Thread: Welding An Aluminum Bike Frame?

So I put a crack in my Transition frame, right below the seat collar. The good news is I'm getting a deal on a new TransAM frame via warranty, the bad news is I won't get it until late June.

In the mean time, I got a guy at work with who can weld and he says welding the crack shouldn't be a problem. On the other hand I've heard mixed things about welding aluminum after its already been welded.

What's the verdict on this?

How far past that crack does your seatpost go? I'm assuming not far if you cracked it in the first place, so maybe get a longer seatpost in there and see how it feels?

^^^ the seatpost would still only be supported by the clamp above the crack though.

If you re-weld it, you'd need to re-heat treat it, otherwise that whole area will be waaaaaay weaker. There's a reason that aluminum frames are very rarely repaired.

True.

Through bolt it? IDK, frame is fucked anyways...

The guy at Transition said to just hack off the frame above the seat tube and put the seatpost clamp above the weld, but if I hack it off there wont be enough to material for the clamp to sit on.

I don't have much to lose by welding it.

How do your ballz feel?

Hack it and JB weld something in there. It won't look pretty but you could make it work.

Originally Posted by VTsession

The guy at Transition said to just hack off the frame above the seat tube and put the seatpost clamp above the weld, but if I hack it off there wont be enough to material for the clamp to sit on.

You could hack it off, put a collar on the seatpost, to keep it from sliding down and tack the collar to the frame to keep the seatpost from lifting out.

That would put a lot less heat stress on the frame, although I never got the impression that bikes were heat treated after welding. I've also never built bikes.

You would probably end up cracking the tack welds at some point, but it might make it a month.

Originally Posted by toast2266

If you re-weld it, you'd need to re-heat treat it, otherwise that whole area will be waaaaaay weaker.

This is correct. Get real, ride steel.

Sincerely Yours,

The Lo of Curtlo

ETA: This failure is almost certainly resulted from a seatpost that was too short. A seatpost must penetrate to at least 2cm below the entire top tube/seat tube junction.

Originally Posted by krp8128

True.

Through bolt it? IDK, frame is fucked anyways...

yeah - the frame's fucked, and if your only goal is to salvage it til you get your new one, hack it off at the weld and drill a hole straight through the seatube and post. Tighten it down, while being careful not to crush the tube. If you drill the hole at a point moderately low on the seat post, it shouldn't affect the post at all for future use.

Originally Posted by Big Steve

This is correct. Get real, ride steel.

Sincerely Yours,

The Lo of Curtlo

ETA: This failure is almost certainly resulted from a seatpost that was too short. A seatpost must penetrate to at least 2cm below the entire top tube/seat tube junction.

seatpost was actually stuffed down when it happened, I was hitting a series of jumps.

my new frame will be steel.

Welding without heat treating is not good BUT I would cut that cracked piece off ,file it flat,use a good collar and keep a very close eye on that area

you DO want to make sure you got lots of seat post in that seat tube

Thru bolt, as mentioned above. I've run a frame this way for a few years now. Mine originally broke a bit higher on the seat tube than yours, so I had a little more material to work with, but it hasn't failed after a few DH seasons.

If possible, use two bolts, and run the bolts in from the rear of the frame. Perhaps tap the forward wall of the tube if you can't get nuts and washers on it? Then use lots of loctite and go easy on the torque. This will keep the junction 'immobile', or at least reduce the strain that could cause the aluminum to fatigue.

Originally Posted by shimstack

Thru bolt, as mentioned above. I've run a frame this way for a few years now. Mine originally broke a bit higher on the seat tube than yours, so I had a little more material to work with, but it hasn't failed after a few DH seasons.

If possible, use two bolts, and run the bolts in from the rear of the frame. Perhaps tap the forward wall of the tube if you can't get nuts and washers on it? Then use lots of loctite and go easy on the torque. This will keep the junction 'immobile', or at least reduce the strain that could cause the aluminum to fatigue.

I like the thru bolt idea. I'm going to have to welded and add a couple thru bolts to reinforce it. I'm going to have buy a cheapo seatpost, I'm not putting holes in my Thomson.

Thanks for the input.