Chassis reinforcement? (crack)

[FinnCobra]

Have you stiffened your chassis? I prepare car for engine swap and during disassembly I found a crack. I have welded subframe connectors and strut brace. K-member original cobra but supported to front of subframe with stiff pipe. My car has zero rust. It has rather solid suspension. Front control arms are stock. Rear control arms has aluminum/pom bushings, and steering rack too. Pom is bit harder than delrin. We have autoslalom championship in our club, similar to your autocross. I participate in it, 5 races in a year, and several track days too. It is maybe the cause.
Any pics what you have done?

 

[SlowSVT]

The fender aprons in this car are pretty flimsy. I would think this may happen with coilovers but I can see your running the OE type springs. The other side is not affected just the passenger side?

The thing you need to be concerned with is just welding the crack will likely result in it cracking again as the metal adjacent to the weld will be hardened as the load that caused this is still there. I would make a pattern out of cardboard and experiment with various methods of reinforcing the area adjacent to the crack. The trick here is you don't want to go overboard and over stiffen that section all you will do is create a stress riser on either side of the reinforcement inviting another break. I would make the pattern just big enough to spread the load where it cracked to a wider area and make it out of .040" thick mild steel sheet metal about 1 1/2" - 2" square. You may need to bend it to follow the contours of the metal. Use weld-thru primer and spray it on the inside of the fender apron to prevent corrosion from the factory paint being burned off during the welding process. Make sure it gets MIG (or better yet TIG) welded and not "arch welded". Clean the weld best you can and repaint the area.

You can post pictures of your cardboard pattern on the fender apron for a 2nd opinion before you transfer that pattern to the sheet metal. I don't hang out much in the SN95 section so you will need to PM me a "heads-up" and I'll take a look.

 

[Blown_By_You]

I wouldn't consider that a crack at all.. I'd consider it a tear.. Just weld it up with some hardwire and you'll be fine..

 

[SlowSVT]

I wouldn't consider that a crack at all.. I'd consider it a tear.. Just weld it up with some hardwire and you'll be fine..

This statement has merit. If this was caused by getting torn by some outside force and is not stress induced just weld it up. If it's a stress crack that's a different story.

 

[FinnCobra]

It is on both sides. The factory cut where the crack is looks like it is for purpose. Maybe to control collision formation. But I don't like the idea that point that connects front damper to chassis has crack between.
I thought I'd cut rails to panel and insert steel pipe with welding. My friend drives rally with his Mustang and he removed that panel piece and replaced it with steel frame.

 

[Blown_By_You]

Whatever floats your boat man

 

[SlowSVT]

Finn

Chances are those are stress cracks. Look at them again they look pretty minor. Drill an 1/8" hole at the very end of the crack (called a "crack stop" of all things) and just have a MIG welder lay a bead along the crack, paint it and be done with it.