BMX frame repair..

[robwizard]

So I'm sure this has been asked before and I have just read a load of threads about it all over the place with no conclusive answer..

Can a 4130 Chromoly BMX frame that has cracked be repaired? Presumably the answer is yes.. but what is the best way to go about it? A couple of years ago I repaired a snapped brake lug in a Chromoly BMX frame, it had snapped completely off and the guy was gonna have to send it back to the USA for warranty repair so I said I would have a stab at it. I cleaned it off real nice, clamped it down, welded it using a stainless rod of some sort and wrapped it up to stop it cooling down too quick (which probably did nothing.. but was worth a bash) anyway it's still holding on strong and being ridden pretty hard, and I'm not amazing at TIG welding so did a I just luck out?

I ask because a friend has asked me to repair his frame which has broken on the chainstay with a tiny little crack. My plan was to again clean it off, drill tiny holes in each end of the crack to stop it spreading, then weld it again with a stainless rod and maybe put it in sand or something to let it cool slow?

Tips, advice, suggestions all on a postcard please!!

Cheers

 

[GrahamGKD]

Does this thread help?

 

[pedrobedro]

Brake lugs are usually brazed onto bike frames. You don't need stainless to weld 4130 ordinary ER70S2 will do it just fine. Just weld slowly with a longer down slope and let it cool naturally is the recommended way.

 

[citizen kane]

Unlike your previous repair to the tig welded brake boss you cant easily remove corrosion from a crack without removing a significant amount of material. The correct way would be a new chain stay but I doubt it would be easy to source.
BMX frames are usually plain gauge so it should be possible to buy in the correct size and gauge of 4130 stock.
There is no need to control the cool down of thin gauge cromo, the less heat you put in the better so weld fast.
If your just going to smoke it shut it will probably be OK, just keep an eye on it.