All the fish plates I have seen have been welded on and I've seen some big fish plates on some BIG excavator booms. I second the preheat, allowing the weld to cool slower will keep the temper of the steel better, keep it from getting brittle.....at least that's what I have learned. If it's not cracked into the flanges you'll have to stop the crack at both ends if it has not reached an edge. Usually done by drilling a whole at the end of the crack. Good luck with it, I'd weld it if it was mine, find a good well know welder of course.

 

It is an easy fix, go to a welding and fab shop or a truck frame and/or brake shop that has someone over ten years old that runs the place. They can fish plate and weld it in about an hour.

It will not meet the industry standards for the frame crumple zone, but that will be your choice and the frame/brake shop may have you sign a waiver saying you instructed them to fix the frame.

If you are half skilled at welding, you can fix it yourself for about $10 worth of 5/16'" plate and $3 worth of wire or rod. Just go slow, keep it just at a 30% penetration, and keep the slag off the weld. Weld the plate at the top and bottom of the frame where it turns to the rail, and not vertically across the face of the frame at all. Then seal the front and back of the plate where it is not welded with a good sticky undercoating material to keep the water and rust out of the open contact surfaces. A pro will probably weld it fully, but they also know how to pull the penetration and relieve the stress risers so the frame does not break at the front or back vertical welds.

 

It is not real clear in the pictures but the control mount that is welded to the frame is cracked as well I did not get under to investagate too closely to see complete detail. I will repair if insurance is unwilling to cover because they think the crack was defect vs incedent or if they total and I neg a purchase back and salvage.

 

the reason i say to make the fish plate oval shape is you can weld it all the way around without having a verticle weld....... i've done frames before