In the late seventies, Porsche increased the horsepower of their engines causing them to retain more heat than they had previously. At that time, Porsche engine blocks were made of Magnesium, and the cylinders were made out of Aluminum. Porsche attached the cylinders to the block with head studs made out of an alloy called Dilivar – specially designed to heat and cool at the same rate as Aluminum and Magnesium… Unfortunately, Dilivar did not work as well as our friends at Porsche would have hoped, and because of the different rates heating of Magnesium and Aluminum, when the cylinders and engine block heated up and expanded, the head studs would pull out of their threads in the engine block, and would not return when the engine cooled.  The engines would literally tear themselves apart after time.

Here we have a few images of what can happen when the heads begin to pull off of a 1977 Porsche 930 motor.

In this particular engine, the head studs had pulled out so far that the engine’s timing chain was pulled off of its guides and was riding on the bolts that held its guides and rubbing against the timing chain cover.

The expanding / contracting problem can become so bad that head studs will actually break… here are a few below.