Softness Of Aluminium Heads
Aluminium has different chemical properties to cast iron and it is known that it expands and contracts quicker when it heats up and cools down.
Aluminium heads are common components in modern engines mainly due to the weight advantage they have over cast iron heads. The weight of the vehicle is a major factor a manufacturer will consider in design. A lighter vehicle requires less force to drive it and is therefore more efficient to run. Try picking up an aluminium head and then a cast iron head - you will certainly notice the difference!
A change in construction material of a component means that different elements need to be considered when reconditioning the engine. Aluminium has different chemical properties to cast iron and it is known that it expands and contracts quicker when it heats up and cools down. This quicker cycle of expansion and contraction can cause the material to become stressed. Particularly in cases where the engine has experienced extreme temperatures, such as when it has been overheated, the aluminium changes its characteristics and becomes "annealed" (loses its hardness). It is vital that a "soft" aluminium head is not reused as it is impossible to achieve a correct seal between the head and the block. This is basically due to the fact that the metal in the head has lost its strength, and subsequently, its ability to clamp effectively. An improper seal means head gasket failure which could cause considerable damage to your engine. The cost of rebuilding an entire engine is not worth risking for the simple process of checking the head first.
At Galloway Engines, we use a digital hardness test to ensure that aluminium heads meet the vehicle manufacturers' specifications. Manufacturers use a variety of metals and composites in their castings and consequently heads anneal at different temperatures. If your engine has been overheated, your head is showing signs of being "soft" or you would like the reassurance of knowing that you are not going to have future problems, call in and see us at Galloway Engines, and we can perform a quick test to determine the condition of your aluminium head. Piece of mind is as easy as that!
