1969 427/400 Air Tube Assembly

[Ned T.]

Should the A.I.R. Tube assembly touch against the A.I.R. Tube extensions when installed? I ran a 1/4" NPT tap into the manifold threads but I can't seem to get the tube assembly to go all the way in against the tube extensions. My threads in the manifold aren't the best and seem to be missing a few threads down inside, which I thought would allow the assemble to thread in further. If they don't come in contact with the extensions won't they rattle around in there?

[Ralph S.]

Re: 1969 427/400 Air Tube Assembly

you need to use a bottoming tap. not a tapered one.

[Ned T.]

Re: 1969 427/400 Air Tube Assembly

Ralph,

I did looked for a bottoming tap, and the industrial supply store never heard of it. Then I looked in Grainger's catalog and they don't describe it as a "bottoming tap", but they do have a "plug tap" so I'm thinking that's the one. However, I can see how a bolt thread can use a bottoming because the threads are straight and the tap can have the same diameter from top to bottom. The NPT tap would also have to have the taperd threads to the correct lenght that a standard 1/4" pipe thread threads in to tap all threads at the same time. I will check with a Steamfitter I know today to see what he has.

[John H.]

Re: 1969 427/400 Air Tube Assembly

Ralph,

I did looked for a bottoming tap, and the industrial supply store never heard of it. Then I looked in Grainger's catalog and they don't describe it as a "bottoming tap", but they do have a "plug tap" so I'm thinking that's the one. However, I can see how a bolt thread can use a bottoming because the threads are straight and the tap can have the same diameter from top to bottom. The NPT tap would also have to have the taperd threads to the correct lenght that a standard 1/4" pipe thread threads in to tap all threads at the same time. I will check with a Steamfitter I know today to see what he has.

Ned -

The threads in the exhaust manifold holes for the air manifold tube nuts are 1/4"-18 (NPSF) National Straight Pipe Threads, not the more conventional tapered (NPT) pipe threads.

[Ned T.]

Re: 1969 427/400 Air Tube Assembly

John,

Now I understand. I'm in the construction business and I'm familiar with the straight pipe thread. This is used on all electrical conduit pipe threads, where as the fluid pipes use the tapered threads.

Thanks for the information.

Ned