While doing top end rebuild i discovered cracks in the frame just behind the steering tower. Is this a common issue with these? What is the recommended fix?
I thought about adding gussets but in the end just welded the cracks up. I'll keep an eye on them.
You can't really see the cracks in the photos but the circles show where they are. This is after i ground them but before welding. The cracks went about 2/3 around the tube, all but the bottom 1/3.

 

Yes, I have welded up several 350s with this problem. If it persists, I have put triangular gussets inside, but you then have to cut away a bit of that white plastic tray that goes between engine and tank. You also sometimes get those top rail tubes cracking next to the uprights behind the tank.

Suzuki 450 to 750 King Quads crack in the places you indicate too, but they also crack/break far worse on the bottom tubes, most often next to the rear anti-roll bar mountings.

 

Good to know, I'll keep an eye on it. I suspect this wheeler had a rough life. Now it will just be used around my property so I don't expect to need as much maintenance.
I've rebuilt the swing arm, wheel bearings, carburetor, rear brakes were frozen, piston and cylinder and now just need to replace one front wheel bearing.