Bicycle Mechanics - Broken Frame
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10-14-09, 06:45 PM
Hey guys, this is my first post in these forums. Hopefully someone can help me.
My bike frame (an older racing bike, from the early 80's) recently broke. It occurred along the bottom of the rear part of the frame (the part of the rear triangle which is parallel to the ground), right where it meets the dropout.
Is this irreparable? Could I weld it?
What's the material? Some pics would help.
If it's metal, then most likely it is repairable.
10-14-09, 06:57 PM
It's the chainstay. You could cut out the old one and weld or braize in a new one. Do you have the training to GTAW or gas weld in the new part?
10-14-09, 07:07 PM
Do you have the training to GTAW or gas weld in the new part?
And to answer the earlier question, it's made of steel alloy
Somewhat chancey to weld bike tubing absent a VERY experienced welder. Replacement chainstay
tube is ~$10 or so eg: http://www.cycle-frames.com/bicycle-frame-tubing/ROAD-STANDARD-CHAINSTAY-OVAL-22.2-DIAMETER-420mm-LONG.html
New tube could be fitted to the bike in a fairly straight forward fashion, brazing/silver soldering at the
dropout and mitering and welding at the BB. Some risk of heat distorting the BB exists. Results likely
to be better than welding the cracked tube itself.
10-14-09, 08:25 PM
Whether or not it can be easily repaired really depends on where the break is. This fracture occurred very near the chainstay-to-dropout brazed joint and was repaired for $50 by framebuilder Paul Sadoff of Rock Lobster Cycles in Santa Cruz. He machined a "V" notch on both the inside and outside of the fracture, then welded (not brazed) a bead on both sides and ground/filed it flush. It has held up well. The frame is a 1987 Schwinn Paramount with SL/SP tubing and Shimano forged dropouts.
Can you post a close-up of the break?
10-14-09, 09:56 PM
Uploading the pictures...
The image of the green bike... it's almost in the exact same spot, but it is a complete separation.
10-15-09, 02:36 AM
That's a fairly easy repair. You should also get the dropouts aligned afterwards to make sure they're parallel. Out-of-alignment dropouts are a major contributor to those kinds of breaks, and broken axles as well.
10-15-09, 04:01 PM
Here are some pictures of the break... finally :)
10-15-09, 04:53 PM
The frame should be repairable, but those other cracks make me think it might be better to replace the dropout instead of welding it. You can also post in the framebuilder forum.
10-15-09, 05:14 PM
That's definitely repairable, but like DannoXYZ says, the dropouts need to be made parallel.
Whomever does the repair should attempt to get the dropouts as close to parallel as possible and held in that position with a fixture while performing the repair so that any post repair cold setting to get the dropouts precisely parallel doesn't put undue stress on the repair.
Parallelism can be checked before and after using the Park Tool FFG-2 (http://www.parktool.com/repair/readhowto.asp?id=40).
10-15-09, 06:20 PM
If that frame is chrome-plated, that contributed to the crack. The acid-treatments and resultant hydrogen-embrittlement that occurs from chrome-plating tend to collect and concentrate at the tight angles, nooks & cavities of the joints.
10-15-09, 07:37 PM
From the looks of the weld I'd say it's been repaired once.
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