Framebuilders - possible dangerous crack at lugged seat tube/BB join? (pictures)

Today I was doing some touch-up (with clear nail polish) on my 1987 Centurion Ironman Expert (http://www.unc.edu/~cupery/pics/bikes/Centurion_Ironman_Expert/IMG_1520--Centurion_pink_bike_900.jpg) frame (Tange #1 butted cromoly tubing), and noticed a crack in the paint along the lugged joint between the seat tube and bottom bracket. The crack is on the back of the seat tube, toward the left (non-drive-side). It's a slight crack in the paint, and I don't know if it heralds any danger of a crack in the brass brazing material that's directly underneath the paint at that point.
I bought the bike off of eBay, but it's been in good shape and so far as I know has never been crashed. I did slightly spread the frame's rear triangle (using the cold setting method recommended by Sheldon Brown) but only went from 126mm to 128mm spacing. I think of this only because Sheldon's method requires the lever arm to be braced against the seat tube in order to apply force. But it's not like I stomped on the frame or anything; I was quite careful.

I'm guessing this isn't something to be very worried about (though I'll be sure to watch it) but would like to hear feedback. I know it's possible to sand away the paint just at that point and look at the brazed joint, which I may do but would rather not if it's unnecessary.

Anyway, here are three successive pictures zooming in on the same shot, followed by a zoomed-in shot from a slightly different angle.

http://www.unc.edu/~cupery/pics/bikes/Centurion_Ironman_Expert/IMG_7215--seat_tube-BB_crack_800.jpg
http://www.unc.edu/~cupery/pics/bikes/Centurion_Ironman_Expert/IMG_7215--seat_tube-BB_crack_closer.jpg
http://www.unc.edu/~cupery/pics/bikes/Centurion_Ironman_Expert/IMG_7215--seat_tube-BB_crack_closest.jpg
http://www.unc.edu/~cupery/pics/bikes/Centurion_Ironman_Expert/IMG_7211--seat_tube-BB_crack_closest.jpg

There's a lot of paint built up on the lug edge so it's a little hard to tell if the crack goes goes down into the metal. You might want to load the frame with a pedal and see if the crack opens up at all. If the seat tube is cracked it will need to be replaced - not an easy repair.

Try to remove the paint around the crack and if indeed a crack then bring it to a good welder. Better safe.

You've got a brazed frame, not welded.
There's a good reason for brazed frames to have lugs. The lug will hold the tube to the bottom bracket, even if the brazed joint fails.
I would keep an eye on it to see if the crack widens, but for all we know, it might be only as deep as the paint.

Yesterday my 1984 Centurion LeMans lug cracked in almost the same location. The lug itself split apart completely, not the brazed joint, about 1/4-1/2" below the top edge of the lug where the 'paint' crack is on your frame.

Since posting about it other folks noted their frames cracked in the same place.

Is this joint a common one to crack on frames or if not all frames, Centurions?

Al

The frame will not fail suddenly; you could mark the ends of the crack with a marker pen and check it each time you ride to see if the crack lengthens.

It looks like a crack in the brazing filler. To repair burn the paint first and clean with a wire brush. Add some brazing flux and heat with an Oxy-acetylene flame to an orange red. The brass should run together again. Use a brass filler rod if necessary. A local welding shop should be able to handle this.

Thats a paint crack......you can tell its in the paint just by looking at it. The paint looks thick there. If it is a crack in the brazing, its an easy fix, but will require fresh paint or powdercoat.

Thats a paint crack......you can tell its in the paint just by looking at it. The paint looks thick there. If it is a crack in the brazing, its an easy fix, but will require fresh paint or powdercoat.

+1 That is what I thought too when I looked at it. Good photos by the way. That glob of yellow paint above the crack may have something to do with it. There is a paint expert on BF, Dr. Deltron. I'd get his opinion.