Causes of engine failure
The major cause of engine failure can be lumped into four basic categories: See more at http://www.aa1car.com/library/us697.htm

Head Gasket Failures
Head gaskets can fail just because of engine design e.g hot spots or materials (cast jugs, aluminum head, etc) but, here are some of the reasons I'm concerned about:
Overheating
A very common cause of head gasket failure. If the engine gets hot enough, the cylinder head can swell to the point where it crushes the headgasket (usually betwen the cylinders). The extruded material and/or cracks then provide a leak path for coolant and/or combustion gasses.
Replacing the head gasket will cure the leak but not the problem.
Detonation & Pre-Ignition
Excess pressure in the combustion chamber is another common cause for head gasket failure.
Head Gasket Installation Errors
Head gaskets obviously require a clean, smooth, flat surface on both the cylinder head and block. While the head is off the engine, check the flatness of both the head and block. Use a straight edge and feeler gauges to check all critical areas, especially those between the cylinders.
Diagnosing Gasket Failures
Figuring out why a head gasket failed is the first step to preventing repeat failures. Sometimes the cause is obvious and sometimes it isn’t.

Brian Owens of ROL Mfg. of America, says his company has just p ublished a wall chart that illustrates the most common causes of gasket failure, which are detonation, overheating and incorrect torque. The chart lists the causes of each, along with recommended remedies.

One of the causes of overheating, for example, is a dirty cooling system. As little as 1/8 inch of calcium deposits in a radiator may reduce cooling efficiency by 40%. It’s also important to use the correct type of coolant and the proper mixture (50/50 is usually recommended for year-round driving).

Owens said "high temperature" gaskets are often a good solution for applications where a head gasket has failed due to detonation. These gaskets can provide additional sealing strength through the use of stainless steel fire rings and may include special beading and facings, often graphite. The gaskets will also lower compression radio slightly because they are slightly thicker than a stock gasket.

A head gasket that failed because of overheating or a hot spot will be crushed and measurably thinner in the damaged area when checked with a micrometer. By comparison, a gasket that has failed due to detonation or preignition will usually have cracked armor around the combustion chamber which leads to burn-through.

The corresponding surface areas on both the head and engine deck where the gasket failed should be inspected for damage (erosion, pitting or cracks) as well as flatness. If either surface is damaged or is not flat, the head and/or engine block must be resurfaced otherwise the new head gasket may not seal properly. While the head is off the engine, check the flatness of both the head and block. Use a straight edge and feeler gauges to check all critical areas especially those between the cylinders. Flatness specifications vary depending on the application, but Aluminum heads should have no more than .002 (.05 mm) out-of-flat in any direction in most cases