tapping smog exh manifold AIR holes

[Kenneth G.]

hello all,

I have a pair of exhaust manifolds for my 69 350 that had the AIR holes shut with copper(?) fittings. Needless to say the threads of the AIR holes where the AIR manifolds go in are all cruddy. I would like to tap these threads but was unsure as to what size the threads are . Could anyone advise what size they are and what tap to use? also when i thread the AIR manifold in how tight should it go into the manifold (in other words should the air tubes thatgo into the manifold be able to move a bit or should they be "flush"up against the nifold and not move?) thanks

kenny

[Chuck G.]

Re: tapping smog exh manifold AIR holes

Hello Kenny; If you search the recent archives, I asked the same question about a month ago. My 69 big block manifolds were tapped with 1/2 x 18 threads. This is a pipe or tubing thread. Check yours with a pitch gauge to be sure. I ended up CAREFULLY using a 1/4 x 18 pipe tap just to clean my threads. This is a tapered tap and will expand the hole if you're not careful. I was told you can buy a 1/2 x 18 tap from some industrial supply houses, but I didn't go this route. I was also told that this thread, technically is known as a 3/8 tubing thread. Confusing ?? Yes ?? Be very careful and check the archives. When I put the "trees" back on, I snugged them down so that they would hold the pipes, which extend through the manifold holes. I did this off the car, so I was sure that they were right. E Mail me, as I saved/printed all of the responses I received. Chuck Gongloff