does this exhaust maniold look cracked or destroyed or am i ok?

[chewychevy67]

Passenger side 67 small block. I Needed to heat up the center smog port plugs pretty hot to get them out. I don't recall if it looked like this or not before heating but pretty sure it didn't. It looks like squares in the manifold where the rest looked like even cast. Would this be weak now? I am going to get these ceramic coated but don't want to waste my time on a bad one. your thoughts? any way to check it without putting it on an engine? Rod.

[69chevytrucker]

looks like spider cracks wouldnt worry right now

[old Chevy guy]

Don't know if you did that or not but Ive had some that were cracked that had that same crinkle appearance in the same areas. Not sure where to get more with smog holes in them though. Didn't know they came that way that old.

[mechanicalman]

Is that the side with the "hot air" tube that goes into the air cleaner? The housing routes air across the manifold and into the air cleaner under cold start conditions. Manifold gets hot quick while cold air moves across making the iron cold on the outside, hot on the inside so the uneven expansion causes the cracks. Even in Arizona this happened to my truck, after I removed the "stove" housing that enveloped the manifold on that side (so long ago, I think driver's side?) the new manifold never cracked after 20 years then I installed headers. Air Injection Reaction could only make it worse but not sure if that can cause it.

Is that a California manifold? If you can't find a new one, you can lay a layer of braze on top of the cracks and it should be fine.

[chewychevy67]

No 67 does not have a tube to the air cleaner pipe. That started in 68. This is the passengrr side manifold. This is going to be on a show & go vehicle so I may just get a new one. Would be a mess to change after it is all installed.

[Lee H]

A frequent sight at my local Pick-A-Parts.

[Hawghauler]

Both of mine were cracked on my '67. The passenger one finally gave out, broke off, landed on the starter. Took a minute on the side of the road to work that out so I could get home. These manifolds are famous for cracking. I remember in my youth (70's) hearing about not getting the '67 manifolds because of cracking even back then.
I went with headers.

[special-K]

I had one blow out coming down the long grade off of the north rim of Grand Canyon. I always figured it was fatigue. I figure it was cracked and that whole grade was either free rolling or braking. When I hit the flat and hit the gas it sounded like crap. There wasn't a hole,like that picture. It was all expanded like it exploded

[Steeveedee]

It's a common problem, not just one year. I've seen it mostly when the truck was used with a camper or towing. It is a change in the crystalline structure of the cast iron due to heat, and thermal cycling. It isn't helped by an exhaust system hanging from the manifolds (broken straps on the mufflers, for example). I'm not saying that your exhaust system is hanging, only that the breakage of the manifold is accelerated by that. I've seen them broken clean off the manifold, with the head pipe intact on the manifold flange.

[special-K]

I had one crack all the way around where it collects. It broke clean and dropped away going over a rough bridge. Before that I didn't her a leak. That was likely due to poorly hung exhaust over rough roads by the previous owner...by the way the rest of the truck was.

When mine exploded out at Grand Canyon I just had custom dual exhaust made before I left. The stock exhaust was in excellent shape,like the whole truck. That truck was babied by the previous owner. I limped it back to a muffler shop in Flagstaff. We couldn't find any manifolds so he put headers on and had to cut and weld doglegs on my brand new exhaust...bummer. The good news is that exhaust and those headers held up from '89-'04.