Bolt Size To Plug Exhaust Air Tube

[hf240z]

I am removing the air pump, and air tube on my 72 z exhaust manifold. does any body know the exact size and thread to plug the air tube hole on the exhaust manifold.

thanks,

hf

[Bambikiller240]

I've seen it posted on the IZCC list, but don't remember the exact size, however it was said to be a British Standard Pipe (BSP)thread. If anyone knows exactly what we need for this, please post for all of us!

Thanks

Carl

[Royce]

Sorry, don't know the size of the bolt. What a local Z friend did that seems to work well is take the exhaust manifold to a welder and have them cut off the metal tubes on inside and out. Then weld it closed! They said it was better/stronger to weld the metal sleve, what is left of the bolt/tube deal, than to weld to the cast material of the exhaust manifold. They were also concerned that removing the metal threads from the manifold would damage it! Has anyone had luck removing these?

I believe it cost him about $30 at a local welding shop. I may try this if I ever remove all the smog stuff. In fact since I have a few extra manifolds laying around I'll probably prep one just in case! Or should I say, when my air pump stops working!

Hope it helps!

[Bambikiller240]

Originally posted by Royce

(major Snip by Carl) They were also concerned that removing the metal threads from the manifold would damage it! Has anyone had luck removing these?

Hi There Royce:

How are you doing?

I've removed the Air Injection tubes from two manifolds in recent times. While it would not be fair to say that I had no problems doing so, I have not damaged either manifold while doing so.

A good dose of Sili-Kroil penetrant http://www.kanolaboratories.com/ (I soaked cotton balls with it and left them resting on top of each fitting overnight)and a Flare-nut wrench (14mm AIR) was all that was needed for about half of the tubes. The other 6 tubes required the help of a propane torch to heat things up a bit.

Take care!

[HS30-H]

Originally posted by BambiKiller240

I've seen it posted on the IZCC list, but don't remember the exact size, however it was said to be a British Standard Pipe (BSP)thread. If anyone knows exactly what we need for this, please post for all of us!

Ah, BSP threads!

Where would we be without BSP threads? ( up to our knees in water, probably ). BSP is also sometimes described as "British Straight Pipe"...........

The BSP thread system is a tapered design, mainly used in sealing water and gas lines.

In the USA, you will find that NTP ( National Tapered Pipe ) threads are very close to their equivalent BSP sizes. Simply running the appropriate NTP tap down through the BSP hole will enable you to use an NTP pipe plug in there.

I think you will find that both EARL'S and AEROQUIP make BSP fittings ( and presumably plugs ). If not, re-tap to the equivalent NTP size and use an NTP plug.

Good luck,

Alan T.

[Royce]

I am curious about this since I will probably one day do this out of necessity!

If you remove the air tubes but unthreading them what are you left with? Is there a female threaded metal sleve or is it female threads in the cast manifold. If it is the latter would it be possible/advisable to tap the new threads into the cast manifold?

Also, I would think that the type of metal of the plug would be important as to its expansion characteristics so that it wouldn't leak or damage the exhaust manifold???

Hope that last one made sense!

Thanks!!!

[Bambikiller240]

Originally posted by Royce

I am curious about this since I will probably one day do this out of necessity!

If you remove the air tubes but unthreading them what are you left with? Is there a female threaded metal sleve or is it female threads in the cast manifold. If it is the latter would it be possible/advisable to tap the new threads into the cast manifold?

Also, I would think that the type of metal of the plug would be important as to its expansion characteristics so that it wouldn't leak or damage the exhaust manifold???

Hope that last one made sense!Thanks!!!

Hi Royce:

The Air Injection Galley (that air tube manifold with the threaded fittings mounted to the outside of the exhaust manifold) holds the actual (separate) Air Injection tubes in place (inside the Exhaust manifold). The tubes themselves stick out into the exhaust gas stream from there into the cylinder head. They are held in place by the fact that they are flared at their top end, and cannot "fall through" the diameter of the hole they rest in. The bottom end of the fitting that you see threaded into the Exhaust Manifold is tapered (male taper if you will) to match the taper(female taper) of the Air Injection tubes to make a gas tight seal.

It is female threads in the cast manifold, and male threads on the fitting of the Air Injection Galley. The tubes themselves have no threads at all, only a flare at the top.

Hope I haven't confused the issue with my description.

Regarding your mention of the type of material for a plug being important, I agree; however since almost all of the BSP fittings I've seen are found in the Plumbing section of Hardware stores and are made of cast iron (just like the Exhaust Manifold) I don't believe it will be difficult to find fittings of appropriate material once the size is determined.

[kmack]

I used 3/8" NTP flush pipe plugs in my manifold. But then again I also sawed off the injection tubes and then proceeded to drill out the threaded pieces in the manifold. They were too rusted in place to even try to unscrew them. Total process took less than an 2 hours (using a hacksaw, 3/8" portable drill, and a NTP thread tap).

Ran it on the car for a few months and never noticed any leaks.

[2ManyZs]

Uh, sorry, but it's N-P-T for National Pipe Thread.......

[kmack]

Oooh! So just because you have over 2000 posts, you think you're a know-it-all, huh?

[HS30-H]

NTP = "National Tapered Pipe"

NPT = "National Pipe-Tapered"

Now commonly referred to as "NPTF" threads.

Most pipe threads including JIC & Metric are defined by the outer diameter of the male thread. However, BSP and NPTF are defined by the bore of the hose that they fit ( hence a 1/2" BSP fitting fits a 1/2" hose ). Measure NPTF threads at their mid-point

BSP and JIC fittings seal on a coned seating if in a port with a washer or seal, but NPTF fittings seal by slight deformation of the thread. Hence a satisfactory joint can be made between NPTF male and BSP ports.

Just block the BSP-tapped ports with the appropriate NPTF plugs.

Alan T.