abshipp 

I've had this 1985 Schwinn Tempo for most of a year now.

When I got it, it had some pretty rough paint, so I had it stripped and powdercoated.

Before I installed all the components, I sprayed Corrosion-X inside of all frame tubes to help mitigate any current corrosion and prevent any from forming in the future. The great thing about this stuff is that it wicks everywhere and sticks tenaciously to the walls of the tubes.

I recently noticed some of this stuff weeping out of the downtube-BB shell joint, and decided to investigate further. I cleaned everything up, filed away the powdercoat around the suspected area, and noticed a crack right on the braze joint, maybe 1/6 the way around the downtube. I then took the bike out for a little spin around the block, really mashing hard and trying to make the frame flex a lot. I put it back on the stand, and this is what I found:




The black stuff you see is the Corrosion-X weeping out of the crack.

In your opinion, would this be more likely caused by a crack in the brazing, or a crack in the tubing itself?

I'm trying to weigh my repair options here. There is a framebuilder reasonably local to me that I would be willing to take this to if it's just a matter of re-flowing some brazing into the joint, but frankly this frame isn't worth having a tube replaced.

Thanks so much.

JohnDThompson 

Looks like a void area, where the brass didn't fully fill the space between the tube and the BB shell. Hard to say if it's more than a cosmetic issue. Can you see brass penetrated to the end of the tube inside the BB shell? If so, likely just cosmetic, but keep an eye on it. If/when you repaint the frame you can have the void filled with new brass.

abshipp 

I'll pull the BB tomorrow and take a look to see if I can see any brass inside the shell. As far as it just being a cosmetic issue, do you mean that I will just always have the framesaver weeping out of the crack, maybe screwing up any paint application at that area?

Thanks for the reply!

JohnDThompson 

If the Framesaver was applied to the inside but has migrated through the void to the outside, that's a more serious issue. It means there is an extensive void that could compromise the joint. Failure of a joint at the bottom bracket is unlikely to be catastrophic, but it would be a major joint failure.

unterhausen

a void that looks like that on the shoreline is probably bad news, nothing inside. Must have been quitting time.

TiHabanero

Looks to me that the joint is already in failure. the ends of the "void" show cracks formed along the edge of the lug.

Some info to add for thought. The first frame I built had only half the socket on both chain stay/bb joints filled. Could not fill in as the filler just rolled off the tube because the gap was dirty and I was unable to sufficiently clean it out. I road it as my main bike and commuter bike year round in the snow and salt, rain, etc. for 10 years like that and it held together fine. After hitting it with a car I pulled the rear end off the main tubes and found the sockets had some surface rust where the filler was not present, but the tubes were fully intact and actually reused to fix a busted chain stay on a production bike, which as far as I know, is still being ridden. This took place 7 years ago.

abshipp 

Yep, framesaver is migrating from the inside of the bike to the outside. I stripped the frame today, and could not see any brass at all around the joint. The only thing I can see on any of the joints inside the BB shell is where they were initially tacked.

The downtube does not show any signs of cracking, so that seems to confirm that there is a void in the brazing.

I will say that the photo is a bit misleading, the black in the picture is not empty space, but framesaver that has wicked out of the crack onto the face of the BB shell downtube socket. You can see the beginning of the crack down and to the left of the black in the picture. The entire crack looks like that.

Very interesting. I go back and forth between thinking that even if there is a significant void in the brazing that the bike is still likely quite structurally sound and safe to ride, and that since there is a void in the brazing the stresses on the BB shell area will eventually cause tube failure due to the presence of stress risers from the gaps in the brazing.

Who knows, maybe a little bit of A, and a little bit of B. I'm certainly not putting out gobs of power, but I'm a decent sized guy and sometimes like to get out of the saddle to mash up a hill in the big ring.

I'm thinking that for now, it will hang on my wall and might make a trip to a framebuilder for an in-person evaluation. Maybe I'll get lucky, maybe I'll get a stool?

​​​​​​​Thanks for the help, everyone.

wsteve464

Take the bottom bracket out and put your finger inside and see if you can feel a crack.