Club 80-90 Forums

My exhaust manifold gasket keeps burning out in about every 5 years or more often. I have resurfaced the manifold, tried to use different premium brand gaskets but still burns out.
Usually at the the gearbox side last cylinder.
I have the OE thick washers and used new nuts.
(Mtdi with JX manifold and AAZ turbo)
What could cause this? Too high EGT? Too much EMAP?
Next time I will try a multilayer stainless steel gasket but it bothers me why the standard gaskets did not work.

iirc the ports on the engine are slightly bigger than the ports on the manifold
if this is the case do you enlarge the gasket to match the ports on the head or leave the gasket original JX size - or are you using a AAZ or TDi gasket ?
I don't do diesel so may be completely wrong about all this

Thanks!
The exhaust holes are the same on all the different diesel manifolds AFAIK. But there are some size differences between the head and the manifold that is sure - this is why some says porting them together makes some extra power.
I have ised the gaskets as is.

First I have tried the JX style early 4 piece gasket kit a few times. Now I have the one piece later style gasket. They all sealed well in the first time, but with time the side of the gasket just burned away.
This is an old pic. The first set of gaskets that burned:


It was in. 2011. At this time I had thin washers inder the nuts. Changed to the OE thick washers but still 4 piece gasket kit. (Elring IIRC)
The second set was put on in 2016. Then I have planed the surface of the manifold as it was a bit warped and installed the one piece gasket. (Elring)


Now it is the third time. I will do it on the easter weekend.

Unless you get a machine shop to mill the port faces flat again, it won't seal properly. Exhaust manifolds can warp by whole mm from end to end so lapping wont remove enough metal or get accurate results.
All inline engines do this. Petrol, diesel, n/a and turbo and not just VW.

Talbot Express exhaust manifolds warp so much that they snap the studs. I lapped mine flat (emery cloth glued to a large 30mm thick steel engineers bench) and as above, it was easily 1mm out, if not more.
Since being lapped flat, it continued to warp and needed redoing after about 3 years.

silverbullet wrote: ↑10 Apr 2022, 09:02 Unless you get a machine shop to mill the port faces flat again, it won't seal properly. Exhaust manifolds can warp by whole mm from end to end so lapping wont remove enough metal or get accurate results.
All inline engines do this. Petrol, diesel, n/a and turbo and not just VW.

Yes it was warped quite a bit, but wit those big grinding wheels I did get them in plane. No feeler gauge did fit under the straight edge across. But did not measure the plane to the nut surfaces.

Do you use a support from the turbo to the engine block this may help there’s a lot pulling down on the exhaust manifold, the turbo and the exhaust the one in the photo is home made not by me I still need to do it

T25boy71 wrote: ↑11 Apr 2022, 10:20 Do you use a support from the turbo to the engine block this may help there’s a lot pulling down on the exhaust manifold, the turbo and the exhaust the one in the photo is home made not by me I still need to do it

Yes, I have modified the original bracket by lenghtening rhe oval holes.

The manifold is warped again.
0.4mm and 0.3mms on the ends.
Now I am lapping again with the grinding stones.
Done to half after a few hours
Pics later.

A few hours, a couple of beers and a load of elbow grease and managed to knock down to almost plane. Well under 0,5mm gaps, the light barely shines under the straight edge.
I hope it will be OK. 

I am not too comfortable with individual stoning of ports or use of straight edge alone. (OK Granny .)
In the absence of a large engineers surface plate and unintuatively, I have found a sheet of PLATE glass can be suitable if checked out first in all directions with said straight edge. Plus a sheet of plain paper layed onto your  lightly oiled surface plate will show any areas of uneven contact when you think you are done.
Heat distortion though - what a nightmare .

Mr Bean wrote: ↑13 Aug 2022, 10:08 I am not too comfortable with individual stoning of ports or use of straight edge alone. (OK Granny .)
In the absence of a large engineers surface plate and unintuatively, I have found a sheet of PLATE glass can be suitable if checked out first in all directions with said straight edge. Plus a sheet of plain paper layed onto your  lightly oiled surface plate will show any areas of uneven contact when you think you are done.
Heat distortion though - what a nightmare .

Oily paper is a good trick.
The stone I used is about a foot in diameter, so IMO it is enough.
Yet holds and looks OK, however not checked thoroughly around. But next time I will give it to a machine shop.

Silly question maybe, but I’m just curious as to whether you tried putting a straight edge on the engine ports as well?

If the tendency is for the two ends of the manifold to warp away from the block, as your experience seems to suggest, then maybe that would be compounded if the centre ports on your engine block were also slightly proud of the end ones.

No, I have not checked the head, but will do if the metal gasket also fails.