Thread: Problems with aluminum valve covers

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I had a leak at the back of the motor one time many years ago (oil on the floor) and was thinkin' it was the rear main seal. After cleaning up the mess and running it while paying attention, I realized that the oil was coming from around the black rubber seal between the bottom of the manifold and the top of the rear china wall. After talking to some buddies, I learned that they didn't use those cheezy, fosdick seals any more. They just squirted a fat bead of silicone across the china wall front and rear and sat the intake manifold down on that. I've been doing it that way ever since.

Not to say it can't be leaking from somewhere else, but I am almost positive it is the rear seal. It doesnt seem to be leaking from the distributor or the back of the intake (as it looks strikingly clean). I just know that if you arent getting good enough ventilation out of your air breather, the vaccum pressure will seek out any weak spot or holes it can find, thus pushing out oil. :/

I chased an oil leak on my SBF, and even went to the trouble of pulling the pan and replacing the gasket, thinking it was leaking around the rear main. I finally realized that my oil was coming from 1) the breather caps (no PCV), and 2) the fact that the valve cover only met the mating surface of the aluminum heads about 1/16", and the thick rubber gasket was rolling with torque (a stock FelPro gasket overlapped the top edge of the heads, but the bottom edge of the covers). I replaced the cast covers with a pair of fabricated covers made by the head supplier, and made sure that they had baffles at the ports on both sides. I replaced one breather with a fill plug, and the other with a direct mount PCV. Oil leak solved. The lack of baffle plates was a big part of the problem, but the mismatch in mating surfaces was the killer.