To weld or to not weld….

The stress cracks going the other way concern me. If you weld it, I wouldn't weld the crack. I would weld everything up solid including closing up the hole and redrilling and counterbore. 

Was it a loop out or a blow to the side? Normally most of the force would be pushing it together unless you are lifting it up on a stand or crashing. I wouldn't hesitate to weld it and feel safe about it. 

I have had mine on my 98 cr 250 fixed a few times, never an issue with the repairs.

New subframe. Not worth the risk imo 

what risk?

My repairs are so much stronger than org, that I have 0 fear of that failing.

If it’s stress cracks , what’s stopping a new one from the same thing? I’d contact KTM and see if they’ll do anything about it!  If not, Why not weld it with some added support for strength, then if it cracks again maybe new is in order 

Ahhhh you gotta love older ktm's and their home depot subframes. 

Umm failure of the subframe 

Plate it, weld it, then drill it out.  

I think it depends on your budget and how much you care about the possibilities.

Weld it. riders have the subframe cut or extended all the time.

Weld it and check it every 20 hours with crack detection spray. 

Weld it. It's an easy fix.

Ahhh you gotta love the fact that he's still enjoying a 16yo KTM that evidently is still running strong. 

Replace it.

That aluminum, is most likely something like a 6061 alloy with a T6 heat treat which makes it have somewhere around  a 26,000 psi yield. If you just weld it up you will reduce that area and the area around it down to basically a T1 which has around an 8000 psi yield.  

I’m picturing a large fellow seat bouncing, causing the subframe to bow out. Causing those stress cracks. Lots of people modify subframes with no issues. 

Just make sure whoever welds it knows what they are doing and it shouldn't be a problem.

Weld it. If you want to you could have someone weld a little piece of bar stock over the crack but given the stress on the subframe that could cause it to completely fail is compressive and the crack is not in that direction I would just weld it up. I am going to guess those cracks have been there for a while. If it was that highly stressed the subframe would have already failed.

Ain't broke. Don't fix it

That's a bold take on aluminum. On aluminum, the weld is weaker than the supporting material; steel is opposite. Those stress cracks working up are more concerning. With this being a notched mount, I would guess its only a matter of time being you see it re-cracking and continuing to fail. 

Weld it up, keep an eye on it and get a new subframe on order to replace once it starts to re-crack. Some things are worth risking, I wouldn't say this is one of them. 

Can't plate a notched mount lol...

No problem tig welding that. I'd run a conical die grinder along the crack to get yourself a good penetrating weld. Probably best to fill the bolt hole and re-drill and countersink. If you don't want to do that, plug the hole with a stainless fastener to act as backing for the weld. It's possible that bolt was over-torqued as well leading to the crack.

"Probably best to fill the bolt hole and re-drill and countersink"

Great idea!!!! hmmmmmmm

Mate, if you're happy with the bike, well, it's most of the 'battle' when it comes to riding.

Now, my bike was bought in 2002, and it's a bike that was basically a 1990 /91 model. But, I'm happy to have it Forever.

Mind you, last weekend I went out to a mates "Little Unadilla" track, on his property. Took the Old Teddy Bear of a bike, as he loves to ride it on that track.

He surprised me with a new 300SX sitting there. He'd insisted I bring my gear (I'm not riding much now - Both Knees and Hips utterly destroyed) . I'm glad I did.

Oh My. Late / Latest model bikes sure Are something.

Riding the 300 was just wonderful. Just a perfect bike, on a perfect, grass and loam Natural Terrain track. We also had a 23 450, 250F, and other bikes there.

The 300 was the absolute pick of the litter. I'd get one in an instant, if I were able to ride more. I dream of a modern 350- 400 2t, and the 300 may be somewhat near to what I believe would be  perfection. 

But, my mate spent most of the day on the 500, as, he loves it (I've willed it to him, but, he doesn't know that), and, on that track, set up for a Heavy Old Man, it works well for a Fast, Light rider. As does his bikes for me - an Old, Large and 'leisurely' paced rider. 

Anyway, to the Repair : So common on the Old KTM subframes. The Countersunk bolt 'wedges' out the aluminium. That, and other forces, cause that cracking from the bolt hole, outwards

I've repaired a few, generally by welding the crack, then plug welding the holes, then machining / linishing said welds flat, then welding a 3.125mm / 1/8" plate, of around 4 / 5" on top of it (with No finish weld Across the subframe) along the edges of the plate, and then using a Button head bolt and washer. I linish a taper to the thickness of the reinforcement plate going towards the rear, and, linish any weld overlap onto the plate, so as not to have any 'catches' for boots. Never had a repair come back. 

I think if you or a buddy is a legit welder then weld it… BUT if your paying welding rates I would buy a new one🤷🏻‍♂️🤷🏻‍♂️🤷🏻‍♂️