DIY Engine Crossmember...need some feedback

[buening]

Its been awhile since I've been on here, so I thought I would update you on my latest workings on my mach. Recently there was a Cobra Automotive Crossmember DIY thread on the VMF, where a guy got ahold of the 65/66 crossmember dimensions and posted up the end bracket drawings. I tracked down the 67/70 crossmember and got the dimensions on the end brackets as well. So with that, I've decided to get my butt in gear and get mine fabricated since I've been putting it off for nearly 2 years! A little background.....I dropped my motor 1" and moved it to the rear 1.25", so the stock crossmember no longer fits nor will the stock CA crossmember. Rather than purchasing and hacking up a $200+ crossmember, I'm making my own. Below are a few drawings with two options. Both utilize 1.5" x 2.5" x 3/16" angle iron end brackets and 1.5" x 1/8" wall steel square tubing for the center tubes.

Option 1 is the stock CA type which requires you to cut a slot on the angle iron and bent the horizontal leg down, in which you weld to tube to. My tubes approach that bent leg at a larger angle than the stock CA crossmember due to my lower oil pan, and with only one side of this angle welded/braced I have a small concern about the outer face bending. A simple gusset would fix this.

The 2nd option, is simply removing the bent angle leg and extending the tube onto the vertical face of the angle. The hatching is the fillet weld. I drew in a 1/2" ID (1 1/16" OD) SAE washer with the bolt shoved as far as it would ever go, and I have 3/8" clearance from edge of washer to the edge of the tube (not including fillet weld). The tube has a radius at the corner, so the fillet weld will likely be minimal. I also won't need a continuous fillet weld, so I could probably stop where the washer would get close.

Option 1:

Option 2:

Closeup of End Bracket on Option 2

So, which do you think looks stonger and/or easier to fabricate? Looking for ideas of improvement or just general feedback! I know I'm approaching super overkill for a mostly street car, but when I do something I find any weakness (at least in my mind!) and make it better. Option 2 isn't as aesthetically pleasing, but this isn't a show car and few will ever see this crossmember. Eccentric eliminators will be utilized between the LCA mount and crossmember.

 

[B67FSTB]

From all I know and have read your options ........and my poorly english....
I think option 2 looks better and you have room to put a wrench on the bolts for tightening.
Just the welding has to be very good to be a strong crossmember.
just my 2eurocent

 

[stangg]

Option 2, and you could always "notch" the tube where you need a little extra clearance. The notch could be a simple curve (large radius, not too deep) once cut out, just form an 1/8 plate to conform to the radiused notch and weld it in. You won't lose any strength that way and still get plenty of clearance.

 

[cmayna]

+1 for #2

But more importantly, using StangFix labeled pictures on the Vintage Minivan Forum is very awesomeness :thu

 

[Anonymous]

Option # 2 looks mo betta to me.

 

[buening]

But more importantly, using StangFix labeled pictures on the Vintage Minivan Forum is very awesomeness :thu

Their photo gallery sucks balls, as it has a max of like 5 or 6 pictures per person (last time I tried anyways). I haven't had any complaints over there with the Stangfix-labeled pics, so I'll continue to use it with the benefit of promoting this site as well :thu Now that its owned by a corporation and not Bob, I doubt there will ever be any fuss.

I too was leaning towards #2 (obviously since its what I came up with), but figured I'd throw the two ideas out there for discussion in case someone finds an issue that I may have overlooked. I'm definitely open for other ideas or areas of improvement.

 

[Anonymous]

Another idea would be for you to make ME one!

 

[buening]

You mean to tell me you are racing around with that dinky stock crossmember under there? Thats gotta be worth a few seconds on the track :char

I gotta work on my welding skills before anything gets fabricated, its been a few years since I've picked up a mig gun! I just got a new-to-me Lincoln Power-Mig 255.

 

[66benchcoupe]

Option #1 looks stronger to me. It will also be less likely to 'pull' when welded than option #2.

On your tubing try to get 100% penetration and do not grind the welds flat.

Robert

 

[stangg]

Option #1 looks stronger to me. It will also be less likely to 'pull' when welded than option #2.

On your tubing try to get 100% penetration and do not grind the welds flat.

Robert

I think option 2 is stonger simply because the distance between the bolt hole and down tube is closer... hence less leverage being exerted on the weld... it should be a shorter more direct load path and better distributed with the weld surrounding a good portion of the tube.

In addition to not grinding the welds flat, anytime you're butt welding thicker materials, you should grind an angle in to the mating butts to form a V. The V gives more surface area for the weld to penetrate and a flatter bead.

 

[buening]

My issue with #1 is that any forces transferred from the end brackets to the center tubing will go through the bent piece of end bracket, which is only supported on two sides....one side that is welded to the vertical face of the end bracket and the top side where the bend occurs. Adding a gusset would make it more stable with it now having three sides of the bent piece supported against bending. With #2, the forces are transferred through the two side welds and the top leg of the end bracket. I'll also be welding the backside of the bracket to the tubing (dashed/hidden line in the drawing).

Regarding the welding, the side welds will be along the radius/corners of the tubing. Anyone have experience welding that? I'm thinking I'll need a bit thicker weld to make up for the corner

 

[stangg]

Not a thicker weld, but multiple passes... or you could run a bead on the radiused corener first, then grind it square so that when it's installed on the flat you've just got a 90 degree fillet to weld. It really depends on how deep the fillet is. I'd probably just run a bead to fill the deep cavity first, then immediately follow up with the final fillet. The first bead will act as a preheat and help the second bead flow better. It sounds like your new welder will easily handle this.

 

[66benchcoupe]

My issue with #1 is that any forces transferred from the end brackets to the center tubing will go through the bent piece of end bracket, which is only supported on two sides....one side that is welded to the vertical face of the end bracket and the top side where the bend occurs. Adding a gusset would make it more stable with it now having three sides of the bent piece supported against bending.

#1 would be stronger with a gusset. The reason I like it better than #2 is that there's less welding on the part and I think the tube would be stronger welded all the way around the miter in #1 instead of top bottom and 2 sides like #2, if that makes any sense. Have you considered getting a piece of 1/8" wall 1-1/4" OD round tubing formed instead of welding the tubing together?

Regarding the welding, the side welds will be along the radius/corners of the tubing. Anyone have experience welding that? I'm thinking I'll need a bit thicker weld to make up for the corner

Your 225 should be able to burn a 3/16" fillet into that radius easily. You could notch a face off the tube so it would fit flush with the 1-1/2" leg of the angle. Make a jig when you weld it and clamp it down. Push or drag all welds (heat) towards the ouside of the part. If it pulls you can straighten it by heating and quenching, but not too hot!

Robert