Smog hole in the manifold needs repair 1968
05-01-2019, 06:21 PM
#21
Melting Slicks
I guess I'm missing something here;
When I did mine back in the dawn of time....I realized immediately that the holes were NPT (national pipe tap)
So unless I'm being obtuse....re tap for the nearest NPT and use a stainless steel NPT PLUG.
If you need to there is METRIC NPT's (so to speak) Tapered pipe taps metric...they basically correspond to 'half sizes'.
Because NPT's are tapered...CARE should be used to JUST screw them in low enough to seal....don't want to split that beautiful Ram's Horn!
Unkahal
When I did mine back in the dawn of time....I realized immediately that the holes were NPT (national pipe tap)
So unless I'm being obtuse....re tap for the nearest NPT and use a stainless steel NPT PLUG.
If you need to there is METRIC NPT's (so to speak) Tapered pipe taps metric...they basically correspond to 'half sizes'.
Because NPT's are tapered...CARE should be used to JUST screw them in low enough to seal....don't want to split that beautiful Ram's Horn!
Unkahal
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cor66vette (05-01-2019)
05-01-2019, 08:28 PM
#23
Safety Car
On my 69 the exhaust manifold AIR holes have an inside lip and the tubes seal up against them similar to a brake or fuel line. With the inside lip or seal surface gone, it's going to leak. I would look for another manifold as trying to fix that isn't going to be cost effective.
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cor66vette (05-01-2019)
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cor66vette (05-01-2019)
05-01-2019, 09:08 PM
#25
Le Mans Master
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On my 69 the exhaust manifold AIR holes have an inside lip and the tubes seal up against them similar to a brake or fuel line. With the inside lip or seal surface gone, it's going to leak. I would look for another manifold as trying to fix that isn't going to be cost effective.
Thank you, and being I did not know what the thread size is, I sought out expert advice, one of whom is Bill Hodell, whose name we doubtless recognize as someone who might know a thing or two about these smog systems. He says 1/2 x 18.
05-02-2019, 08:01 AM
#26
Burning Brakes
Yes, thanks. I am leaning in that direction, but I'm still looking to see if these can be saved, but without that inside lip, salvation is uncertain. And I have my eyes out for replacement manifolds in the meantime.
Thank you, and being I did not know what the thread size is, I sought out expert advice, one of whom is Bill Hodell, whose name we doubtless recognize as someone who might know a thing or two about these smog systems. He says 1/2 x 18.
Thank you, and being I did not know what the thread size is, I sought out expert advice, one of whom is Bill Hodell, whose name we doubtless recognize as someone who might know a thing or two about these smog systems. He says 1/2 x 18.
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cor66vette (05-02-2019)
05-02-2019, 10:35 AM
#27
Safety Car
Also, don't forget about the stainless AIR extension tubes that slide into the manifold and provide a seal with the external "tree".
https://www.corvettecentral.com/c3-6...es%26count%3d9
https://www.corvettecentral.com/c3-6...es%26count%3d9
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cor66vette (05-02-2019)
05-02-2019, 11:39 AM
#28
Burning Brakes
@toylman - I just ran a 1/2 x 20 tap- gently by hand - and yes, it seems to thread okay into the manifold (female). I never tried this tap size before, because in my limited experience with this sort of thing, the thread size of the male part is usually the same as the thread size of the female part, and as stated earlier in this thread, the expert advice I sought stated tube thread size (male) to be 1/2 x 18.
Anyway ... once I have a set of tubes, I can check this out further. Thank you.
*EDIT* Luckily I didn't thread too much into the manifold with the 1/2 x 20 tap. The 1/2 x 18 plugs that the previous owner used to plug the holes do not thread in. So should I assume that the tubes would not thread in, either?
Anyway ... once I have a set of tubes, I can check this out further. Thank you.
*EDIT* Luckily I didn't thread too much into the manifold with the 1/2 x 20 tap. The 1/2 x 18 plugs that the previous owner used to plug the holes do not thread in. So should I assume that the tubes would not thread in, either?
I have a friend at my gym who is a retired machinist; I'm going to run this "guess" past him.
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cor66vette (05-02-2019)
Please keep me posted.
05-09-2019, 02:31 PM
#30
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Kind of a follow-up to my story. 
I brought the manifolds to two machinists, hoping they would know of a fix for the A.I.R. holes.
After spending a little time checking them out, each agreed I would be spinning my wheels looking to save them.
Since they are date correct for the car, my plan at this point is to shelf them and include them with the car when I sell it. Also, to locate a replacement pair.
With that said, I'm now looking for a set. If you have please let me know.
https://www.corvetteforum.com/forums...3872765-a.html
Thanks to all who offered input
I brought the manifolds to two machinists, hoping they would know of a fix for the A.I.R. holes.
After spending a little time checking them out, each agreed I would be spinning my wheels looking to save them.
Since they are date correct for the car, my plan at this point is to shelf them and include them with the car when I sell it. Also, to locate a replacement pair.
With that said, I'm now looking for a set. If you have please let me know.
https://www.corvetteforum.com/forums...3872765-a.html
Thanks to all who offered input
Last edited by cor66vette; 05-09-2019 at 03:03 PM. Reason: Added link to WTB thread
06-15-2019, 02:03 PM
#31
Le Mans Master
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I purchased a set and will be selling these manifolds.
Here is the f/s link.
https://www.corvetteforum.com/forums...post1599588201
Thanks again for all the good help.
Here is the f/s link.
https://www.corvetteforum.com/forums...post1599588201
Thanks again for all the good help.
06-16-2019, 01:43 PM
#32
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It looks like you need a step for the tubing flare to seal against. Fixable but I think might be more costly than the value of the manifold. An insert needs to be installed from the other side (cyl head exh port side) to just the right depth. If I did it I would install a threaded plug from the back side - ensuring the correct depth for the tubing flare to seat - and drill a reasonable sized hole in it.
