Slant 6 exhaust leak.

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dodgemahal

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After much thrashing I finally got my 73 Dart engine running decent. I have very loud exhaust leaks at cylinders 1 and 6. Quiets down after everything gets up to operating temp. Besides replacing the gasket do I get the manifolds decked at a machine shop? Could it be the head is not flat? I suppose once I have it apart I might find another reason for the leak. Any advice? I'm a slant 6 neophyte. Thanks.
 
Possible the manifold is warped. Not likely of a problem with the head. Make sure you have the proper manifold hardware, and it is installed correctly
 
It is very much worth your while to get the good gaskets for the manifolds-to-head and intake-to-exhaust junctions.

Also, if you are still running the original exhaust manifold, be aware that the '70-'72 manifolds make extra hassles. Specifically, they have an open "stove" (hole directly into the inside of the manifold) at the top of the № 5 runner. This is sealed (kindasorta usually not very well) by a stamped sheetmetal cup that fits into the hole, with a (no longer available) gasket around its perimeter. On top of this cup is bolted the choke thermostat. If you are bound and determined to run this manifold, and there's any kind of a fault with or near the choke—doesn't work quite correctly, rod all tweaked and bent, rusty AF, exhaust leaks, etc—fabricate a blockoff plate and cut a suitable gasket for it, then plop a № 1231 electric choke kit on and be permanently done with choke problems.

But given that this manifold is warped and there's a high likelihood of cracks and/or heat control valve faults as well, unless you have no budget, you're best off installing a carefully chosen new exhaust manifold.

Keep in mind that if you have the present manifold planed to address the warpage, its mount flanges will be thinner, which will mess with (lower) the force with which it is clamped to the head by the nuts and washers, and so future manifold-to-head gasket leaks will be more likely. If you try to end-run this by exceeding the specified torque, future manifold cracks become more likely.
 
slantsixdan said:
It is very much worth your while to get the good gaskets for the manifolds-to-head and intake-to-exhaust junctions.

Also, if you are still running the original exhaust manifold, be aware that the '70-'72 manifolds make extra hassles. Specifically, they have an open "stove" (hole directly into the inside of the manifold) at the top of the № 5 runner. This is sealed (kindasorta usually not very well) by a stamped sheetmetal cup that fits into the hole, with a (no longer available) gasket around its perimeter. On top of this cup is bolted the choke thermostat. If you are bound and determined to run this manifold, and there's any kind of a fault with or near the choke—doesn't work quite correctly, rod all tweaked and bent, rusty AF, exhaust leaks, etc—fabricate a blockoff plate and cut a suitable gasket for it, then plop a № 1231 electric choke kit on and be permanently done with choke problems.

But given that this manifold is warped and there's a high likelihood of cracks and/or heat control valve faults as well, unless you have no budget, you're best off installing a carefully chosen new exhaust manifold.

Keep in mind that if you have the present manifold planed to address the warpage, its mount flanges will be thinner, which will mess with (lower) the force with which it is clamped to the head by the nuts and washers, and so future manifold-to-head gasket leaks will be more likely. If you try to end-run this by exceeding the specified torque, future manifold cracks become more likely.
Click to expand...
Great info. I have a '73 manifold so I'm spared some of the problems addressed in this post. I wonder if 73 had it's own set of problems?
 
No, a '73-up manifold will be fine, as long as it's in good condition. The '70-'72 choke won't work on that exhaust manifold, and the '73-up factory choke system sucks, so pick up one of those № 1231 electric choke kits and off you go.
 
Thanks Dan! I love the info and options. I thought this 73 4-door dart would be an inexpensive resto project, but it's sucking up all my money. I guess it sat too long. I suppose it's never cheap to restore a ride!
 
Manifold outlet is 2" and the headpipe is a pathetic 1-3/4" piece; make a note to get a 2-1/4" headpipe made when the time comes.
 
So if I stay with what I have, do I need to order a 2 or 2.25 inch gasket? I will make a note of that 2.25 head pipe, but for now I want it to run, so I'll be able to pull it in and out of the shop,

slantsixdan said:
Manifold outlet is 2" and the headpipe is a pathetic 1-3/4" piece; make a note to get a 2-1/4" headpipe made when the time comes.
Click to expand...

as I do the body sanding, outdoors.

I'd like to get all the parts and tools gathered and ready before I start disassembly.
 
The flange is the same as either side of the big block. The gaskets I have, have a 2-1/4 hole, same as the B B flanges.
I gasket matched the manifold outlet to the gasket I have.
The manifold flange hole as cast in mine was 1-7/8 diameter to start out with. And well off center. In order for the hole in said gasket to line up with hole in manifold I had to grind heavy on one side, and didn't touch about 1/4 of the hole.
 
That's interesting. I actually have both sizes ordered. I can't wait to see how this all shakes out!
 
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