Intake Manifold bolts

[Tony H.]

What size bolts are on a 1970 LS-5 stock intake (cast iron) manifold? I am curious as to how much 1/16 of a turn will compact a gasket. (ie how many threads per inch??)

Also, are GM gaskets for this application still available? What is the thickness of the intake gaskets?

Thanks.

[Mark L.]

Re: Intake Manifold bolts

Hi Tony,

Intake bolts are 3/8"-16 x 1 1/4". Sorry can't help with the gasket.

[Robert C.]

Re: Intake Manifold bolts

Tony, Paragon sells the correct manifold gaskets.


NCRS-Texas Chapter

[Joe L.]

Re: Intake Manifold bolts

Tony-----

Gaskets for your application are still available from GM under GM #10174981.

[Wayne M.]

Re: Intake Manifold Gaskets

Tony --- Here's the caliper dimensions from an NOS GM # 3860350, an oval port intake gasket from an upper-end rebuild kits # 3917955 and 3957990, circa '69/70. Basic thicknes: 0.048", with an average of 0.070" at the raised ribs surrounding the intake and coolant passages. I don't know what they compress to. These gaskets are a dark gunmetal grey.

[Tony H.]

Re: Intake Manifold bolts

Do you know if the new GM numbers are of the same configuration as the older GM numbers (GM#10174981 vs GM#3860350)?

At the time of my engine rebuild, I was told that GM no longer made the original style intake gasket. The current replacement was thicker and I would have to shave down the original intake to accommodate for the difference in gasket thickness. I recall the rebuilder using an aftermarket gasket which he cut to more closely resemble the original gasket which is visible once the intake is installed.

I am looking into the cause of my high oil consumption, about 1 qt ever 300 miles (4.5 hour of continuous highway miles with a few light/gas stops). No oil is externally visible. I'll start a thread on that later. My engine rebuilder says it's likely the intake manifold gasket leaking internally.???

[NickD.]

Re: Intake Manifold bolts

One revolution would be 1/16" (16 thds/inch) so 1/16 of a turn would be .0039, not counting bolt stretch.

[Tony H.]

Re: Intake Manifold Gaskets NEW thicker than NOS

I measured the ones I bought at NAPA yesterday using calipers and the dimensions are 0.0665" and 0.1000" for the gasket and opening edges, respectively. This confirms, somewhat, what my rebuilder was telling me at the time of my engine rebuild. Will I still be able to use this new gasket without milling the intake? Maybe the additional thickness of the new gasket will resolve the problem of misting oil past the gasket.

[Tony H.]

Re: Intake Manifold Gaskets NEW thicker than NOS

Oh, forgot to ask:

What sealing compound should I use around the water openings when I replace the intake manifold gaskets? Also, should I drain the radiator first when I do this replacement or is there a trick to getting away without draining the radiator and still not getting coolant into the engine when the intake comes off? Would you recommend an oil change after the intake gasket is replaced?