Broken 88 swingarm

[Texas30cal]

Another setback today, I started tearing into the swingarm and found a big problem. How common is this

[broken1]

When you loosened the cinch bolts the swingarm came apart like that? The break is so clean it looks like it was made that way

[Texas30cal]

Yes sir, when I stripped the bike down I just pulled the swingarm and set it on the floor, never turned it over 🤦‍♂️, you can see where the break is dirty and the small clean areas where it broke last.

[2ndmoto]

I have never seen that failure before

[Texas30cal]

Pics of the repair, I milled a bevel on it almost all the way through , still can reach a little more inside and going mill the outside nearly flush then put another pass on top. I know the swingarm was probably heat treated after welding and this won’t be but I’m not riding it like I’m 17 again either .

[The norm]

Yes that swingarm was heat treated after all welding was complete. I have seen several aluminum swingarms welded after they break or crack. I have also seen them extended both cast and fabricated. I don't know what happened to all of them, but some of them broke. I watched as a young man almost got seriously hurt when his modified aluminum swingarm broke.  I would personally find a good used aftermarket swingarm. I am not just spouting off here. I have 20+ years working in fabrication and welding. Welding that swingarm is like playing Russian roulette!
Loren

[Texas30cal]

I’ve got lots of years in machine shops myself and that’s the plan, I’m going to get it together and keep my eyes open for a nice replacement. If it had been the top side that was broken I wouldn’t have even attempted it.

[atvmxr]

i have never seen that.  usually its up front around the swingarm bolt

[Texas30cal]

I haven’t been around these for a long time but seen many others, I can’t imagine why this happened unless it was possibly a bad extrusion to start with.

[The norm]

The aluminum used for swingarms is not flexible for the most part. Steel and chromoly have a elasticity that makes them superior for swingarms, A-arms, and frames.  So if you think about the lack of elasticity in the aluminum and you think about the aluminum bearing carrier being difficult to remove. My first thought is that someone down the line put a little too much leverage on the carrier clamping are trying to remove the carrier.
All the aluminum that I have had to bend in my career has either been an aluminum that is freely bendable or I have had to anneal it before bending. Then after it gets formed the aluminum gets sent out for heat treatment.
Loren