Frame patch question.

[TylerN]

My disco used to be a V8 and there is a rust hole in the frame where the catalytic converters used to super heat the frame. It’s not huge, but I’d like to take care of it before the salt comes back.
Are there any special considerations that I should have before attempting this? (As a novice welder..).
Can I just take a piece of 3/16” plate, cut it to a curved shape to avoid long stress welds, prep and patch?
Or should I find a ticketed welder to do it?

[TylerN]

This is the spot.

[landcrabmechanic]

I would be concerned about how far that corrosion goes into the frame, have you taken a chipping hammer to the frame in the area around the rust hole. You may find very thing metal a ways away from the hole. My idea would be to cut the rust out, weld in a new piece, then plate over top in the curved shape you are talking about.

[camo388]

As stated see how far the corrosion goes and cut it all out. You might be lucky enough to have patch above rolled corner of the frame. Radius the corners of the hole and cut the patch for a tight fit and weld in new material. Depending on the thickness of the frame, make the patch same thickness or only slightly thicker but only by 1/16". The patch will be flush to the outside of the frame so the extra thickness won't show. You can't make the patch too much thicker than the original frame otherwise you can not fuse the two thicknesses properly as you will be blowing holes in the thinner material while trying to melt the thicker plate. Make the patch a tight fit to the hole as any gaps are harder to fill when welding thin material. Tack weld the patch all the way around, every 1 or 2" so there is less chance of warping. Weld a couple inches then skip ahead a couple inches then weld again a couple inches. Welding this way means you are welding cold material and less chance of blowing a big hole when your welding area gets too hot. Once you have been around whole patch allow it to cool then go around again filling in the gaps. Be sure to overlap second weld into first welds. A start and stop without overlap will tend to give a weak spot as the welds don't fuse into each other. Once you have welded all around patch, you can grind weld flat and cover patch with larger plate. If you see any flaws as you grind, just make a long weld to cover the flaw and grind again. The weld has to be fairly flat otherwise you will have trouble getting cover plate flat enough to be able to weld to frame. You want this cover plate to be larger by 1/2" or so all around so it's weld is in new frame material and the cover plate weld isn't on top of the patch weld. You'll probably find you need to hammer or clamp the cover plate tight to frame as you tack in place. The cover plate should be big enough to cover the bend otherwise you end up with a weld at the bend and it becomes a weak point. I hope this all makes sense. I've been a journeyman welder for 35 plus years so easier for me to just do it than to write it out. And before you ask if I'll come and give a hand, I live in Alberta.

[TylerN]

Thanks for the great reply camo388! All of what you said makes sense.

[camo388]

Hello Tyler, If you don't think your welding is good enough to do the patch you can do the prep work and then the welder just has to weld. Be sure everything is clean as any paint, tar, etc., will just corrupt the weld. Once welding is done then you can paint and or tar all you want as road salt will eat away bare metal in no time.