Hi guys, I would like to replace a chainstay on a lugged frame for the first time. It’s a Colnago master competition. And i want to replace the drive side chainstay.
My plan was to cut out the old one. braze out the left part at the dropout, because it looks like the dropout goes into the tube? and grind down the left part on the bb lug.
After replace the new one with silver.
Any one knows wich columbus chainstay sticks inside?
Any tips for less heat damage of the paint?
I prefer to cut and grind the pieces rather than use more heat. There are 2 reasons:
1 - tubes don’t like more heat cycles and
2 - some frame joints are pinned and unless you know where they are pinned and want to drill the pins out, you risk tearing lug sockets as you heat and pull on the tube you are trying to remove.
3 - In your case it’s also important as there is chrome on those stays and fumes/vapor can be pretty harmful when heating chrome (hexavent poisoning). I’m sure the dust isn’t good either so wear an appropriate mask.
I’d cut the CS a few mm away from the BB Socket and then cut it 25 mm inward from the dropout. and then grind those both back until they are ready for the new tube. Then cut the new tube to fit and braze it into place ensuring the dropout position is where it should be.
One way would be to cut off the stay a cm or more away from the DO, then make the new stay butt against that cut, silver braze with a doubler (sleeve) inside, and polish off the joint so it doesn’t show. Brazing with rings of filler pre-placed inside will be easiest, clean, and complete penetration pretty much guaranteed.
@bulgie what is the likelihood that is pinned? Low I’m guessing. I might try to heat that out but the sleeve works too. I haven’t done that before so I can’t say. Either way it’s not pretty with the chrome vapors and paint damage it will cause. The sleeve is probably easier to get the length right. With the slotted dropout it’s not super critical anyway…
I don’t understand, what slot?
EDIT: Oh I see you meant the horizontal DO, yes that makes precision C-stay legth less critical.
Chances they pinned the chainstay to dropout are close to nil I’d think. A pin is more likely at the BB end but I wasn’t suggesting sleeving that joint, just the DO end.
Do you know of chromium vapors (fumes actually IIRC) being a problem with brazing? I thought that was welding only.
Yes, I got what you meant, I wasn’t clear. I edited my reply.
I have heard/read that it is a problem at brazing temps as well but can’t find anything specific on that. With chrome, I’m like a toddler when someone says ‘hot, hot’, I just don’t touch it. I don’t know what ‘hot’ means, I just know I don’t want any!!
I’m probably over cautious but as I get older, I value my health more.
Take the BB out (you will have to anyway) and have a peak inside the chainstay. You will be able to see the pin.
Edit: I stuck fingers in the two naked Colnago’s I’ve got in the shop right now (1981 super, 1984 superissimo) they as per my memory of others have pins in the main tubes, and fork crowns. but contrary to my memory; they do NOT have pins in the CS/BB connection
For silver-soldering/brazing, there isn’t much of a problem with chrome fumes. Plus, this is such a small area, and you are performing the operation once (well, once at each end), that having good ventilation, blowing away from you, will take care of things.
I agree, that the chainstay is very likely not pinned.
It is difficult, from your photos, to tell exactly what the damage is, that you are trying to replace the entire stay. Is it cracked?
It will be very difficult to save this paint. I have saved paint (somewhat) when replacing a rear brake/stay-brace by loosely wrapping a number of layers of crinkled, heavy, aluminium, foil around the surrounding area, and doing the braze with as little heat and as quickly as possible. In your case, since you won’t end up with a chromed chainstay, you’ll need to paint it anyway. So, I would just make a trip to a hobby shop (or auto finishes shop if you happen to have one nearby) and pick up some matching colors.
I’ve used alu foil for areas a bit farther from the braze, but for up close to the braze I prefer Heat Fence, a clay- or putty-like stuff in a jar, that you mold around the part. Actually the one I’ve used lately is called Wet Rag™, same stuff, funnier name. Pretty much infinitely reusable, just put it back in the jar, maybe sprinkle some water on it if it got dried from the heat.
Of course in a pinch you could use an actual (lowercase) wet rag. Also reusable.