The Stovebolt Site Forums The Shop Area Engine Shop '56 GMC 270 manifold question

I am in the process of cleaning and painting parts as I prepare to reinstall my rebuilt head. I don't think the intake and exhaust manifolds have been separated for 56 years. Has anyone taken these apart and if so, how many broken studs/ bolts were there, if any? I am especially concerned with the two bolts. The nuts look like the gas wrench will work easily. The bolts appear to thread into the intake manifold body.

I have a chevy, but it is probably very similar, mine came apart easily, but I can see the potential for easily snapping one or two.

Dave,

Why do you want/need to separate the manifolds?

On the Chevy manifolds assembly, the two upper-inner bolts have nuts that usually come off OK. The two lower outer bolts, the ones you are concerned with, are the ones that are likely to break.

I am in the process of separating a 235 manifolds assembly. I have the carburetor studs easily removed, the two upper nuts easily removed, but the two lower bolts worry me. I am repeatedly squirting them with penetrating oil and repeatedly heating them with a propane torch (I do not have a hotter torch).

Be careful, and good luck.

I had the same issue with a 270 manifold. Try heating the intake manifold just barely red hot with the gas wrench in the vicinity of the bolt holes. It worked out OK for me with no breakage. Good luck!

My brother swears with this process to remove rusted bolts and nuts. He uses it on his old Model A parts. Once the rusty parts have sat submerged in the process for a while he pulls them out and the nuts and bolts come apart easily without tools. i don't see why it wouldn't work on the manifolds except they have been subjected to higher temps.

Hi, Tim,

I had a valve job done, and brought the manifolds to the machinist. The exhausts were an even and consistent 1/64" shy of the intakes, but he felt that in machining the gasket surfaces we might take a deep chip out of an exhaust manifold port/opening due to the rust, so he recommended trying it first as is before machining (it was all sealing fine when I took it off- the old if it ain't broke don't fix it). Then, I thought that maybe if I separated the two they would line up better. I ended up not separating and using permatex hi temp copper rtv on the exhaust manifolds. I'll see how it works tomorrow.

Dave

Sounds good, Dave.

I gave up separating the two lower nuts that hold the Chevrolet manifolds together. I used a pneumatic cut-off tool to cut off the nuts. easy peasy. The manifolds are now safely separated.

Now, I have to remove the two lower studs.

My manifolds needed to be separated so that the intake manifold can be used with a two-barrel AA1 Holley carb, with Fenton exhaust headers.

In your situation. I have used two sets of manifold-to-head gaskets. But, it looks like you are good to go.

Let us know how it works.

Hi, Tim,

It did not work. As it turned out, I cocked an intake to head pilot ring, so I had an intake vacuum leak there, and several exhaust ports leaked. More careful investigation of the alignment of the intake and exhaust flanges during round two led me to decide (thanks to your suggestion) to use two gasket sets in their entirety. Using only two exhaust gaskets on exhaust flanges and one on intakes would I decided create more of a difference than one all around. I did flat file the exhaust manifold flanges, which were not dead parallel to the intakes even after filing. It has been working fine. There is clearly more gasket compression around the intake flanges than around the exhaust flanges.

Dave

If there are no leaks at the heater box, why take the two manifolds apart. I have always left GMC manifolds together and put them on a belt sander to true the surface. Most of them have some warpage.

Good point. As a carpenter, a belt sander sounds good. I think it makes machinists cringe, except as mentioned above, my machinist felt that the rusty exhaust manifolds might chip badly and be ruined if put on his truing machine. (not his word for the machine)