verktyg 

I think what you are seeing is residual paint that's lifted off of the metal rather than cracks. Scrape off the paint is those area and look for signs of cracks in the bare metal.

I'm jaded because I worked around high qrality welding in the aerospace, medical, food processing, semiconductor manufacturing and other high tech areas as well as heavy construction welding.

For those who may be unfamiliar with the terminology, metal welding almost always refers to heating a part or parts to high enough temperature that the material melts in the weld zone. A filler material made of a similar metal is heated to the molten stage and added to build up the welded area or fill gaps. The melting point of steel is ~1370°C (2500°F) but welding temperatures get hotter.

It can be done with a lot of different technologies including an oxi-acetlyne torch or various methods using electro-arc resistance welding with and electrical arc to provide the heat.

Brazing or soldering on the other hand uses metal alloys that melt at lower temperatures that the base metal and microscopically embed in the surfaces of the part or parts to create a strong bond when the brazing metal cools. Brass or bronze brazing alloys used on bike frames have a melting temperature of ~1500°F to ~1800°F.

Welding thin wall steel parts is tricky because it's easy to overheat the material and burn through the tubing.

The weld in question looks REALLY cobby. It appears to have been done with electo-arc "stick" welding rather than more sophisticated TIG (Tungsten Inert Gas) welding. Most welded bike frames are assembled with TIG welding.

As @dddd mentioned, it's easy for the lower meting temperature brass to contaminate the steel weld. My welding instructors would have beat me soundly about the head and shoulders with a bundle of welding rods if I ever did a weld like the one on this BB...

That said, the kludged repair may last longer than the rest of the bike... On the other hand, why did it crack in the first place? Overheating during the initial brazing is the usual culprit. Or... it could have been a defective BB shell to start off with.

Now that I've offended everyone with my OCD aesthetics...


The only spec that I could find for a late 80's early 90's Chorus BB length is 111mm. I'm running Campy 111mm wide Veloce sealed bearing BBs with Chorus cranks on a number of bikes. They're inexpensive and so far have worked well.

They come with British (68mm wide) or Italian (70mm wide) threads with steel cups and a solid axle, steel cups with a hollow axle and aluminum cups with a hollow axle.

Note 1: Once a crank arm has been installed on a BB spindle and used, the aluminum deforms and all of the crap about ISO, JIS and so on is just that! If it fits, IT WORKS!

Note 2: The Brits call lugless brazed frames "bronze welded".... The US and the UK, two peoples divided by a common language!

verktyg

Chas.