Exhaust manifold leak / sealing issues

[nmehdikh]

Hi guys, I've been battle exhaust manifold leaks since I've had the car. I can't drive with the windows down or else I get a immediate headache from the fumes. The head has been rebuilt and head side is definitely square/true. If you look at the photos, you'll see I am leaking from a few separate places. I am open to any and all suggestions, so please help.

The intake side is custom ITBs that don't seem to be leaking anywhere. The exhaust is a header set from "Top end performance". The flange on the intake is much thicker than the exhaust, so I have a custom step down washer on the shared bolts, it is unclear how well this is working.

Tomorrow, I will check the exhaust flange for squareness / true. And I will also get more pictures with the gasket (copper) removed, so we can see if there are marks on the head side.

1) Cylinder #1, exhaust leakingout from the top (towards thermostat) and downward/forward.
2) Cylinder #2, exhaust leaking straight up
3) Cylinder #3 and #4 leaking straight downwards.
4) Cylinder #5, leaking towards both sides
6) Cylinder #6, leaking in all directions.

My gut is telling me the exhaust isn't square/true. I don't think this is from not getting the bolts tight enough, their torque spec is so low. Looking at most of the leak paths, and how this exhaust bolts to the head, it doesn't seem like tightening bolts would really help any of these issues.

My plan of attack :
1) Check the exhaust manifold for squareness, and machine flat.
2) Check intake manifold for squareness, machine flat, and thin out sections (to match exhaust manifold thickness) that share stud with the ehxuast
3) Replace studs with allen head bolts and lock washers to make wrench access easier. A couple of the studs are very difficult to get tightened. I am aware studs are less likely to break, but I just can't tighten some of these studs down.
4) Replace gasket? What do you guys recommend? I previously went with the copper because it came highly recommended. Should I be using any sealants?

Photos:
Cylinder #1

Cylinder #2 exhaust

Cylinders #3 through #6


With intake


Cylinder #1 and #2

Cylinder #3 through #5


Cylinder #5 and #6


Exhaust leaks blasting intake manifold



Thanks,

[Dat73z]

Have it all machined so everything is square and true. You can still get the OE graphite gaskets and there are some vendors in Japan that make the graphite gaskets for a variety of bore sizes. I used a thin smear of high temp rtv on mine (oe graphite gasket) just to be sure, but this was also after having everything machined flat. 

[nmehdikh]

I'll have both the intake and exhaust machined flat, but pulling the head to machine it again is quite a large time and money investment.

Is this the oem gasket you are talking about? Do you happen to know the nissan part # so I can try and get it locally?
https://zcardepot.com/products/manifold-gasket-intake-exhaust-oem-280z-280zx?_pos=8&_sid=3cfbea7cf&_ss=r

Is this it? https://www.nissanpartsdeal.com/parts/nissan-gasket-manifold~14035-n3500.html

Edited July 23, 2022 by nmehdikh

[rossman]

The Zcar Depot link looks like the right gasket.  Its a composite graphite gasket.  I've also used Permetex high temp RTV to seal it, where there was pitting around #1. If I were to guess, you either don't have a flat exhaust manifold or there isn't enough clamping force on it. I've never encountered the problem you're having but I would think the flanges should be close to the same height to get enough preload load into both. 

[Dat73z]

The OE gasket you want should also have the metal reinforced sealing area for the header/exhaust side. What you linked from zcardepot looks correct, and it has the injector cutouts for your itbs. 

[Dat73z]

I had to hop way back in my photo archives but I did a skim of high temp rtv on either side of the gasket. It was probably overkill but removing the manifolds on this engine means pulling the engine out of the car. Also not my OE gasket does not have the injector cutouts but you can make out the metal reinforcement areas on the exhaust side.