Graphite Cylinder to Head Rings

[mrmoots]

I have assembled the cylinders, heads and cam carriers to my 964 in accordance with Waynes book and the factory manual.

I am using a Wrightwood racing gasket set, which comes with graphite cylinder to head sealing rings. I have just noticed a very fine gap between the heads and cylinders, it is enough just to wiggle a 0.05mm feeler gauge blade into. The blade stops when it hits the sealing ring. I cannot get the blade in where the head studs are, just in the centre positions.

Is this correct? It’s the same on both cylinder banks. It clearly shows the ring does the sealing, but surprised it supports the entire head and cam assembley as well.

This morning I have pulled the head and cam assemblies off of cylinders four to six. The grove in the cylinders is 1.51mm whereas the uncompressed ring is 1.60mm. With the rings removed and the head only resting on the cylinders, not torqued down, there is no gap.

You can see the mark the graphite ring has left on the heads, but cannot see and other marks. Looking at others photos when they pulled their engines apart, you can distinctly see the marks on the heads that the cylinders and sealing rings have made.

I have now refitted everything and torqued back up again and the gaping is identical.

Do you think the ring will compress when the engine is up and running so I can retorque the heads after say 500miles?

Thanks

[Jeff Jagusch]

While I am not an expert in this application, I have worked in the gasket industry as an engineer for over 20 years

If I understand your concern, you are seeing the .05mm or .002" bending of the heads with the gasket installed.
The reason you have no gap at the studs is that the heads are bending slightly.
This is as to be expected and most likely acceptable. As much as you would think that the head is completely rigid, there will be some bending

My guess is that once you run the engine at temperature the gasket will compress a bit more due to the differential in thermal expansion between the aluminum cylinder and head and the head studs. If you recheck for the bending, it may disappear?

The typical gasket design using a graphite (or any fiber based material for that matter) material does not rely on a specific compression established by the joint (the 1.51 groove in your head) but rather the compression of the gasket itself. This is primarily due to the difficulty in managing the tolerances of the groove and the gasket thickness. Having said that Porsche tolerances are probably closer than most, and thats why you are seeing the small gap.

Hope this helps a bit?


Jeff