I am thinking of removing the "smog rail" (right term??) from my stock '71 240Z. It looks like I will have to plug the holes in the manifold with pipe plugs. Anybody know what size/thread plugs I will need?

It looks like all the fittings are pretty rusty/corroded, can I expect them to be so stubborn as to cause problems??

I am planning on swapping this motor next spring, so if this is a tough job, I may just wait until I pull the motor or replace the headers down the road.

Any help???

Regards,

Astrohog

Here's what I did...

Here's a pic of the exhaust air tube plugs I got from McMaster-Carr. They are 1/4" BSPT hex head and I think they look pretty nice.

Use a little high temp thread sealant when you install them.

With that big hex head, I'll be able to remove them if required...

It looks like all the fittings are pretty rusty/corroded, can I expect them to be so stubborn as to cause problems??

In my experience, yes. It can be virtually impossible to get those out if they are badly rusty. On one of my stock manifolds, they had become one with the manifold casting. If you are thinking about swapping to headers later, I'd let it be. Because if you break one off and can't plug it, you'll have a nasty exhaust leak.

But if you do be sure to pull out the 4" tubes that go into your head from under the rail.

Cheers, Mike

I removed mine, however the manifold was off the engine and on my bench. I purchased the correct plugs from the local hardware store. I wll check to find the size and thread for you if you are still interested.

I believe they were either M10x1.25 or M12x1.25. I found some hex head stainless plugs that worked nicely. removing the old tubes with the head attached to the engine would have been nearly impossible. A hammer and punch were required to remove the carbon covered tubes that extend into the exhaust ports.

Standard NPT pipe plugs work well. The hex-head units pictured above would provide more "purchase" than the allen-head plugs I put in, but I like them because they fit in flush.

As for removal, taking the carbs and intake off is best, if not absolutely necessary. At some point you'll really want the exhaust manifold out where you can really work with it. If you are willing to sacrifice the little air injection tubes, you can snip them close to the nuts and have box end wrenches and 6-point sockets at your disposal.

Soak with penetrant oil, and be patient. Soak again, and even be willing to come back another day. A (brake) flare wrench might do the job if you wanted to get the whole thing out intact, but you'll need some luck. I doubt an open end would do it. There's always vice-grips as a last result.