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Discussion Starter · #1 ·
So, my project '84 was all but ready to be certified road worthy.  All I had to do was find a small exhaust leak that would prevent it passing inspection.  Its just a basic safety inspection, but the sound of the exhaust leak would be enough for them to send me packing.  After about an hour I finally figured out it was the damned smog tubes that attach to the back of each exhaust manifold.  Each had sheared its bolt and was flopping around, leaking exhaust.  The tubes also have a break at one of the Y connections near the firewall.  There are no replacement parts.

So, I pull both the manifolds thinking I'll drill/tap them where the bolt sheared to either block them off or to reattach the smog tubes.  Half of the 12 bolts/studs shear off in the head.  So, I pull the heads.  Yeah, it was a fun day.

Now that I have the heads off I'm thinking why not just plug the smog ports in the heads (tap them, screw in a plug)?  This way I can run headers if I choose to (no plans, but maybe someday).  It will also mean that I won't have to worry about doing anything to the exhaust manifolds, since the ports in the head will be sealed.

Am I right about that?  Plug the smog ports in the head and the whole smog/EGR system is rendered moot?  Oh, I guess I'll need to block off the EGR valve at the intake.  Anything else?
 

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If you plug the holes in the ports, tap it to 1/4-20 and install set screws.  Some will swedge brass in there to plug them off.  The ports int he back of the manifold can be tapped to either 3/8 or 1/2 NPT(can't remember which).  Thats how the factory did it on vehicles that didnt' have the smog tubes on the back.  The bolt holes will still have to be covered up too so either leave the sheared off bolt in there or put another bolt in there.  Don't worry about the EGR valve now its not doing anything if there is no vacuum to it.
 

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Discussion Starter · #3 ·
Thanks - that gets me most of the way there.  But, do I *need* to plug the holes in the back of the ex. manifold if the ports on the heads are plugged?  I'm not sure, but I *think* the smog port section of the manifolds is completely separate form the normal flow of exhaust.  At least that's the way it looks... haven't really tested this theory yet.
 

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I"m not sure, I was thinking they need to be plugged or you will have an exhaust leak.
 

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I suggest you check the size of the smog ports before you go out and buy set screws.  A set of 587 heads I did a few years ago did not have enough meat (hole was too big) to tap to 1/4-20 and instead I had to go to 5/16-18. 

Also, the AIR Pump system and the EGR are separate - one doesn't control or affect the funtion of the other.  You could do what I did - plugged the EGR ports down in the floor of the intake manifold plenum basically rendering the EGR system non-functional.  I still had the EGR mounted and all the vacuum lines running to it to look like it worked.  That was until this past week when I stripped the maze of emissions vacuum lines, vacuum switches, and associated gear from the motor - IT WAS LIBERATING!  Cleaned up the engine compartment and the truck will now idle steady at 800 rpm.
 

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Discussion Starter · #7 ·
OK, I spent a while going over those exhaust manifolds.  The ports on the rear are connected ONLY to the small smog ports where it bolts to the head.  There is a separate plenum that connects these - separate from the main plenum for the normal flow of exhaust.  I went so far as to connect a garden hose to the hole in the back to see where the water flowed.

When I think about it that makes sense.  Why have the smog ports on the head - that simply connect to the main exhaust port via small hole - if the exhaust manifold is just going to re-mix the flow from the smog ports with the normal flow of exhaust?

But, there is also a tap in the collector of the passenger side manifold, just above the connection with the tail pipe, that connects to the whole air pump system of pipes.

So, while I don't need to plug the holes at the back of the manifold (because the heads themselves will be plugged), I do need to find a way to plug the one at the bottom of the passenger side manifold.  The threaded fitting is heavily rusted.  Its soaking in PB Blaster now...
 

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I just did mine a couple weeks ago.  84 318 same setup.

I cut off the air injection tubes flush with the outside of the mounting plate.  I left the 1/2" stub that slid into the exhaust manifold attached.

I purchased a steel rod from the local hardware the same size as the inside diameter of the injection tube stud.  I slid it from the inside until it was flush with the outside of the mounting plate.  I then took a standard propane torch with MAPP gas and heated it cherry red and brazed it with a brazing rod I got from the hardware store.  I cut the rod off flush with the end of the 1/2" tube that inserted into the exhaust manifold.  I cleaned it up a bit with the grinder and wire brush.

That left me with a plug to slide into the exhaust manifold with the original mounting plate to bolt it on with.

I purchased an 18" square sheet of exhaust gasket material from NAPA and cut gaskets to fit.

Worked like a charm.

I did the same concept with the threaded fitting down near the heat riser valve.  Cut off the tube, pulled out the "pipe", brazed in a steel rod in it's place, cut it off flush and dressed it up with the grinder.  I threaded it back in.

The truck ran better immediately.  It must have been all the rust holes, maybe bad check valves.  And I can see half the engine...

I did the EGR (not related to the air injection system) this past weekend, I traced a pattern of it's base on a 3/16" steel plate.  I then cut it out with a jig saw, ground the edges and drilled holes.  I used the same gasket material. Looks better than the factory one in my 77'.  It's running better all the time.  And there is an engine under all that stuff :)



 

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Discussion Starter · #9 ·
Good stuff, Copper Top., thanks.  My tube at the heat riser valve is so rusted I may never be able to thread it out of the manifold.  But, I can probably do the brazing you mention to the tube while its still attached, as long as the manifold doesn't absorb too much of the heat.

I plan to do just what you did to the EGR.  I noticed MOPAR Performance is selling a set of block off plates for the EGR and smog ports on the manifold... for $65!  I laughed so hard it woke the kid.  There's maybe a $1.75 worth of materials in that set.
 

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madurobob said:
Good stuff, Copper Top., thanks. My tube at the heat riser valve is so rusted I may never be able to thread it out of the manifold. But, I can probably do the brazing you mention to the tube while its still attached, as long as the manifold doesn't absorb too much of the heat.

I plan to do just what you did to the EGR. I noticed MOPAR Performance is selling a set of block off plates for the EGR and smog ports on the manifold... for $65! I laughed so hard it woke the kid. There's maybe a $1.75 worth of materials in that set.
Yeah, I just found an old 70's Motor, and robbed it of its manifolds (non air pump assisted) and its EGR, block off plate, few bucks at the junkyard well spent. I too wouldnt dare spend 65 bucks on a few small peices that could easily be made out of some common materials found at the local hardware store!
 

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NorCalCowboy said:
Yeah, I just found an old 70's Motor, and robbed it of its manifolds (non air pump assisted) and its EGR, block off plate, few bucks at the junkyard well spent. I too wouldnt dare spend 65 bucks on a few small peices that could easily be made out of some common materials found at the local hardware store!
That's what I wanted. The parts from my 77' look like they would match perfectly. I spent hours looking through yards without luck. Most of the good stuff is long gone.

This way may have been more work; but it's hard to say. When you start taking exhaust components apart, it's easy to get into trouble. The only real expense was the steel and the gasket material. Wow has that stuff become expensive. I still don't have more than 50.00 in the whole project and I have enough leftovers for a lot of other improvements I need to make.
 
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