Little Jap trail bike frames are not all that robust especially when they get hammered by lads a bit too big for them. Tube on this Yammy was 1mm thick and gave way on both back legs due to the spreading force of the horizontal shocker.
White line (vertical in this pic) is the swing arm. Blue arrow is the shocker. Frame broke between the two reinforced sections...
Cleaning the old paint out of the crevices as well as off the tube and gussets took almost as long as welding... important to reduce contamination of the weld and resultant weakness.
To keep the frame still looking fairly original I reinforced it with 25x6mm bar on the inside of the frame tubes. They were bent to conform to the existing frame: some of the bends as welding proceeded. Principle to keep in mind is that we have extended the new reinforcing to and past the existing gussets. Taking it just to the edge of the gussets would still leave a weak point. Now the whole section that is stressed by the spreading action of the shocker is fully strengthened and it is unlikely that the frame will ever be broken due to this action...
The lad's dad did some light moulding and after painting reckons it looks "a million bucks". Main thing is that repaired section will stand up to any punishment it is given because it was done properly...