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My 2007 Ghost AMR 5700 developed a crack or fissure at the upper end of the headtube. I do not know whether it developed over time or whether there was a specific event leading up to it; it looked like that when I discovered it first.

Still, everything else on it is in good condition. The bike obviously is not worth its weight in gold, but it would be a bummer just to throw it away.

Questions:

  • How on earth can a crack develop at that point (it's about 10:30 o'clock when viewed from the sattle)? I am riding slow and methodically on single trails, I don't race downhill, and am pretty sure that I never once "punched through" the front suspension (sorry, don't know how you would call that in english); I do tend to not put my full body weight on the handlebar anyways for the sake of my wrists. The location just seems a bit arbitrary. Or is that a common place for these kinds of injuries, for some reason?

  • The bike is the entry level of the AMR line from Ghost, it cost about 1700€ (?) in 2007, and the parts are certainly not high-end, but appropriate to my needs; I like the bike as much today as in the past, and have not tried other fullies since then, so have no comparison anyways. That said, would you say it makes sense economically to look for a new frame (Ghost or different brand) and move everything over? I do have a family member who built his own road bike for a world tour from scratch, so the necessary know-how and maybe even most of the tools should be around, although he has no experience with suspension.

    But I have no idea how to select a proper frame, and frankly don't want to make this my "project" for the next year. I guess I'm asking how hard it is to find a fitting frame, or how easy it is to botch the choice. It would only make sense if the result would be able to run single trails again (not crazy downhill with lots of jumping, I'm not getting younger).

  • I don't even dare to ask, but will do so just for completeness: would a competent welder be able to fix that crack, and would you trust your own life to it afterwards?

The crack itself: the crack

The specs from their 2007ish paper catalog: specs

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    Put a hose clamp on it. Ugly, but it will slow down further cracking and greatly reduce the chance of a sudden failure. – Daniel R Hicks Apr 29 '18 at 12:52
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    @DanielRHicks Your advice is extremely unsafe!! The frame is toast. – justathought Apr 29 '18 at 17:55
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    It does look like a crack to me. You should try to get a new frame, but DRH does have a point -- sometimes you can't, and you have to live with a cracked frame in which case, a hose clamp is one of the better solutions. – Batman Apr 29 '18 at 19:03
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    @Criggie, I wouldn't trust it even if I didn't see any light - the crack might be meandering in an erratic way through the material, seemingly blocking the light. But thanks for mentioning that there are brands with a lifetime warranty. That will certainly be a consideration on my next purchase. – AnoE Apr 29 '18 at 19:38
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    @Criggie - Hence my suggestion of a hose clamp. A little ugly, but as effective and secure as your heated metal band, with a lot fewer complications. – Daniel R Hicks May 1 '18 at 1:17
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Q: "[W]ould a competent welder be able to fix that crack[?]"

No, that frame is done for. By attempting to weld such a crack, a welder would prove their incompetence.

Even if you fix that crack you might find another crack on the right hand side, mirroring this crack. What is more, the crack will go considerably deeper.

I had a crack at the same spot and we asked the manufacturer (Corratec). According to their frame builder welding would warp the head tube too much to seat the head set properly.

Q: "[Why] can a crack develop at that point[?]"

Aluminium is susceptible to fatigue under light dynamic loads.

The upper bearing of the headset is pressed into the headtube at this point.

The position of the crack suggests it is caused by a force pushing the upper bearing forward. Due to the great mechanical advantage of the fork/headset system forces pushing the wheel backward require the upper support to bear a force pointing forward. This strains the upper support. (The lower support is compressed).

When you pull a ring from the inside it will typically break at the same points your tube cracked. (If I remember correctly from undergrad engineering ±2/3π from the direction of the force.) (Try it for example with a bagel.)

If your headtube showed cracks at any other place it would suggest machining tolerances not met. A head tube that is too tight cracks when the upper bearing race is pressed in. These cracks would then grow, for example, due to stress corrosion cracking.

Q: New frame?

Have you tried to ask Ghost? Corratec have given me a new frame when their ten year old frame failed in the same mode.

PS: Do not ride your cracked bike! Not even a single metre: it might fail catastrophically without warning.

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    I have sent a mail to Ghost when asking this question; I'll see what they respond. – AnoE Apr 29 '18 at 15:48
  • I like the idea of doing engineering experiments with bagels. – Holloway Jul 9 at 8:39
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Re finding a replacement frame.

New bare frame sets tend to be high end models. You could look on the used market for an older good quality frame, but you would have to educate yourself about geometry and component compatibility. It’s not impossible but not trivial.

Then factor in the tools you would need to buy to do a full bike build, and components that might need replacing such as the chain, cassette etc.

You will almost certainly be better off buying new bike, and getting the benefit of brand new components.

If you want some value out of the bike, strip its components and sell them - or donate the bike to a local co-operative or bike charity as a component donor.

  • New bare frame sets tend to be high end models. I thought so, thanks for confirming my suspicion. I don't see myself peddling all those old components, thanks #2 for pointing out that there are things like bike charities. – AnoE Apr 29 '18 at 19:05
  • The bike is 10+ years old; not worth it. I'd donate the parts. If you really want to reuse them, an off brand frame (e.g. from Nashbar) is probably whats best (I'd trust Nashbar or similar much more than some random Chinese site). – Batman Apr 29 '18 at 19:40
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No, on any reasonable frame cracks cannot be welded unless they were at a location that was designed to be welded. A reasonable frame means lightweight here, meaning that material thickness and thus strength at all locations is optimized to be just barely enough. Welding seams have lower strength than the original material, and therefore, any welding at that location will eventually fail.

You wondered how a crack can form at that location. The reason is simple: the material thickness/strength is optimized so that every location of the frame has just the bare minimum amount. Thus, there are many potential crank locations, including the head tube.

  • Kind of frightening to think that even well-known frame builders (Ghost has a good name at least in Germany, not sure about the rest of the world) simply break like this. I did not ride that bike as much as I would have liked to ("real life" kicked in hard not long after I bought it...), and it still failed just so randomly. I mean, I can accept if there's an accident and something warps beyond repair, but "not like this". ;) – AnoE Apr 29 '18 at 19:09
  • Luck of the draw. There are millions of Toyota Corollas out there; sometimes you buy a lemon or one that goes wrong. On top of that, rough riding brings out faults (and even bits of mountain biking is rough). Generally the only frames that can be repaired are steel, and its generally the tougher ones like touring bikes. Though repairs are becoming more and more limited as time goes on due to the points juhist made. – Batman Apr 29 '18 at 19:42

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