Z28 exhaust manifold crack opinion

[KevinW]

So I have these smog manifolds for well over a decade, probably bought at a swap meet. Original smog tubes on them, never been apart (till now) and original looking rust. Just getting around to cleaning them and found a crack, so disappointed.

Drivers side rear bolt hole, is it fixable? should I fix it? Crack does not appear to go into the bolt head surface. I have to clean the other and see if that has any issues

Any opinions? thx

[firstgenaddict]

I have heated cast iron exhaust manifolds in the oven on broil that were hot enough that it did not crack when I welded on it so it can be done.
You won't be "chasing" across the part, so you don't have to drill the end. Though if it were mine I may drill and pin that the piece - prior to heating and welding.

[KevinW]

thx. I have been reading up on the Nickel MIG products for cast iron (hot method). Using a BBQ grill (which goes up to 500 deg). Also there is a cold method of MIG too. I have a neighbor who is a TIG expert, I will hit him up for his opinion (don't want to give him more work! ). I think I have another non-smog manifold that is cracked similarly to practice on.

[BCreekDave]

Depends a bit on how much you want to hide the fix. If you don't want the outside casting welded you can V the crack on the face that mates with the head and weld that up. Then machine it back flat. Then bore out the bolt hole about 1/4 to 5/16 oversize and lightly press in a very slightly longer steel sleeve. The sleeve will take the stress of the torque on the bolt and the french lock will hide that its been sleeved. The weld will keep the crack from propagating further.
If you aren't worried about looks, it can be V'd out along its length and heated and welded up. You will still need to take a cut across the surface where it bolts to the head.

[KevinW]

Hmm, sleeve-ing it is an interesting idea. Its the rear drivers side and will be tough to see under booster and master. So I am not too worried about looks, some grinding and manifold paint will lessen the weld. Thx

[Unreal]

The car from which I made my Yenko tribute had factory A/C, and I wanted to retain it, but still wanted it to "look factory", Since the the 840 heads were missing a boss for one of the cast iron A/C brackets, I fabricated a bracket extension to bolt to a manifold bolt, and had it welded to a correct b/b cast iron bracket. It worked, but the fabrication looked obviously welded on. I ground/filed the weld marks off the part that did not look cast, and then, with a corner of a file, "pinged" it several thousand times. I then sanded it to sort of soften the ping marks. The result was almost indiscernible from a sand casting, especially after I painted it with Cast Blast.

[KevinW]

So what did you use for welding the boss on?

[Unreal]

I didn't weld a boss onto the head, I welded a 1/4" thick extension to the A/C bracket that picked up the two bolts on the manifold at #1. I was just saying that I pinged the weld and the top part of the extension, to mimic cast iron

[KevinW]

Right, I understand now

[big gear head]

I've TIG welded cast iron several times using N99 nickel wire, pre heating and then allowing it to cool slowly. Nickel wire is very expensive. I've laid coarse sand paper on cast parts and hammered on the sand paper to give it a cast appearance. Using a knurled breaker bar handle to hammer on parts can give a cast appearance.