Originally Posted by
loky1179
I can only speculate on the cause. If it had only been the head tube crack, I could have chalked it up to a number of reasons - corrosion, improperly seated cup, random stress. But when I found the second crack, I've got to believe there is an issue with this particular set of tubing itself. The bottom bracket cup is aluminum as well; there's no exceptional corrosion there, and as much as I'd like to think differently, I'm just not strong enough to create exceptional stress!
I'm pretty sure the guy I bought it from didn't use it in the winter; it was way too clean. So it only has one winter commuting to contribute to the corrosion issue.
You misunderstood me. I'm not talking about external surface corrosion. The issue (I suspect) is
INTERNAL corrosion between the frame and head and BB cups. Aluminum "swells" as it corrodes, greatly increasing then internal pressure stretching the thin "rings" of the head tube and BB shell.
I'll net a few beers that if you knock out the head cup you'll find plenty of whitish powdery material there, likewise at the BB shell - if you can get the BB out.
If riding bikes in wet weather, especially in salty wet weather, it's absolutely critical that all cups, BB, and seatposts are greased well enough not only to prevent galvanic corrosion, but to fill any crevices that water might otherwise wick into.
As I said from the beginning, I don't believe this was a failure of the material. Instead it was a failure of the maintenance protocol.