What is the best way to tackle this rusty area in my firewall drain?

I've got the wire wheel onto it, and used the protec metal/rust conditioner product a few times on it.

Do I need to completely cut it out and replace? I hope to treat the rust further as best as possible keeping what's shown in the pictures in tact (structurally), MIG fill in holes with new metal as required, and weld in a new sheet of mild steel over the top in the engine bay side.

Here is another pic..

Yes. It will be a better repair, and will most likely be easier. You'll be forever "chasing" the holes if you try to fill them with weld.

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1970 ex Group A Rally P510
1971 P510
1972 180B SSS
1965 SP310 Fairlady
1966 SP311 Fairlady

+1 for a total replacement.
New metal for old is best.
Cut the old making sure you get the edge back into decent metal, i.e. non rusted.
Then weld in the new patches from zinc annealed sheet building from the inside out

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Regards, Graeme
Just trying to help...
http://nissanman.shutterfly.com/
graemes@internode.on.net

Thanks for the advise guys. I have some mild steel sheet ~1mm thick so will get busy using that. Just going to be a bit of a pain welding from the inside of the cabin, in and up under the dash.

Its not an area which gives any real structure to the car (datsun 1600) is it? If there are other opportunities to strenghthen anywhere in the engine bay, please let me know (as i'm doing an SR20det conversion and just repainting the engine bay area).

I have seen the use of 'H beam' angle welded into the guard area on various build threads. Does anyone know how thick this shoud be?

Cheers,

Of course there is seam welding throughout the engine bay... is there anywhere I should avoid seam welding?

So many questions!
Replace that rust. It won't be as hard as you think. Doesn't give "heaps" of strength to the structure, but metal is metal. It all ads up. Doing the SR conversion, i would keep the outside plate off. I found that when i put my SR in, there was no clearance there with the fitting kit i used, and had to panel beat it in, So really wasn't worth keeping there afterall.
To strengthen the front A arms, I used 75 x 25 rhs and cut that at the angle and welded it in.
There are pro's and con's to seam welding. Basically if you seam weld, you should do it everywhere along the car and in all the little places as the seam welding in one area will only distribute the force to the area that is weakest.
I personally didn't seam weld with my SR conversion for the road. However, gave the front end some decent strength with the top rails to A pillar brace. In process of making my strut brace. And I have thicker sills also.

That's all I have so far with the strength side of things.

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Ongoing Project: 1972 Datsun 510 S13 SR20Det. http://ozdat.com/forum/viewtopic.php?f=33&t=17898
New Daily: D22 Navara (The new workhorse)
Retired 12/2016: MY98 Subaru Impreza RX
Previous Car: Restored Green 1972 Datsun 510, Hot L18

Cheers Ross.. hmm this topic of seam welding is an interesting one. I must read more into it but just thought i'd do some in the engine bay while i'm re-painting it. I'll repaint the rest of the car at a later stage.

By the way, I have the Datsport SR fitting kit. Which kit are you using where you experienced the clearance issue?

Datsport kit also. At the firewall drain bit that you have already removed which held the brake dist. Block. Heater pipes hit that i found.

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Ongoing Project: 1972 Datsun 510 S13 SR20Det. http://ozdat.com/forum/viewtopic.php?f=33&t=17898
New Daily: D22 Navara (The new workhorse)
Retired 12/2016: MY98 Subaru Impreza RX
Previous Car: Restored Green 1972 Datsun 510, Hot L18

Ross, please check the engine mounts are the correct way around.
The mounts are offset & if not correct will space the engine back further.
There is an easy fix for the LH heater pipe.
What clearance do you have at the rear flat section LH side of head to the firewall.
Should be around 25mm.

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A little knowledge is a dangerous thing.
www.datsport.com

"R.I.P. Baz. 29 April 2022. Thank you for all your contributions to the Datsun community over the years. You will be missed." - OZDAT

I removed the sheet metal cover to gain a little more clearance. Plus it also stops big gum leaves and crap from getting stuck in that area and rusting out the car further!


+eleventy Bazilllion for replacing the metal with sheet metal.

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1972 Datsun 1600, S14 SR20DET Engineered (204rwkW @ 17psi.)
viewtopic.php?t=6579
#SR20Datsun @SR20Datsun

This one is an easy fix, take your time, maybe experiment with some card (I use manilla folders for work out some basic shapes) Make sure you replace it though.

Cheers,

Trent

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1600 Build: http://ozdat.com/forum/viewtopic.php?f=59&t=22694

+1 for card/cardboard etc.

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1972 Datsun 1600, S14 SR20DET Engineered (204rwkW @ 17psi.)
viewtopic.php?t=6579
#SR20Datsun @SR20Datsun

Unless the engine mounts need to be swapped left to right and vice versa, mine are fine. Pulled the engine out of my half cut, and promptly installed it straight into the Datsun. At first the pins on my X-member didn't locate properly so the engine was sitting up, but once installed and it popped down into its locating pins it was fine. It cleared the back ok now (I think but still very tight fit).
The clearance from the flat section (the bit with the bolt hole in it that sticks out off the head) is approximately 30mm. Whats the fix for the left hand heater pipe?

_________________
Ongoing Project: 1972 Datsun 510 S13 SR20Det. http://ozdat.com/forum/viewtopic.php?f=33&t=17898
New Daily: D22 Navara (The new workhorse)
Retired 12/2016: MY98 Subaru Impreza RX
Previous Car: Restored Green 1972 Datsun 510, Hot L18