Colnago Mexico Super: sheared chainstay repair or replace?
 

I would appreciate some expertise advice whether i should look to have the sheared driveside chainstay of my Colnago Mexico Super repaired or replaced and recommendations for framebuilders who could help. thx

It's really hard to say without pictures. You can put them in your gallery. "Shear" isn't particularly descriptive. Is it cracked all the way around? Is there chain damage?

Sometimes it's possible to TIG weld a crack. Not sure it's a great idea, I would always replace the stay.

Thanks for your input. Will upload photos when permitted (need to reach 10 posts) You'll understand what I mean by shear when you see it.

Vancouver frame repair
 

Paul Brodie and Chris Dekerf are two experienced and excellent frame builders in the Vancouver area. I've had several repairs done by these two fellows.

Vcr frame repair
 

V

thanks for the recommendation. i checked in with Dekerf about it, his price seemed quite high from which i inferred he wasn't terribly keen however, would do it if i in$i$ted. haven't check in with Paul yet. Toxik Harald also recommended Ross Alan who's taken over at MacTalla; he is supposedly very experienced with lugged frame building and repairs however is inundated with the shop presently and hasn't setup a workshop for all his framebuilding tools.

Colnago chainstay repair
 

i know shear to mean exactly that: shear as in break off, break in half hence the eng. term shear strength.

anyway, since pictures are worth a thousand words, even a whole dictionnary full of them...sigh, Kermit's broken "frog" leg:

https://cimg6.ibsrv.net/gimg/bikefor...04aa948697.jpg
https://cimg9.ibsrv.net/gimg/bikefor...e15196fe68.jpg

I almost mentioned Ross as well, but I heard he was pretty busy with the store. I've seen a couple of his Bonavia frames and they look excellent. I've talked to him a couple of times about doing frame repairs, but we didn't line anything up. He seems like a good guy.

What scenario causes these failures?

Well, that's sheared in the colloquial sense, but it's the result of a fatigue crack from the bending loads. Clearance dimples have led to many fatigue cracks in chain stays. Chrome probably didn't help much either.

I would say there is no point in any repair other than complete replacement. Could be welded though.

Do I see chain suck evidence? The other aspect is the gap between the broken faces. The RH stay is now pulled back WRT the drop outs. If this was a result of an after failure force then OK. But if this is from the stay failing then there's some stress in that frame that was seeking release. Andy

As I understand it, the early Colnago Mexico frames (with round main tubes) did not have dimpling on the chain stays. The Colnago Super frames had the chain stay dimpling.

So, if your frame has round main tubes, then it probably IS NOT a Mexico.

That could well drop the value of the frame in half, and would impact the decision of repairing vs selling as-is.

Pictures of the full frame, and lug cutouts would help confirm the ID of the frame.

Is there any deep rust on the frame?

@CliffordK brings up an interesting point. I don't have a Mexico but I do have a Superissimo about 1983 vintage. It does NOT have dimples in the CS. I don't have a very good picture of the DS CS but it is the same as the NDS. The CS is ovalized. You can see it partly in this pic.
https://live.staticflickr.com/3820/1...3e42088b_c.jpgP1000501, on Flickr

Which is not anywhere near the same level of deformation of the OPS.
Here is a NDS pic.
https://live.staticflickr.com/3719/1...534c3731_c.jpgP1000521, on Flickr

Makes me wonder if someone dimpled the CS to accommodate a poor chain line due to the wrong spindle or using a triple, again with the wrong spindle.

No, the OP's bike has bike factory dimples in the stays. It's nearly inconceivable that was done after the stays were brazed into the frame. Your stays are round oval round, which is done by the tubing manufacturer.

I don't think I could get ROR columbus stays back in the '70s and early '80s. In any event, I have dimpled many round columbus stays, really hard to get a crank or tire to work otherwise. Might not be easy for the uninitiate to tell that the OP's stays are not ROR, but they are totally different.

Generally takes more heat to remove a brazed tube than it did to put it together ...
chainstay dimples get done at the tube mill ..





...

I would replace both with round/oval/round. ebay often has them. This one is for a guy who has been down this road before.
I think the stays have pins at both ends. If it was me doing the work, after paint stripping- off to the plater to have the chrome removed.
Chrome and hot enough to take things apart- toxic

Many frame builders tend to like to grind the pieces out/off rather than heating to remove.

Lots of flux, working outdoors, mask, etc, and one should be able to work around the chrome on the remaining parts.

My lungs have suffered enough from my stupid framebuilding adventures, I wouldn't braze chrome.

My health is worth getting the chrome stripped. due to the cast bottom bracket, chainstays don't usually braze quick.
I did reference today my three Colnago Supers, all three have indentations on the tire side of the chainstay. NO indentation on the chainring side.
Not to say Colnago did not do it, but, I would go simpler.

I have a couple of sets of these chainstays if who ever takes this on needs a set.