EVO has landed

[Thunderchild]

The new to me Evo arrived today.    Bittersweet.  The initial frame inspection revealed a possible crack on the down side of the head tube down tube junction.  See the pictures below or in my gallery.  The crack might be hard to see.  I had to take several photos.  It is the line along the edge of the weld.  I can't imagine the frame flexing here; cracking the paint.  Any thoughts on how severe this may be. It looks like it is along the weld if it is a crack.  Anyone know of Evo frames cracking here?  I am not opposed to having it welded; I will just need to negotiate with the seller. 


 



Thanks
Thunderchild

[Thunderchild]

Just rising above the spam.   

Thunderchild

[shovelon]

Well there is where it would crack. Have see more cracks in the headtube themselves, so the headtube is good.

Terry

[Thunderchild]

No other cracks on the head tube.  I probably would not have seen this one if the paint was darker.  It is a high stress point, so is it worth welding?  The frame is 7000 series aluminum.

Thunderchild 

[Luke]

Hello heroic sunken battleship !
Um, the sunken bit is applicable here. Can you post/send a higher res photo?
From my considerable (see signature) experience of catching cracks in time to save the guarantee, that’s definitely a crack. (oh yes, I’m a mechanical engineer too)
Sorry about that.
You won’t see any cracks in the head tube itself, it’s so much thicker than the down tube that other bits go first.

That’s why I ride plastic bikes now.

You could get it welded up again, but it’s not that simple. After welding, the frame is put in an oven not only to de-stress the weld area (heat affected zone) but also to age the aluminium up to just before its optimum strength (horrible word that). You have to de-stress your weld, but in doing so you will take the alloy beyond optimum, thus weakening it…
IMHO you should cut a pair of nice curvy lateral gussets out in such a way that the loading isn’t simply transmitted to weld at the end of the gusset, but dispersed along its length.

Your other option is to do what a friend did with his BMX handlebars: source a roll of 20-30 mm prepreg carbon fibre strip and bandage, putting a strip around the front like a gusset in between each layer of strapping. Finding an oven to cure the carbon is going to be easier than for the weld (lower temperature).

Or you could just buy an OZ/5500 ;-) soo much more forgiving and you can fix them with a bit of glue.

Just please don’t ride it in that state, It would be sad if we were to lose you from the forum.

Good luck.

Luke

[Thunderchild]

Thanks for the comments Luke.  I took the frame to a builder.  He is going to have an ME who can TIG aluminum look at it.  If they do it, they will heat treat it as well.  One question about your comments.  What aluminum gets over fatigued, the new weld or the existing frame?  I will suggest the gusset idea.  The pre-preg carbon wrap also caught my attention.  Would you wrap it around the down tube and head tube?    It would look cool...   I could mold little wings on the sides of it as well...

Oh I almost forgot.  I have an Oz.  The stable needs and Evo too. 

Thunderchild

[shovelon]

No other cracks on the head tube.  I probably would not have seen this one if the paint was darker.  It is a high stress point, so is it worth welding?  The frame is 7000 series aluminum.

Thunderchild 

7005 is the easiest to weld. A simple root pass,, followed with a wash pass, with mandatory cooling  between passes is sufficient. The Easton technical PDF will give additional proceedures. 5356 is the filler alloy. 5183 is better if you can get it. I can send you some if you want.

6061 is the tricky alloy. Weld too hot=detemper. Weld too cold=overaging.

Either case don't put any load on it for at least a week.
Terry

[shovelon]

Luke, you must be the cracked frame KING!

Your warnings are well recieved. All alum frames make thier maker some day.

Terry