Engine Bay Main Rails, Repair or Replace?

[Sanchez]

My 240Z has succumbed to dreaded front sway bar cracks and rust along the main engine bay frame rails while I was at college. Now I have the time and money to straighten up the chassis and I was hoping to hear from the community their suggestions on whether these rails can be repaired or whether it would be better to order a set of rails from Zedd Findings since I’m already buying their floor pans. I am aware that these spots can be patched easily but my main concern is that them being open for a long has allowed the entire inside of these frames to start rusting and they will slowly deteriorate if not fully replaced. I will add that I do have access to an excellent body shop that always cuts my dad a good deal when he brings cars in.

[ISPKI]

That is definitely repairable on the surface but be prepared to have to replace at least twice as much as what looks rotted. Fortunately, that rot is forward of the engine cross member so I doubt you will have any structural issues. The inside can be extremely difficult to access, damn near impossible in alot of cases. I did a ton of repair work between the firewall and the cross member and I actually ended up cutting out the bottom of the frame in a long segment to make sure I got most of the rust. After welding in fresh coated steal, I drilled a hole open in the frame and sprayed in rust reformer, let that set up for a few days and then hit it with internal frame coating.

 

Opening up the bottom of the frame all the way back to the firewall will give you access to the inside and let you determine what needs to be done. Fortunately, the vertical sides are what carry the load here, the bottom can usually be removed without compromising structural integrity as long as the motor is out of the car, which it appears to be.

 

I would just assume that you will have to replace the entire bottom of the frame from half a foot forward of that rot all the way back to the firewall. It slopes down towards the firewall so if any moisture was trapped in the frame it would accumulate towards that area most likely.

[grannyknot]

What @ISPKI says, I'm going to bet the bottom of both those rails are pretty far gone. You can replace the bottom with 14-16ga sheet metal and add a bit of strength.

[ISPKI]

On 5/10/2020 at 6:50 PM, grannyknot said:

What @ISPKI says, I'm going to bet the bottom of both those rails are pretty far gone. You can replace the bottom with 14-16ga sheet metal and add a bit of strength.

Ya know mine in my 77 280z were actually not that bad!, I replaced a couple feet on the outside and about 10 inches on the top but the only area on the bottom that was rotted was right around where it met the firewall. The rest of the bottom appeared pretty OK all the way up to the engine crossmember. There is a divider piece inside the frame over in front of the firewall that was rotted out on mine which was extremely difficult to replace. Doing 1 panel at a time, taking your time and dont try to replace everything at once should keep that frame structurally sound, especially having the engine out of the front. My car is so light without the motor that I reposition it by lifting the nose and shifting it around my shoppe by hand.