C3 BB exhaust manifold AIR Tube Assemblies Thread size

[Patrick N.]

I will need to re-tap the threaded holes in the exhaust manifold for fitting the AIR tube assemblies (68 BB). The prior owner filled them in with an epoxy. Does anyone off hand have the thread size? I will need to buy this tap - not in my current set of tools.

Thanks again,
Pat

[Terry M.]

Re: C3 BB exhaust manifold AIR Tube Assemblies Thread size

I will need to re-tap the threaded holes in the exhaust manifold for fitting the AIR tube assemblies (68 BB). The prior owner filled them in with an epoxy. Does anyone off hand have the thread size? I will need to buy this tap - not in my current set of tools.

Thanks again,
Pat

Pat,

Two of the five "similar threads" shown when you scroll down on this page will answer your question.

[Dick W.]

Re: C3 BB exhaust manifold AIR Tube Assemblies Thread size

Patrick, to clean the threads you will need a bottoming or plug tap. Conventional taps have a tapered starting area and will leave the bottom threads in you manifold untouched. As the other threads state it is 1/2"X20 thread.

[Terry M.]

Re: C3 BB exhaust manifold AIR Tube Assemblies Thread size

Patrick, to clean the threads you will need a bottoming or plug tap. Conventional taps have a tapered starting area and will leave the bottom threads in you manifold untouched. As the other threads state it is 1/2"X20 thread.

1/2-20 NPS = National Pipe Straight. That last part is kind of important.

[Dick W.]

Re: C3 BB exhaust manifold AIR Tube Assemblies Thread size

1/2-20 NPS = National Pipe Straight. That last part is kind of important.

Only NPS in 1/2" is 14 tpi. 1/2"X20 conventional tap will work fine.

[Patrick N.]

Re: C3 BB exhaust manifold AIR Tube Assemblies Thread size

Thanks guys, I will get the recommended taps.
I plan to carefully drill out most of what appears to be epoxy material then re-tap. Have you ever found a wounder chemical that removes or can soften epoxy?

Best,
Pat

[Clem Z.]

Re: C3 BB exhaust manifold AIR Tube Assemblies Thread size

Thanks guys, I will get the recommended taps.
I plan to carefully drill out most of what appears to be epoxy material then re-tap. Have you ever found a wounder chemical that removes or can soften epoxy?

Best,
Pat

MEK Methyl ethyl ketone

[John H.]

Re: C3 BB exhaust manifold AIR Tube Assemblies Thread size

Actually, the threads in the exhaust manifold holes for the air manifold tube nuts are 1/4"-18 N.P.S.F. (straight pipe thread).

[Patrick N.]

Re: C3 BB exhaust manifold AIR Tube Assemblies Thread size

Just want to say thanks guys! Threads are clean and the tubes went on without issue. Next up is a call to Bill Hodel to complete the system.

Best,
Pat

[Joe L.]

Re: C3 BB exhaust manifold AIR Tube Assemblies Thread size

Just want to say thanks guys! Threads are clean and the tubes went on without issue. Next up is a call to Bill Hodel to complete the system.

Best,
Pat

Pat-----


Much of the system is available in reproduction. The pump can be purchased pretty easily in the automotive rebuilt parts marketplace (although Bill Hodel's rebuilds will be more exactly correct and better finished). The "stickler" will be the diverter valve. That's the BIG $$$$$ piece, from Bill or anyone else.

[Patrick N.]

Re: C3 BB exhaust manifold AIR Tube Assemblies Thread size

Pat-----


Much of the system is available in reproduction. The pump can be purchased pretty easily in the automotive rebuilt parts marketplace (although Bill Hodel's rebuilds will be more exactly correct and better finished). The "stickler" will be the diverter valve. That's the BIG $$$$$ piece, from Bill or anyone else.

Wow- you weren't kidding. 28296- That is a lot of coin for such a small part. I spoke to Bill Hodel-like everyone said- super nice guy to talk to and very knowledgeable!!

Joe, would have any info on what application a pump manufactured in very late 67 (Dec 12th) without a pressure relief valve was used for in 68? passenger car-truck-service? I have this pump with my car currently but think it may no be correct. Date code is 346 7 1Z? I have researched that some 68 pumps with the "1Z" code did not have the relief valve but it does not explain what vehicle it was intended for.

Thanks,
Pat

[Joe L.]

Re: C3 BB exhaust manifold AIR Tube Assemblies Thread size

Wow- you weren't kidding. 28296- That is a lot of coin for such a small part. I spoke to Bill Hodel-like everyone said- super nice guy to talk to and very knowledgeable!!

Joe, would have any info on what application a pump manufactured in very late 67 (Dec 12th) without a pressure relief valve was used for in 68? passenger car-truck-service? I have this pump with my car currently but think it may no be correct. Date code is 346 7 1Z? I have researched that some 68 pumps with the "1Z" code did not have the relief valve but it does not explain what vehicle it was intended for.

Thanks,
Pat

Pat------


I do not know of ANY 1968 applications that used an AIR pump without a pressure relief valve. A pump dated as you describe would seem to imply that there was such an application but I don't know of it and can't even imagine what it would be. Why? Well, as far as I know, no 1968 diverter valves included a pressure relief function. So, the pump had to have a pressure relief valve. For 1969, things changed. Most 1969 diverter valves include a pressure relief function. So, these applications do not require a pump with the valve (although a pump with the valve can be used for 1969+ applications).