Poorly done welds, advise please

[rocky4by]

I'm interested in this offroad racing chassis, but the welds are pretty poorly done. It's all 4130 tubing, some tig welding and some looks mig welded, if you zoom in on some of the welds you can get an idea of what they look like. The photo that is the brightest, on the far right post coming down actually looks cracked maybe. Can most this all be cleaned upped and gone over with tig? Or should a keep looking, thanks for any information.

[Bushytails]

Some of those really look like they didn't penetrate at all... also looks like it's been welded on by different people at different times. But, as to how bad it is, and whether it's easy to fix, I'll let someone who's better at welding than I am answer.

[aametalmaster]

Unless it was cheap I would pass

[rocky4by]

Thanks for the replies. I know I should pass, but it is the right price as long as it would clean up and still be safe. New chassis are 2" now and are around 80/ 100k I can get this on for about 1/4 of that. Being 4130 it worries me what kind of heat its been zapped with. Attached is a photo of the same chassis just doesn't have the body on it. These are capable of about 125 mph and my son and I like to have fun but need to know are ride is safe.

[Bushytails]

Dunno, I'm more of a crawler fan... 1-ton axles with 5.88 gears, rear steer, 3-link or 4-link suspension, t-case doubler would be my type of buggy...

[Ltbadd]

That's a lot of welds to have concerns about when your life and others are possibly on the line. I doubt anyone could make an assessment just thru photos alone.

[ryanjones2150]

Man when I clicked on your post I was expecting to see some serious nonsense. Are those great welds? Probably not at the price you’re saying it is. But they honestly don’t look near as bad in the pictures as you describe in your text, but like mentioned, it’s hard for us to see in a few pictures.

I can at least say this, I’ve seen way worse get through the tech inspection at the drag strip. The only guy around here that “professionally” builds custom chassis doesn’t weld them that good.

That pipe cluster almost looks like it’s been welded with stainless, and that concerns me more than the appearance of the welds in your pictures. There are two reasons a guy would use stainless rod on that. First, he’s having trouble with porosity and instead of figuring out why and making it better, he’s leaning on the crutch of some stainless rod to get by. Second, stainless rod, especially 312, runs like butter and can make a hack weldor lay down some nice beads. Either way, it’s concerning. If those are full penetration welds using stainless, you run the risk of them cracking unless the backside of those welds were shielded. If they were, they’ll probably be fine. If they were not shielded, the backs are probably all sugared and nasty and they will crack.

These are not at all abnormal concerns when you’re buying a used custom chassis, but there was nothing in your pictures that would make me barf. By the looks of the construction, the fit ups look good. The angles look good. The coping looks good. If I saw poor fitups, I’d certainly have cause for alarm.

This is just my opinion based on a few photos though. I’d say trust your eyes and look at the overall construction to determine whether is been built by a hack or someone that took some pride in their work.

But to answer the question on whether you could just wash those welds in nicer with the tig. Yes. Generally speaking, with 4140 and 4130, unless the guy used 4140 rod, the heat treating wasn’t made brittle. The weld area is small enough that just welding a bit slower and letting it heat up good is plenty to keep it from crash cooling, which is the problem with chromoly you want to avoid. It’s not the heating up, it’s the cooling down.

Hope that helped.

[Bushytails]

The welds at the very top right of the third image concerned me the most... they look like zero-penetration booger welds to me. But, I'm not a great welder, so I may be wrong.

[Helios]

Are you allowed to MIG weld that kind of thing? I thought it was like a CrMo airframe, where it had to be welded with O/A or TIG to get enough heat into the welds so that they would "normalize" to some extent? Where are you getting cracking? On the MIG welds?

Is it "legal"/"allowed" to MIG if you immediately heat-treat the welds right after welding? As Ryan said, I believe it's the "quenching" effect you get -- where the workpiece effectively "quenches" the weld material, cooling it off too fast and thereby making it brittle -- if you don't put enough heat into the whole thing, which is what often happens with MIG (I believe this is why MIG welds on car body panels often get harder than the hammers of he||, and resist dollying afterwards...)

I have no idea, just regurgitating stuff I've read...from memory (which ain't great)...personally, I think I would "pass."

[MMW]

My opinion is yes you can reweld with tig. It is common practice to repair broken, bent, mangled race car chassis from accidents so why not this? Obviously it's going over a lot of the welds vs. a few but same principal. If something fails tech because of a few welds you fix them instead of scrapping the whole thing. Just my thoughts.

[ryanjones2150]

I went back and looked at that third picture, it’s hard to tell from the image, it’s a bit blurry. You can repair these things, like MMW said, just because it’s a race car chassis doesn’t make it magical.

I’m not aware of anyone mig welding chromoly, but you are correct, it does not allow for sufficient heating of the welded material to resist cracking during cooling. You would want to preheat the material, not post heat. You could post heat, but unless you have the torch lit and waiting for you, it’s a bit late because it cools very quickly being so small in comparison. I am also not aware of any place that will heat treat an entire chassis after welding, which is why it’s important to weld it correctly and with the correct filler metal, which is not 4140 filler wire.

Anything you buy in the racing world is a project unless you’re independently wealthy and can pay someone to do all your work. But I don’t think that’s what most people get into the racing hobbies for. If you get this chassis, or any other chassis, you will almost certainly need to make changes or modifications to it, so look at it like that.

But I still stand behind my statement about the stainless welding, that will be a lot of grinding out and rewelding in what is probably the toughest joint on the entire chassis.

[rocky4by]

Thanks for all the great replies, lots of good help and information here. I passed on the first chassis I posted about, just many ? with it and being 1.75 tubing it would also be hard for me to get it Score tagged. Anything over 4000# has to be 2 inch now, so I believe we're going with this one now.

[Bushytails]

Those look a lot nicer.

I'm surprised how many tubes one of those has... Is it really any lighter than a ladder frame?

[rocky4by]

I believe it's designed like they are because of how many ways they take an impact while racing and in a crash. There not light any more, 5800 lbs maybe a bit more or less. There holding 70 to 100 gal of fuel now and getting about 2 mpg

[Bushytails]

When I think of a tube buggy, I think of something like this company's products: https://www.fabn801.com/products I think they have about a tenth the tubes! lol

But, as I said, I come from the crawling world, not the racing world...