Slight surface crack cause for concern?
 

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Just noticed this on my frame, wondering whether it's anything to worry about or just a surface crack in the paint, any opinions?

The first obvious thing to do is to pull the BB out and inspect the insides. There are dye penetrants that can capillary their way through a crack to the other side you could employee. I've used penetrating oil and really clean other side for this.

Could this only be a paint crack? Sure but I tend to doubt it. Have you even pulled the post out and shined a light down the seat tube? Andy

It's a very common place for lugged frames like that to crack. It won't be a catastrophic failure even if it breaks off completely, so I'd ride it till it breaks. There is no effective method of patching it, so tube replacement is the only real repair. You may as well ride it till it breaks and then make a decision on whether it is worth the expense of replacing the tube.

All cracks look small on the surface, until they look big. That's a very long crack, I would say.

Are there any symptoms while riding, e.g. derailleur rub? Although my sad experience with Teletyne titans says the crack has to get more than half way around before that starts happening.

I have seen some frames that look like that where there was very little filler in the joint. That's my suspicion on this one. Not sure how that happened. Seems like it would take a very inattentive person doing the brazing or a rank beginner. I assume it was hearth brazed. Might have been just before lunch.

My 1976 Fuji Pro broke right there after showing that crack for about 6 weeks. In a race. Not a big deal. Bike went instantly to feeling soft and floppy. Stopped, looked, then rode the bike back to the start/finish, looking down periodically to see the seattube waving back and forth.

Might not have been anyone there at all, if it was robotically brazed. That was a thing for a while there, before the revolution that switched all cheap frames to TIG-welded. Multiple torches pointed at the joint (I remember it as at least eight torches, probably more), sometimes with a motorized "waving" action so they aren't just pointed at one spot each. An infra-red "electric eye" tells it when it's hot enough, then spool guns feed brass wire into the joint at multiple points, brazing DT ST and CS sockets all at once. I've seen it in videos, but never in person. Since there are so many ways it could go wrong, I'm amazed that they worked at all, but from what I've heard millions of frames were brazed that way. I think they were used first in Japan, then later in Taiwan. Maybe China but I think by the time the tech had trickled down that far, the switch to welding was complete. My old boss Davidson saw it used in Japan but he didn't go to China.

Mark B

I was about to ask about automated brazing. I always thought the Japanese makers maintained a certain level of hand craft with their frames. I didn't know the Japanese used anything like that, but it makes sense to have a flat-topped bb shell if you do. Maybe that's a signal of machine brazing. Seems like there should be a puddle of brass on the outside if it fails, which would be fairly easy to pick up on inspection.

Thanks everyone for the input, if it won't be a catastrophic failure I will just keep riding it in that case, if it breaks I'll just replace it, only paid $150 AUD for the frame so not really worth repairing, I guess you get what you pay for eh

Can you open the crack by stepping on the pedal and push on the seat?

That’s this became more apparent after some brake rubbing and odd shifter noise

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about a 30 year old RockHopper. But my 2 year old Gunnar did the same.