Builds 79 Aussie BJ55 build

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So I rushed things when I pulled the two chassis ends together and skipped fitting some angle inside the chassis rail.. now I'm being kept awake at night because I think its there to stop the chassis rail caving at the lower arm mount..



Contemplating making some out of 3mm strap formed by the anvil and tacking them inside the chassis rail.. this means of course i'll have to seperate the chassis again now and reposition and measure it all up..

I'm wondering how much of an impact the 3mm plate on the inside/out of the chassis rail would help mitigate that bit missing and if its worth doing at all.
 
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Not a chassis engineer here either, but I’ve seen a lot of this done with half the effort you’re putting in here.
My .02 would be to “v” that seam and run a nice root pass with a pre-heat. Not sure if you cleaned the inside perimeters of the seams with an abrasive wheel, but that would help eliminate pulling contaminates into the weld.
After that, I would go with the fishplate design you made, with a couple exceptions. Put the weld-through holes on either side of the seam by a couple inches (several centimeters). That way there’s ample support on either side and the full meat of the plate covering the seam. And if possible, angle or round the ends to avoid 90 degree vertical welds.
But that’s me, don’t feel obligated.

*edit#6
I would also suggest scrubbing the seam with acetone before and after sanding the paint off prior to welding.

*#7
... as well as all around the perimeter (twice in one post) of where the fishplates will be welded. If you use any kind of weld-through primers (I’m sure you’re familiar with what you use) sand it back at least a 1/2” from the edge. I found some stuff recently that works way better than advertised weld-through primers, but if you’re not planning on using anything, that’s probably fine too😄

51F6DDA0-C06E-49D6-879B-BC4FD5834D24.jpeg
 
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My .02 would be to “v” that seam and run a nice root pass with a pre-heat. Not sure if you cleaned the inside perimeters of the seams with an abrasive wheel, but that would help eliminate pulling contaminates into the weld.
I've been bevelling my test peice and will do that with the chassis.. I didnt think to pre-heat the chassis prior to the root pass.. but playing around tonight I think I've finally managed to dial my welder in for the uphill run. Yes I flap disked the inside of the chassis rail prior to pulling the two sections together.

After that, I would go with the fishplate design you made, with a couple exceptions. Put the weld-through holes on either side of the seam by a couple inches (several centimeters). That way there’s ample support on either side and the full meat of the plate covering the seam.
Understood and I agree. I had queried the weld through holes with my engineer but am yet to receive a response. seems best to avoid it without his professional advice.

And if possible, angle or round the ends to avoid 90 degree vertical welds.
I had not intended welding the vertical edges of the fish plate but rounding the ends of the fish plate will mean I can weld the entire way around..

I would also suggest scrubbing the seam with acetone before and after sanding the paint off prior to welding.
I don't have any acetone so I'll try and source some (I'm sure the wife wont appreciate me putting a dent in her stash).

as well as all around the perimeter (twice in one post) of where the fishplates will be welded. If you use any kind of weld-through primers (I’m sure you’re familiar with what you use) sand it back at least a 1/2” from the edge. I found some stuff recently that works way better than advertised weld-through primers, but if you’re not planning on using anything, that’s probably fine too
I had tried to weld over the weld through primer and struggled to get a good ground so I'll spend more time removing all the paint when welding the chassis.. I did think to prime and paint under the fish plate and keep the weld area bare metal but weld through primer seems to be a safer long term solution.

@RUSH55, @sneaky and @scrapdaddy I really appreciate your suggests and feedback, so thank you. I think I'll cross my fingers and put my faith in the fish plates doing the job of the inner chassis braces..
 
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Finished welding the chassis tonight.. not the greatest but its the best I could do on my back under the chassis brace.. a few spots I ground back and re-did...

I took some prep and weld photos for the engineer but ill grind it all back when I put the fish plates over the top anyway.. all the side welds are uphill..



I'll try and get some better photos in daylight..
 
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