I think Peter Davis has it right, the key to stopping alloy valve cover oil
leaks is having an absolutly flat gasket surface. When I first made the
finned covers for the six cylinder engine I flatened the base on a large belt
sander as I have always done with the four cylinder covers. The six covers
are longer than the sander so I moved them back and forth. This cleaned them
up fine but if the casting had a little warp it would follow the warp and not
leave a flat surface. I shipped four or five of these before I got in use
feedback and discovered the problem. The solution was to set each one up on
the mill and machine the surface flat. This added to the finishing cost which
I wasn't happy about but was the right thing to do. The gasket surface of the
head is machined at the factory. The cast aluminum is very stiff and if
machined flat puts the gasket between two parallel ridged surfaces, the right
conditions for a good seal. All you need is a thin coat of the sealant of
your choice to stick the gasket to the valve cover for ease of reuse when
removing and replacing the cover. Some sheets of 80 or 100 grit wet or dry
glued on a good flat surface larger than the valve cover would do it with a
careful hand. Be careful not to rock the part as you go. If there is a big
gap, .020"+ you might want to get it on a mill as the hand sanding is slow
going.
I hope this helps
Ray Juncal
healeyray.com
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