I have removed the seized exhaust studs and broken EGR tube fitting on the exhaust manifold with a lot of patience and heat cycles with the oxy/acetylene torch.  I will not be using the EGR valve and would like to thread a sealing plug into the manifold.  The thread size on the fitting does not look like a common thread size.  Any suggestions before sending the manifold to get bead blasted and then I will be priming and painting it with the VHT exhaust paint.  EGR block off plates are easy to find but have not been able to locate any info on that tube thread size.  Thanks in advance for any help.  Resurrection project slowly progressing between work, family, and church .  Thanks again, John-Lugoff, SC.

I actually have a manifold from a 77' on my bench but I haven't been successful as to removing the egr tube from it.  I do know the nut is 24mm, or should I say was……  It's really on there.

Edited February 23, 20178 yr by gwri8

It definitely took several heating and cooling cycles with the oxy/acetylene torch for the EGR tube.  Once it got started it came out quite nicely.  A 2ft breaker bar and 6 point socket got it broke free and after that just a 1/2 drive ratchet.  Still looking to get a thread size so I can plug it off neatly.  I dropped off the manifold today to get it bead blasted and will be priming and painting it with the VHT products next week when I get a bit of time.  Suggestions on the plug size and best material-steel, brass ? will be much appreciated.  Thanks, John-Lugoff, SC.

Your talking about the plug on the exhaust manifold correct? Did you see this:

https://zcardepot.com/engine/exhaust/oxygen-sensor-and-egr-exhaust-plug-7-8.html?search=Egr

Thanks so much!  That is exactly what we need to finish off the exhaust manifold.  I will be ordering that plug and new studs later tonight.  Thanks, John-Lugoff, SC.

Very pleased with the work at a local automotive machine shop-Rabons-Lugoff, SC.  He removed the snapped off stud I was unable to remove from the cylinder head-rear exhaust-and installed the Heli-Coil insert.  Looks very good and also had them bead blast the exhaust manifold.  I am also very pleased with the VHT primer and paint I sprayed the exhaust with.  No runs, no drips, no errors. Not my usual outcome with spray cans.  Looks great and will be installing the new studs and EGR tube block plug in a few days after the paint cures.  Will also be using the high temp never seize on all those threads.  Now if only the rest of the project looked as nice as the exhaust manifold.  Rabons will also be doing the rest of the needed machine work on the bottom end when I pull out the engine.  Quality work at fair prices. Looking forward to resurrecting one piece at a time as time and money allow.  The exhaust manifold is oddly the first piece completed in this long project.  Thanks for all the help, John-Lugoff, SC.

Going back to the original question.  Thread size on EGR tube in the exhaust manifold on 78 280z.  I purchased the plug but it does not thread into the manifold.  It is advertised as a 7/8" but but a 7/8-14 nut does not thread on.  Using a micrometer shows the plug is a 22mm.  A M22x1.5 nut does not thread on either.  A call to the plug supplier tech department revealed there is a question on the actual thread dimensions.  The original part still threads into the manifold but is in real bad shape and a bit deformed from the intense heat and torque that was needed to remove it.  The end threads in the manifold are a bit damaged from age and was hoping to just run a tap down through to clean up the threads.  I have found M22x1.25 taps but no success finding a nut to verify the thread pitch on the new plug.  I hate to waste the cost of a tap that may still not be the correct one.  The original EGR fitting is certainly tapered at the end and  that makes it easier to thread into the manifold while the new plug has a blunt end that is not starting to thread into the slightly damaged end threads on the manifold.  Any definite verification on the thread size will be greatly appreciated.  Progress on the project is SLOW but very gratifying.  Thanks for all the help-John-Lugoff, SC.

Much of the Z car's plumbing is BSPT, British Standard Pipe Thread.  Very close to NPT but no cigar unless you use brass or copper so the threads can deform.   Probably where your supplier got screwed up.  The taper is different, and the size of the small taper can be also, making them hard to start even if you do plan to mash up the threads.   

http://www.ralstoninst.com/news/story/the-difference-between-npt-bspp-and-bspt-seals

Read up on the oil pressure senders for more examples.  

I ran an M16 bolt in to the remains of an EGR tube, to plug it.  Maybe you could make your own fitting by tapping the inside of the piece you pulled, to whatever thread you want.  Bend your own tube.  Essentially building your own EGR tube.

Edit - McMaster Carr has a selection of BSPT stuff.

Edited March 21, 20177 yr by Zed Head

I am not planning on using the EGR,  I will double check the dimensions of the BSP threads,  It is definitely not tapered but BSP does have a straight thread if my memory serves me correctly.  I may end up using the old fitting and threading the inside of it and install a plug.  Getting the leftover tube out of the fitting may be a project.  Thanks for the suggestions.  Any other definite answers will be greatly appreciated.  Thanks, John-Lugoff, SC

The original fitting measures .842 diameter, the replacement plug sent measures .865 diameter.  Nothing coming up on the BSP chart with close dimensions to those.  I will continue to investigate the situation and may end up trying to get the tube out of the original fitting and then tapping it to thread in a plug as suggested .  Any other input will be greatly appreciated.  22mm is equivalent to .866 so I am assuming the replacement plug is 22mm but the 1.50 thread pitch nut would not mate with the plug threads.  Could it be M22x1.25 thread?  Thanks, John-Lugoff, SC

I turned the original steel hex fitting into a plug by MIG welding the center of the nut section solid, then grinding it smooth.  Worked well for me.

On 2/22/2017 at 5:37 PM, One Way said:

I have removed the seized exhaust studs and broken EGR tube fitting on the exhaust manifold with a lot of patience and heat cycles with the oxy/acetylene torch.  I will not be using the EGR valve and would like to thread a sealing plug into the manifold. 

I missed your objective in my last post.

I felt comfortable plugging mine with a bolt and some muffler sealing ceramic goop because I realized that the fitting does not see much pressure, just high temperature and many heat cycles  I turned my bolt in to a self-thread-cutting bolt by grinding a notch in the threads, and putting a slight taper on the nose.  It turned in with a comforting level of force required.  It was tight when done.  It's been there about 20,000 miles with no signs of leaks or loosening.

 

Edited March 24, 20177 yr by Zed Head
Extra M

Thanks for the replies.  Definitely leaning toward home fabricated plug.  Just very odd there does not seem to be any standard thread to fit, but it is what it is and will do some home brewed engineering.  I guess that is what makes the old car hobby so challenging and enjoyable.  Thanks again. John-Lugoff, SC.