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Engine Bay Frame Rail Butt Weld Opinions


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So now that i finally have my chassis level and where it needs to be i can begin my rust repairs. In the engine bay i have removed all of the deeply pitted metal from the battery tray and am left with this.

Datsun 12

Datsun 6

I have a new zeds findings engine bay frame rail in my possession already but i would really prefer to not have to re locate my sway bar and front crossmember mounting locations as well as my tc rod box since this section of the frame rail only had minor internal pitting. My idea is to por 15 the inside of what is left of the original frame rail. After it is treated and painted i would brake up a piece of 16g a sheet metal to the internal dimensions of the old frame rail and the new 6" back or so of either side of the location of the butt weld. I  would then drill multiple holes at two different distances on either side of the seam which would allow me to spot weld in those locations. Finally i would butt weld the seam between the old and the new rails. After all this i would think the seam would be just as strong if not stronger than the rest of the rails. But this is my first body work and frame work experience ever so I'm hoping  to get opinions of those that have experience with this. I am a good experienced welder it is just the idea i am looking for opinions on thank you.

 

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6" on either side of the butt weld, so, 12" total? Honestly, I think a 4-6" piece (2-3" on either side of the butt weld) would be more than enough. To answer your question, I think you have a good plan, and I doubt that it would ever fail. Mind you I am not an expert by any definition of the word, but I think I have a decent idea of what would or would not make a suitable repair.

 

Edit: Not sure about POR-15 though. I know it's a popular product, but IMO a lot of people use it in situations where it's not really the best option. Whatever you use, make sure it's something you can weld through/near. I'm thinking a weld though primer with zinc would be a good alternative... but do some of your own research on that.

Edited by rturbo 930
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So if I understand your explanation, you are planning on making an insert to the old frame rail and then drilling through both the frame rail and the insert and spot welding, then finishing off with a butt weld on the outside with the replacement rail slipped over the insert?

 

That is going to look real nice.

 

I'm a little skeptical of using por-15 in the area to be welded. I think the fumes would contaminate the welds pretty quickly. 

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Perfect thank you for all the input guys, I finished my battery patch panel tonight I'll weld it in and fix the frame rail on Thursday. As for the por 15 idea my reasoning for using it was because it adheres directly to rust. I will not be able to prep the inside of the frame rails so I was not aware I had other options. Also I didn't think the por 15 would contaminate too much since it will be on the inside seam of the spot welds and butt welds. But I have never worked with it before and I definitely do not want my welds to get screwed up. I do have some weld through primer in a aresol can, but that will not work for shooting all the way down the rail. If you guys have any suggestions of products or application techniques I would love some ideas. This is my first rust repair project so I'm still a newbie.

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Por15 will smoke when you weld near it and become almost tar like if my memory serves me correctly. They have some flexible nozzles that you can attach to spray cans to reach areas further away. I suppose the inside of the frame rail further in could benefit from the por-15, but I think the immediate area near the weld should have maybe zinc primer at the most. 

 

When welding something closed, I noticed the smoke liked to roll around, as I got close to closing it off it would come up and cause some bubbling of the weld on occasion.

 

I do get the concern of closing something off leaving the inside untreated. 

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Do not use POR15 in a welded area.  Use a zinc weld through primer like this:

http://www.amazon.com/3M-05917-Weld-Thru-Coating-II/dp/B0015PG4E0

After you are done with the frame section, drill a small hole in the bottom or use an existing hole and spray the inside of the section with this:

 

https://www.aircraftspruce.com/pages/cs/primers/zinc.php

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Thanks for the heads up seattlejester I will make sure to drill a vent hole before I weld the rail closed. I have been using zinc weld through primer in any location of welding. The area I really wanted the por 15 is in the front section of the frame rail where I cannot reach with an aresol can. If I did this I would leave abou 4" from my welds with no por 15 in these areas I will be able to use a wire brush to prep and spray with weld through primer. Thank you for the product recommendations john c I will purchase those as soon as possible. Does anyone see problems with using por 15 in the sections of the frame rail where I will not be welding? There is already surface rust in there and I need something that will adhere directly to rust since I can't prep the inside of the rails, I also need a product that will treat the rust so the rails will not eventually rust through.

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I wouldn't worry too much about that vent hole, there are lots of other vents in that rail, no way it will build up gas pressure. I just recently repaired the same section of frame on my car. 

 

I just weld through primer on the backside to prevent flash rust. Later I intend on going back and using one of the zinc phosphate inner frame coatings with a wand. 

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The only way to stop rust is to physically remove it.  POR15, Zinc phosephate, etc. will only slow it down.  Its taken 40+ years to get some surface rust on the inside of the frame rails so even if you did nothing you've probably got 20 years before rust through.  I'm never been a fan of POR15 because it makes a mess of any future repair.  I prefer zinc phosphate or zinc chromate or some kind of phosphoric acid/tannin rust converter.  

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Not only does por 15 make a mess of future repairs, if you don't have perfect surface prep and adhesion, it can accelerate rust. This is because it is an impermeable urethane that will hold any water that gets between it and the steel. It will maintain its integrity with itself,effectively hiding the failure from view.

 

Based on my research, I would use an epoxy primer or zinc phosphate /chromate as John suggests, followed with cavity wax (applied after welding).

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