Z28 exhaust manifold crack opinion
 

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

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.

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.

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.

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

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.

So what did you use for welding the boss on? :)

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

Right, I understand now :)

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.

Thx, I talked to my neighbor and he has used the nickel stuff before. Just need to arrange for a fix try :)

OK, my neighbor only has the nickel in stick format. So I went and bought this NI55, only $63 for 2# at local McMaster-Carr. For that price it is worth a try (same stuff $80-$100 on Amazon). I have a bunch of rusted manifolds that I can practice on :)

I will try the "cold" small puddle method first, then the 100 Deg small bead 2nd, with ping plannish the welds. If neither of those work, then I will try the full heat in BBQ for 400 deg, weld full and slowly let cool for a day. Fun!

I would be curious to know how this comes out as I have a cracked manifold on my original 69 Z-28 that I plan to repair. My guess is that some preheating and slow cooling will be required to prevent a brittle high stress weld area and to keep the weld from cracking in the future. Remember the manifolds are subjected to large thermal stress cycles of expansion and contraction in normal driving, probably what cracks most manifolds in the first place.

Paul

I would pre-heat it weld it then put it back in the grill & use the grill to bring the temp down... or make a sand heat sink to weld it in then cover it with sand to cool slowly....

Also I would Tig weld it only because you can control the heat easier ...

Gas welding with cast iron filler is another option. Indy Cylinder Heads has a special oven that they use to weld cast iron while it's hot.

I have been thinking about what I have to use. I do not want to bother my neighbor with TIG or stick, he has enough work to do! The MIG wire has an 45% iron core and 55% nickel cover. I have a BBQ grill, propane torch (small and large) and a bucket of sand.

After reading some sheets, recommended pre-heat is 350 deg (might need new gloves!). and end drill the cracks.

I have to weld a hole in a heat riser, so I will try the propane to get it up over 100 deg (some videos found about that temp), weld it, then in the sand. My shielding gas is mild steel mix argon75/CO2-25. Sheets say argon95/HE5 or argon75/HE25, but Helium is used to raise the temp, something we do not want here, so I will try the CO2 and see if I get good penetration.

For the real repair, I will have to wait for the ambient air temp to improve more (its still cold in the garage), before trying larger repairs.

It is just annoying to wait for spring, I wanted to finish up this smog restore months ago! :( Its been one set back after another. Smog pump was tricky to de-vane, two smog tubes rusted on, bolts rusted on, now this crack. At least the pump is done, and got the smog tubes nuts out.

Now I need to repair two nuts on one smog tube, still get the lower bolts out, fab manifold plugs and after crack fix, evapo-rust the manifolds and coat.

Well, not much is happening on the welding try. I have been gathering "stuff" and waiting for warmer weather. Plus spring is here which means tons of yard and garden work :(

I did make a box and immersed the good manifold in Evaporust. Strange thing was this yellow residue on the inside. Was able to wire brush it off, but it looked strange. Anyone else seen this yellow?

Looks to be Sulphur deposits, likely from octane enhancers used by refineries.

Kevin,

I am glad you are using welding material for the USA. The stuff made in China is junk and will never provide an adequate weld. You should also make a jig to mount your exhaust manifold in so that when your done welding the holes in your exhaust manifold lineup with the threaded holes in your head.

Chances are you will have to drill the bolt holes out a little bigger on the end cylinders #1 & #7 anyway, those style manifolds always seem to shrink in from heat.

We used to see that sort of cracking on similar design exhaust manifolds from mid 70,s Chev trucks that had propane conversions.

Hmm, that might be tough. I have to cool this down slowly, so overnight in a bucket of sand is the ticket.

I have been working on the smog tubes and the un-cracked manifold. Once done with that I plan to switch to the nickel MIG wire and try it out.

Thanks for the tip. I will test fit the manifolds and see how they fit before welding. I can always hit the bolt hole with a die grinder.

Very hard to die grind that length of hole, just use numbered bits and drill it slightly larger till bolts go in if the manifold has shrunk.

Most of you probably know this, but there was a repair station at the Tonawanda Foundry for cosmetic welds on cast iron parts. These repairs could only be done on non-stress areas though. The repairman just heated the damaged area to cherry red with a torch - then welded the damaged area - then covered the repair with asbestos cloth. They left the asbestos on until the next day before grinding the repaired area smooth. Most of the repairs involved chipped valve cover rails on heads and intake mating surfaces on the front and back of blocks.

OK, sorry for the delay. Family stuff came 1st in priority :)

So I wanted to fill a hole in a riser for a blank. Here are the pics. Had some feed issues partway through, so some crappy welds. But good news, a cutoff wheel took the welds down with no issues.

Did a dollop of weld right on the cast surface (previously media blasted). Could not pry it off. Then did some grinding and smoothed out nice without any cracking that I could see. Did some chip hammering and it dented easy.

Then I filled the hole, no pre-heating of cooling. That amount of weld did not heat the part that much. Ground it smooth, easy-peesy :)

Next, will have to make a crack in a junk manifold, drill it and bevel and see how it goes.

Alright! Lets work on an actual crack! On a test manifold :D

Drilled some holes at the end of the crack, but later saw it go further, so grinded past.

Cut a groove and ran a bead. Then put it in some media to slow cool it.

My feed issue is fixed, but I was not centered in the groove and it missed one edge. But still weld stuck well in the groove IMO.

Will still need grinding and some more passes, but I am happy with the result. Pinged it with hammer and it rang well.

I think I will next fix the smog manifold over the weekend and finish this test one up after.

Well, that was a FAIL! Weld looked nice but did not adhere. Ground it flat, hit the edge of the manifold and the cracks appeared. Well this is why we test :)

Did the first pass over an inch, too much probably. Next test will be 350 deg preheated, only 1/2 inch passes, then stress relieve, then back in the heat. Also instead of 75% Argon, I will be going full Argon and bumping up the heat range of the welder.

What are you doing to stress relieve?

No stress relief, just welded and stuck in media to cool. It was a test :) next test will include relief with pick hammer.

I'll pass along what we used to do at the mill when working with super hard brittle material. Try peening the weld with the pointed end of a chipping hammer. Just keep hitting it until you figure the entire weld has been gone over. Then do your slow cooling. It worked for us. Good luck

I am giving up on this :( Pre-heat, small welds, peening, slow cool. All did not work. So disappointed. Anyone have a non-cracked 3942527 manifold they are not using? :D

FWIW the exhaust manifold with the "raised walls and rivet bosses" for the preheat shroud and without the provisions for smog are not correct for any 69-73 Z28.

I had a similar crack on a small block manifold but was on the portion that bolts up to the header pipe. I never repaired and had no issue with it all.
I have about quit messing around with 50 plus year old exhaust manifolds and have been purchasing the repros. The casting numbers in most cases are correct, and the date code can't be read when the manifold is on the car and its nice to have a part that has not heat cycled dozens of times. Just my .02 worth.

I was just using this "other" cracked manifold as a test candidate. I have a SS350 4-speed, so it uses the same smog manifolds as the Z.

Buying a repro might be the way to go now and just use the one original side that is still good.

Thanks - I kept thinking to myself "I swear the crack was not near that bad".

The only alternative I can suggest is brazing the crack. Braze, while not as strong as weld, is pretty forgiving for cracks on cast iron since when the cast iron cools it will "stretch" to the surrounding shrinking iron rather than pulling the iron. You can ceramic coat it afterward to cast iron color (I've had good luck with Cerakoat Glacier). I've seen punch press frames brazed together that have lasted for years afterward. The manifold would be much less stress than that. Typical heat on the manifold is less than the melt point of braze. Maybe worth a try.

Thanks Dave. I think I have some brazing rods left over from another project to test that. What can it hurt? :)

Kevin, there is a guy up near me that knows how to weld cast iron. His name is Steve Babinsky from Automotive Restorations ([email protected]) (908) 236-6400. His cars go out to Pebble Beach. You might want to talk to him about the cast iron weld. He told me the cast iron welding rods you buy are from CHINA and are junk. He has his welding rods made here in the USA.

OK, I said I was giving up, but I just can't let a smog manifold go unrepaired :) So was doing some other tests and welding different cast iron stuff.

The "special" nickel wire was just not sticking to the parent metal. So in the "what the heck" moment, I just used the regular .025 mild steel wire. It seems to stick much better and don't see a join crack (yet).

So I went ahead and did the smaller of the cracks on the smog manifold. Its heat and clean 1st. Then when warm to touch, small beads, and grinding, then another bead and grinding, etc, waiting for it to be warm to touch each time.

Seems to stick properly. Finished it up with some die grinding and media blast. I will let this sit over night and then heat it up with a torch to see if any cracks appear.

Not sure why I am getting the voids, I ground them out between welds. I found after the first beads that if I start the weld on a grinded bead it flowed to the cast iron better than starting on the iron. I will work on the mating surface more if and when I do the 2nd crack. That will get a gasket anyways.

Opinions welcome as always :)