69 exhaust manifolds and AIR system questions and issues

[Don W.]

Hi All,

I bought the AIR system from Bill H and someone installed the wrong thread plugs for the AIR injection tubes on the exhaust manifolds, removed the pipe thread steel bungs/plugs and they are larger thread then the 1/2-18 AIR injection tubes; like pipe threads. So my options are to overdrill and install inserts with the correct size threads or look for correct dated and matching exhaust manifolds. Any suggestions on availability, cost and point impact? My current manifolds are correct dated.

Also, exhaust manifold bolt kit (miss match bolts) so where do I look for correct bolts and does the manifold use heat shields or stainless lock tabs like a lot of other years to be NCRS correct?

69 427/390HP

Thanks,

Don

[Joe L.]

Re: 69 exhaust manifolds and AIR system questions and issues

Hi All,

I bought the AIR system from Bill H and someone installed the wrong thread plugs for the AIR injection tubes on the exhaust manifolds, removed the pipe thread steel bungs/plugs and they are larger thread then the 1/2-18 AIR injection tubes; like pipe threads. So my options are to overdrill and install inserts with the correct size threads or look for correct dated and matching exhaust manifolds. Any suggestions on availability, cost and point impact? My current manifolds are correct dated.

Also, exhaust manifold bolt kit (miss match bolts) so where do I look for correct bolts and does the manifold use heat shields or stainless lock tabs like a lot of other years to be NCRS correct?

69 427/390HP

Thanks,

Don

Don------


I don't know if thread repair inserts are available for the thread size required here. If they are, I think that would be your best plan. If such inserts are available, I would expect that McMaster-Carr would have them. Keep in mind that there is a seat at the base of the threads. This seat is important and you don't want to damage or drill it out as part of the effort to install the inserts.

No heat shields or french locks were used with these bolts for 1969. The end bolts were a special locking thread bolt of GM #3909821 and these were a flanged head type bolt. The remaining bolts were GM #3736035 and were a standard hex head, non-flanged head bolt. The 3909821 is still available from GM although the headmarking will not be the same as original. The 3736035 should be available in reproduction.

By the way, the headmarking on the original bolts was NOT the same for both of the above-referenced. So, "mismatched" is how it was then and, presumably, should be now.

[John H.]

Re: 69 exhaust manifolds and AIR system questions and issues

Hi All,

I bought the AIR system from Bill H and someone installed the wrong thread plugs for the AIR injection tubes on the exhaust manifolds, removed the pipe thread steel bungs/plugs and they are larger thread then the 1/2-18 AIR injection tubes; like pipe threads.

Don -

Those air manifold tube nut threads are 1/4"-18 NPSF (STRAIGHT pipe thread, not tapered).

[Greg L.]

Re: 69 exhaust manifolds and AIR system questions and issues

The thread repair kit is available but it wasn't cheap! I'm thinking it was in around $150.00 CDN and that included 10 inserts. I went for it because they were my original manifolds. Don, if you are interested I can try and find my old kit to get you a kit number. It was a bit of a pain installing them because I had to make a jig so that each manifold would be perfectly perpendicular to the drill press.

[Don W.]

Re: 69 exhaust manifolds and AIR system questions and issues

Hi Greg...I have it in a shop now and we are going to use Helicoils to repair the ones that can't be properly tapped out...Don

[Floyd B.]

Re: 69 exhaust manifolds and AIR system questions and issues

...so where do I look for correct bolts ... to be NCRS correct?

It depends on how exact you want to be. You could get a repro "kit" from any one of the usual suspects but then your manifolds will look like they were put on with a kit (no duh!). You could mix a few kits to get a mixture of head marks that looks somewhat correct but you'll still take deductions on originality. You can get a set of originals from reputable sources like Rich Pasqualone or Rich Fortier but it won't be cheap. It's not that these gentlemen are greedy - not many nice originals survive due to the harsh environment of heat and elements in which these bolts exist. I paid $240 for a full set of originals for the same '69 L36 at Carlisle two years ago.

[Joe L.]

Re: 69 exhaust manifolds and AIR system questions and issues

It depends on how exact you want to be. You could get a repro "kit" from any one of the usual suspects but then your manifolds will look like they were put on with a kit (no duh!). You could mix a few kits to get a mixture of head marks that looks somewhat correct but you'll still take deductions on originality. You can get a set of originals from reputable sources like Rich Pasqualone or Rich Fortier but it won't be cheap. It's not that these gentlemen are greedy - not many nice originals survive due to the harsh environment of heat and elements in which these bolts exist. I paid $240 for a full set of originals for the same '69 L36 at Carlisle two years ago.

Floyd------


If you're talking about used bolts, I don't recommend them for exhaust manifolds. These bolts suffer extreme temperature changes and eventually become extremely hardened to the point of becoming brittle. I recommend only using new bolts, even if they're reproductions.

[Floyd B.]

Re: 69 exhaust manifolds and AIR system questions and issues

Floyd------


If you're talking about used bolts, I don't recommend them for exhaust manifolds. These bolts suffer extreme temperature changes and eventually become extremely hardened to the point of becoming brittle. I recommend only using new bolts, even if they're reproductions.

I think it depends on your goal for the car. If you plan on having it judged and hope to get to 97% then I think you're headed to "trailer queen" territory. For example, I have a full set of original Goodyear Speedways from 69 and 70. Would I ever drive on those tires? of course not. Will I put them on the car for judging? you bet. I have an original set of manifold bolts but I would not install them for long-term driving simply because they cost to much.

BTW, I won't get into a long discussion of metallurgy here but heating a metal to it's critical point will actually relieve stress in the crystal lattice inducing ductility, not harden it. To harden a metal it is usually deformed (e.g. forged, hammered, etc.) to create stress in the crystal structure (molecular alignment). This is why metal objects such as tools, automotive parts, etc. are often cold forged.

[Joe L.]

Re: 69 exhaust manifolds and AIR system questions and issues

I think it depends on your goal for the car. If you plan on having it judged and hope to get to 97% then I think you're headed to "trailer queen" territory. For example, I have a full set of original Goodyear Speedways from 69 and 70. Would I ever drive on those tires? of course not. Will I put them on the car for judging? you bet. I have an original set of manifold bolts but I would not install them for long-term driving simply because they cost to much.

BTW, I won't get into a long discussion of metallurgy here but heating a metal to it's critical point will actually relieve stress in the crystal lattice inducing ductility, not harden it. To harden a metal it is usually deformed (e.g. forged, hammered, etc.) to create stress in the crystal structure (molecular alignment). This is why metal objects such as tools, automotive parts, etc. are often cold forged.

Floyd-----


I've snapped the heads off or otherwise broken long in-service exhaust manifold bolts. That's why I've always assumed that the the metallurgy of the bolts was compromised by heat.

[Floyd B.]

Re: 69 exhaust manifolds and AIR system questions and issues

Joe,

This definitely isn't my area of expertise but I doubt that heat was a direct factor in the failure of the bolts. Heat will contribute to the eventual failure in other ways though. In ferrous metals I would assume heat could hasten the oxidation but even more likely is that the manifolds will expand when heated thus "stretching" the bolts and deforming them ever so slightly with each heat/cool cycle. I'm definitely not arguing with you. I can't remember off the top of my head but aren't the manifold bolts grade 5 or grade 8? Meaning they're already hard/brittle from the start. They then exist in a very harsh environment. This is why very few survive 40 years. So I would take your advice and never use a set of originals for a car that is driven regularly. I put them in the same class as my 45 year old tires.

[Joe L.]

Re: 69 exhaust manifolds and AIR system questions and issues

Joe,

This definitely isn't my area of expertise but I doubt that heat was a direct factor in the failure of the bolts. Heat will contribute to the eventual failure in other ways though. In ferrous metals I would assume heat could hasten the oxidation but even more likely is that the manifolds will expand when heated thus "stretching" the bolts and deforming them ever so slightly with each heat/cool cycle. I'm definitely not arguing with you. I can't remember off the top of my head but aren't the manifold bolts grade 5 or grade 8? Meaning they're already hard/brittle from the start. They then exist in a very harsh environment. This is why very few survive 40 years. So I would take your advice and never use a set of originals for a car that is driven regularly. I put them in the same class as my 45 year old tires.

Floyd------


I believe they are grade 8. However, they do not have a traditional grade 8 headmarking (i.e. 6 radial lines). Instead, they have a "circular" headmarking. I assume this denotes some sort of special properties but I certainly don't know that for sure.

By the way, the long manifold bolt is also used for the Muncie linkage long attaching bolt (i.e. linkage to 63-65 tailhousing or 66-81 bracket). I've had the heads of these break, too, even though they are not subject to any significant heat.

[Floyd B.]

Re: 69 exhaust manifolds and AIR system questions and issues

I guess I'm not surprised. I don't know if you have ever taken the time to look at these bolts when they break but I have noticed the fractured section is unusually "rough" in appearance. They almost look like a fractured piece of granite. I think grade 8 steel is simply defined as "medium carbon alloy steel, quenched and tempered, minimum tensile strength 150,000 psi." This leaves a lot of room for variation. There are any number of materials that could be used as the alloy component including the carbon. Any material included in the steel will interfere (stress) with the molecular structure of iron's crystal lattice and add hardness/strength but other materials are chosen that will also add other properties such as heat strength, work hardenability, corrosion resistance (e.g. stainless), etc.