the crack and run a weld around that or will that not do?

Its hard to say the depth but it doesn't appear too deep. I have seen some bad ones in my time but it appears more surface than right the way through.

 

[hotrodder]

Right, so it's got a press fit bottom bracket instead of a traditional threaded frame? Google suggests that you aren't the first to have problems and frankly a press fit BB in an aluminium frame is a monumentally stupid idea IMO- been out of the bike trade for years and didn't realise they'd gone this route although i guess it's the next logical step after integrated headsets

Given the press fit i'd be amazed if that crack isn't an inside out deal i.e. is the result of either the frame not being machined for the correct interference fit, a monkey pressing the thing crooked or a combination of both. Similar result with headset cups and ally frames isn't uncommon

Has a warranty claim already been turned down? From a weld repair POV lack of threads doesn't make it easier since the press fit has to be 'just so', if anything worse as welding aluminium locally anneals (softens) it which is a bigger deal for a press fit than it is for threads. Jubilee clip has zero chance of working IMO and welding a plate over it won't do much either, the existing crack is a fantastic stress riser and it'll continue to grow underneath unless a hole is drilled at the end of the crack to arrest it which removes material from the press fit which'll already be compromised due to softening etc

 

[robocog]

whoa -
I have been out of the scene for a while
Cartridge BB's were "new tech" last I was involved ;-P
(I also had to Google integrated headsets!)

Everyday is a schoolday

Regards
Rob