er, the bb is cracked, not cracked apart. you cannot clean inside a crack unless you open it up. that means the stress riser remains.
A fine bur on a Dremel tool makes quick work of prepping a crack for repair by brazing.
well, you can cut the crack out and refill the hole i suppose, but it wouldn't be as strong. and seriously, it would take extraordinary luck and inordinate messing about with a crack without opening or removing it to clean it sufficiently to guarantee a good properly wetted join down into the crack itself. without that, you're just lipsticking the pig and the stress riser remains.
I reckoned the thing to do would be open, clean, and flux the crack, but not stop at filling it to the surface. I'd use a 45% fillet forming silver wire and build up a decent 10mm or so fillet. That should let the material in the surface of the fillet take a lot of stress off the underlying steel. If brazed steel frames couldn't tolerate flaws and irregularities on the insides of the joints, they'd fail a lot more often. Most of them, lugged or filleted, are pretty ugly in there.
Welding over a silver braze, or any braze for that matter, is a Welding 99 error - predictable failure. To this specific bike: If it is cracked all around, he may be able to get reasonable alignment which will eliminate the stress on the joint which caused the crack. If so, as Chalo notes, a cleaned simple butt joint silver brazed with full penetration should be adequate. Regarding that type of crack see also: http://www.yellowjersey.org/zito.html
!Jones said:
Yeah, I'd have to see it; however, I'd give odds that the frame is dead. I once tried to repair a BB shell and it was an unmitigated disaster. The guy had forced the cups into the wrong sides and musta used a big cheater. I tried to build it up with a tig outfit and rebore it... one of those ideas that should have worked, but didn't. I was trying to do a favor for a friend and he ended up threatening to sue me for a new frame. Although, what that has to do with the current case, I haven't a clue.
TIG isn't the best choice as you'll need much effort cutting threads across the various weld layers. I'd wonder about the brazed joints nearby depending on total BTUs over time(?). We fill in bronze for that. Here's an extreme case. The BB machine work was yesterday afternoon: http://www.yellowjersey.org/mitch.html
The classic Brit frame repair shops (Jackson, Hetchins, Holdsworthy) at one time slit the BB shell, pressed the edges together, welded a seam right across the shell then cut new threads in the smaller bore. Some postwar bikes had steel threaded rings brazed into the shell on both sides. A steel sleeve could be similarly brazed into a reamed shell then properly cut with piloted taps I suppose. Regarding your BB story, don't be discouraged. A few hundred 'charity' jobs on BSOs will get you a better range of experience and you meet some nice people that way. -- Andrew Muzi www.yellowjersey.org Open every day since 1 April, 1971
a farmer might find a suitable tube, cut in half, cut top in half, cut snd file hole/slots for top half's tube bracing, file/grind/hammer tube to fit BB, clamp, tig tube, tig tube end to BB ends.
Yes, he might. Farmers are famous for making worn-out pieces of [censored] last another year or two.
Amazing not just what you can do, but actually what people can afford to have you do for them
That page is a bit short of 'commerce' And my employees learned basic techniques on projects like this where the standard for 'victory' is low. -- Andrew Muzi www.yellowjersey.org Open every day since 1 April, 1971
TIG isn't the best choice as you'll need much effort cutting threads across the various weld layers. I'd wonder about the brazed joints nearby depending on total BTUs over time(?). We fill in bronze for that. Here's an extreme case. The BB machine work was yesterday afternoon: http://www.yellowjersey.org/mitch.html
"Today our customer said his headset felt funny. He tried to adjust that bearing . . . to no avail "
The Raliegh looks like it spent time on the SF waterfront with exposure to ocean spray and fog.
It's been ridden daily for work and errands over 30 years in humid Madison WI through all seasons (one of our local seasons is 'road salt'😉 and lives out of doors. -- Andrew Muzi www.yellowjersey.org Open every day since 1 April, 1971
