Replacing chainstays on a lugged frame bike
 

Is it feasible for a skilled framebuilder to remove existing round chainstays and replace them with oval chainstays to improve tire clearance while improving stiffness? The bike is a 1978 Trek. Eutectic 1810 low-temp silver alloy brazing rod was used to braze the frame, back in the day.

you could use round oval round chainstays. Anything else would require major revamping of the BB shell. Anything can be done, somewhere on Bilenky's site they have pictures of replacing a BB shell with an eccentric bb shell. I imagine you would find this surgery to be too expensive though.

Not sure a narrower chain stay (having been squished to oval either by the factory of by the builder) will be stiffer in the pedalling directions. (Also not sure how much a stay's wall thickness relates to pedalling stiffness, the rear triangle is a triangulated structure unlike the main triangle where the tubes lay on the same plane). Andy.

OP; 1) technically it should be possible to indent the chainstays on the tire side without removing them from the frame to give you the bit more tire clearance. This would involve make a set of dies (see the thread at the top of this forum for the "show us your work" or show us your builds). You would need to make a die for the round outside to keep its shape and make one for indent on the inside. Then you have to find something to push the inside die into the chainstay while it is held in the outside die. Figuratively I am having a mental picture of a "jaws of life" like hydraulic device... something strong enough but small enough to still fit in between the stays and allow space for the inside die. There should be something to do the job.

2) More realistic; I would recommend seeking someone currently owning a touring version of the Trek who is looking for a bit more of a racer style.... then just figure out how to convince them to just swap frames with you. Baring success there, just buy a touring trek off Craigs and sell of the racer trek if you no longer want it.

To get the BB shell hot enough to pull the tube out, you may change the bond ,
of the other 2 main tubes.. as that will also be at melting point.

A couple of C-clamps?

Unless you cut off the CS at the end of the shell's socket and then grind out the remaining CS. Depending on the fit of the replacement using Silver might be able to be used for the rebrazing.

But this is a lot of work for more clearance. before I'd suggest replacements I'd indent the origonal CSs. A simple rounded form of the correct diameter pressed into the CSs should do it, as mentioned. I don't think a hydrolic press would be needed. A big hammer is how I'd start. Andy.

IIRC, these Treks were pretty well dented to start with, so I'm not sure how much more clearance you are going to get with that approach. You can get a chainstay into most bench vises, so that's the approach I would take if I wanted it to look good. Using appropriate cauls, obviously.

See here for procedure:
http://alexandchristine.smugmug.com/...P1080110-M.jpg

I've successfully indented chainstays to increase tire clearance. I fabricated a die out of a short round piece of bar stock about 3/8" diameter brazed to a plate, and semi-circular cut in a block of plastic for the outside of the chainstay, and used a 3" narrow-jaw vice to press the die into the inside of the chainstays, covering both with small pieces of leather to keep from marring the paint. It worked beautifully. Added a good 5 mm more clearance on each side.

This won't increase the stiffness, and may require some cold-setting to realign the rear triangle afterwards. It's easier with high-ten chainstays.

Yes, I spoke with a frame-builder who suggested denting the chain-stays and re-alignment of the rear triangle. He had a frame on hand that he had dented and the workmanship looked good. I'm seeking 4mm greater clearance, just 2mm on each stay. The existing chain-stays are round and the material is Columbus SP. The job should go well. I'll post before and after pics later this month.