This article is one in a series that have been released in conjunction with Wayne's book, 101 Projects for Your Porsche 911. The book contains 240 pages of full color projects detailing everything from performance mods to changing your brake pads. With more than 650+ full-color glossy photos accompanying extensive step-by-step procedures, this book is required reading in any Porsche 911 owner's collection. See The Official Book Website for more details.
One of the most popular upgrades to the 911 engine is the installation of the 911 turbo valve covers. The valve covers originally installed on almost all 911s from 1968 through 1977 were manufactured out of magnesium. The magnesium was originally used to cut down on the overall weight of the engine. Unfortunately, the magnesium covers were a poor match for the 911 engine and its stressful environment. It is very common for the magnesium valve covers to warp after many years of temperature cycling in the normal operation of the engine.
As the valve covers leak, the oil will spill onto the tops of the heat exchangers, causing the car to smoke a bit when driving. You may also notice the smell of burning oil as the heat from the exhaust burns away the oil on top of the exchangers. If oil is dripping from the cam towers, then chances are your valve covers are indeed leaking. If not, then you might have an oil leak coming from somewhere else. See Project 21 for more information on fixing these other oil leaks.
As original equipment, the magnesium valve covers were bolted to the aluminum cam towers of the engine. No one can quite agree on what causes the warping, however, this inevitably leads to the valve covers leaking. While replacing the valve cover gaskets with better silicone beaded ones may help the problem, the best solution is to replace the covers entirely with what has come to be known as the 911 Turbo valve covers.
First used on the 911 Turbo (930), these covers are made entirely of aluminum. The aluminum covers are stronger and less likely to corrode than their magnesium counterparts. Additionally, the late-model lower Turbo valve covers are reinforced with aluminum ribs that stiffen and support the structure of the cover, further decreasing the likelihood of warping.
If your 1968 and later 911 is equipped with the original magnesium covers, then you should definitely upgrade both the upper and lower covers to the later style Turbo aluminum covers. For cars manufactured after 1978 and later, I recommend that you replace your lower valve covers with the reinforced Turbo ones. The upper valve covers on these 911s were already cast out of aluminum.
To check to see if your original magnesium covers (darker in color than the aluminum ones) are warped, place them on a flat surface (glass table) and see if they rock back and forth. If they do, then you should most certainly replace them with the improved aluminum 'Turbo' valve covers.
The installation of the covers is a bolt-on process, and no modifications are required. Simply remove the old valve covers and replace them with the new ones. Make sure that you use new valve covers gaskets, and torque the nuts down on the valve covers to about 8 Nm.
If your car still leaks even with the installation of the Turbo valve covers, you might want to take them to your local machine shop and have them milled flat. Sometimes the casting process used in manufacturing the covers can leave them slightly deformed. Milling the mating surface assures that they will be completely flat when bolted to the car. This can also work to resurrect the early 1965-67 valve covers as well.
Stiffening ribs on the Turbo valve covers strengthen the lower valve covers and reduce the chance of warping. The additional heat from the engine's exhaust system necessitates the need for this additional stiffness. For a photo of the magnesium valve covers, see Figure 1 of Pelican Technical Article: Changing Engine Oil.