What IS a head gasket?

The internal combustion engine is constructed of many layers: bearing ladder, block and cylinder head. The K-series engine installed in the MGF/TF is no different, although perhaps a little more complex. Illustrated in the figure opposite is the cylinder head and block. Between these layers there is a gasket. The gasket is inserted to ensure adequate sealing between metal mating surfaces to prevent leakage of fluids and gases.

There is a gasket between the cylinder block and the cylinder head (shown in figure opposite, right). This gasket plays a vital role - not only prevent the seepage of oil (as with the gasket found between the sump and main bearing ladder), but also of coolant and combustion gases - the latter of which is at very high temperature and pressure.
If the gasket fails, then oil, coolant or combustion gases may be able to escape, with potential dire consequences to the engine:

• loss of compression in one or more cylinders, causing a misfire and loss of power.
• loss of coolant, and subsequently overheating of the engine (which, with an alloy design such as the K-series, will cause extensive damage and warping of the head and other castings)
• loss of oil lubrication, with potential damage to the reciprocating and rotating internal components of the engine.
• Mixing of oil and coolant, causing the oil to emulsify. The ensuing sludge does not circulate well, and causes overheating.

If, for any reason a head gasket failure is suspected, immediately switch off the engine and seek expect advice.

A head gasket failure (HGF) is said to occur when there is a breech of the gasket, allowing the escape and potentially mixing of water, oil and combustion gases. Opposite shows an engine being stripped down following an HGF. In the oil galleries, instead of normal brown honey-coloured oil, there is brown emulsion everywhere, signifying a failure of the gasket between the oil and coolant passage ways. This engine will need its oilways and cooling system throughly flushed out before reassembly.