leak at air injector fitting

[Ronald D.]

I am trying to see the best way to seal two of my exhaust air injector fitting where they enter the exhaust manifold, the tubes are new and the threaded holes in the manifolds are a little worn so I am thinking to put a dab of high temp silicone on the threads then snug the tube fitting down, I can get them lightly snug but that won't seal it off, any ideas?

[Joe L.]

Re: leak at air injector fitting

I am trying to see the best way to seal two of my exhaust air injector fitting where they enter the exhaust manifold, the tubes are new and the threaded holes in the manifolds are a little worn so I am thinking to put a dab of high temp silicone on the threads then snug the tube fitting down, I can get them lightly snug but that won't seal it off, any ideas?

Ronald------


I don't think that high temperature silicone is going to work in this application. If the threads are too worn/damaged to allow the tubing nut to hold the tube against the seat in the manifold, you've got a problem. The only way I can think of to repair this is to install Helicoil or other thread repair. The problem is I don't know if they are available in this thread size.

[Steve G.]

Re: leak at air injector fitting

I'm reasonably sure there should be short tubes with a flared end that are slid into the hole first. The nut then tighten the AIR tube down against the flair on the short tube. If your tubes are missing or damaged they won't seal.

Steve

[Joe L.]

Re: leak at air injector fitting

I'm reasonably sure there should be short tubes with a flared end that are slid into the hole first. The nut then tighten the AIR tube down against the flair on the short tube. If your tubes are missing or damaged they won't seal.

Steve

Steve------


Yes, there are inner tubes (they're called EXTENSIONS) and they must be in place. The flange on the extensions forms the seat that the flange on the outer tube seats against.

[Steve G.]

Re: leak at air injector fitting

Yes, that's what I think I was trying to say. The AIR tube seats against the extension, which seats against the manifold. The AIR tube doesn't seat directly against the manifold.

[Joe L.]

Re: leak at air injector fitting

Yes, that's what I think I was trying to say. The AIR tube seats against the extension, which seats against the manifold. The AIR tube doesn't seat directly against the manifold.

Steve------


Yes, I should have been clearer in my original post. The flange on the EXTENSIONS seats against a seat in the manifold. The flange on the outer tube then seats against the flange on the EXTENSION.

The EXTENSIONS and the outer tubes don't actually have a flare. It's more of a flange with a flat face which is formed somewhat like a flare. However, I don't think it can be created using any common flaring tool.

[Steve G.]

Re: leak at air injector fitting

Just for a little additional clarity, if the nut is tightening, there's nothing a heli coil will fix. What happens is the nut bottoms in the manifold threads and the AIR tube is still loose if the extension is not there for the tube to tighten against.

I'm fairly certain he will find the tubes are missing. Back in the day when we removed these things we threaded a tap into the extensions and pulled them out. If he is installing a system back into one that had previously been removed (as opposed to a replacement of an existing) there's a good chance they are gone. Use a length of stiff wire with a small 90 degree bend on the end to stick in the hole and "feel" for the inside opening. It should be about 2" into the hole and not just the other side of the casting.

I'm pretty sure you can make them with a double lap flare. May have to grind the outside circumference of the flare for it to fit easily in the hole. It's a long time ago, but I do recall having repaired or made one. I thought it was a typical flare, but even if it's not the AIR pipe will conform to the flare and will not leak.

[Joe L.]

Re: leak at air injector fitting

Just for a little additional clarity, if the nut is tightening, there's nothing a heli coil will fix. What happens is the nut bottoms in the manifold threads and the AIR tube is still loose if the extension is not there for the tube to tighten against.

I'm fairly certain he will find the tubes are missing. Back in the day when we removed these things we threaded a tap into the extensions and pulled them out. If he is installing a system back into one that had previously been removed (as opposed to a replacement of an existing) there's a good chance they are gone. Use a length of stiff wire with a small 90 degree bend on the end to stick in the hole and "feel" for the inside opening. It should be about 2" into the hole and not just the other side of the casting.

I'm pretty sure you can make them with a double lap flare. May have to grind the outside circumference of the flare for it to fit easily in the hole. It's a long time ago, but I do recall having repaired or made one. I thought it was a typical flare, but even if it's not the AIR pipe will conform to the flare and will not leak.

Steve------


These inner tubes are available in reproduction. The tubes are made from a special, high-nickel stainless steel alloy. They need to be in order to withstand the heat.

By the way, I'm surprised you were able to remove the tubes the way you described. The cars must have been near-new when you did it. Usually, extremely hard, "ceramic-like" combustion products build up on the inner end of the tubes making it difficult to remove them even if you have the manifold off the engine.

[Steve G.]

Re: leak at air injector fitting

Yes Joe, "back in the day" was a very long time ago. I'm older than I look. Removing these things on new and fairly new cars was a pretty common thing back then.

Certainly if they are available in the aftermarket that's the way to go, stainless or not. Reg steel tubing has been passed through exhaust manifolds for chokes forever. Of course eventually they did corrode through, but it took a very long time. The consequence of these tubes burning off over 20 years of continuous use is much smaller than a choke tube burning through, like almost 0. The purpose of the extensions was to get the air into the centre of the exhaust flow where it would be most effective. Given their actual effectiveness in reducing emissions it would probably be undetectable to the tailpipe sniffer if all you did was make up a "seat" to replace the flared end of the extension.

I remember hearing the wife's tale, again back in the day", that when removing the AIR system if you didn't remove the tubes they would heat and sag. Some claimed that somehow they would make it into the valve arena. That they needed the air moving through them to keep them cool. Seeing them still in manifolds decades after the pumps had been removed disproved that claim.

Boy, we're bringing back all kinds of memories.

[Ronald D.]

Re: leak at air injector fitting

OK as always you guys answered my question, the manifolds are on the work bench, they do not have any extension tubes, this car before I bought it had the air pump and tubes removed, I have all the parts but no tubes, there sold now so that should solve the issue, a big thanks Ron

[Joe L.]

Re: leak at air injector fitting

Yes Joe, "back in the day" was a very long time ago. I'm older than I look. Removing these things on new and fairly new cars was a pretty common thing back then.

Certainly if they are available in the aftermarket that's the way to go, stainless or not. Reg steel tubing has been passed through exhaust manifolds for chokes forever. Of course eventually they did corrode through, but it took a very long time. The consequence of these tubes burning off over 20 years of continuous use is much smaller than a choke tube burning through, like almost 0. The purpose of the extensions was to get the air into the centre of the exhaust flow where it would be most effective. Given their actual effectiveness in reducing emissions it would probably be undetectable to the tailpipe sniffer if all you did was make up a "seat" to replace the flared end of the extension.

I remember hearing the wife's tale, again back in the day", that when removing the AIR system if you didn't remove the tubes they would heat and sag. Some claimed that somehow they would make it into the valve arena. That they needed the air moving through them to keep them cool. Seeing them still in manifolds decades after the pumps had been removed disproved that claim.

Boy, we're bringing back all kinds of memories.

Steve-----


When I removed the manifolds from my original owner 1969 350 at about 100,000 miles, most of the tubes had been completely eroded away. The stub that was left was heavily encrusted with combustion by-products.

The reproduction tubes are, as far as I know, manufactured from the same type of material as originals. In fact, I expect that's what makes these things as expensive as they are.

Attached are pictures of an NOS GM tube. You can see the configuration of the flange. Note that it is flat and relatively wide compared to a flare. This flat surface forms the seat that the outer tube seals against.

By the way, the tube pictured is a GM #12338013. This tube is applicable to some 1979 Corvettes. Originally GM #14000363, it was replaced by the GM #12338013 in August, 1990. The seat end of the tube is identical to earlier tubes. However, note the unusual configuration of the forward end. I don't know what the purpose was for this unusual configuration whereas the original 67-78 tubes had square-cut ends. The good news is these tubes could be used for earlier models with or without the ends cut off and they are made of the same high-nickel material. The advantage? They cost WAY less than the earlier tubes which, at the time they were discontinued, cost nearly FOUR times as much from GM. The bad news is that the 12338013 are now discontinued without supercession.

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[John H.]

Re: leak at air injector fitting

OK as always you guys answered my question, the manifolds are on the work bench, they do not have any extension tubes, this car before I bought it had the air pump and tubes removed, I have all the parts but no tubes, there sold now so that should solve the issue, a big thanks Ron

Ronald -

Over the years I've removed the EXTENSIONS from dozens of cars as part of disabling the A.I.R. system, and if you replace each EXTENSION with a #10 x 1/2" flat head stainless steel machine screw, the tube nuts on the air manifolds will seat at exactly the same depth as if the EXTENSIONS were still in place, as the tapered shape under the screw head fills the same area as the flare on the EXTENSION, and the joint is sealed.

[Steve G.]

Re: leak at air injector fitting

Trouble with doing that is that if you are going to leave the innards in the pump you are dead heading the flow. Kind of a waste of energy. Better to let it free flow into the exhaust.

[Joe L.]

Re: leak at air injector fitting

Trouble with doing that is that if you are going to leave the innards in the pump you are dead heading the flow. Kind of a waste of energy. Better to let it free flow into the exhaust.

Steve------


Usually, the pump vanes are gutted before the screw that John describes is installed. It's part of completely disabling the AIR system but keeping the system components in place for originality.

[John H.]

Re: leak at air injector fitting

Trouble with doing that is that if you are going to leave the innards in the pump you are dead heading the flow. Kind of a waste of energy. Better to let it free flow into the exhaust.

Steve -

As Joe noted, this operation also includes gutting the pump so it only serves as an idler pulley, eliminating the most common pump failure mode (shattered vanes/seized pump/shredded belt).