Heat

Abstract

Thermal expansion is the ability of many materials to expand when heated, and then contract again when cooled. The degree of expansion depends upon the temperature rise and the type of material. Steel has a lower expansion than aluminium alloy, therefore if new pistons are to be fitted they may be placed in very hot water for a short period and on removal the steel gudgeon pins may be pushed out quite easily. The procedure can be repeated when the pins are to be replaced. Starter rings are heated uniformly and then placed on the machined section of the flywheel, and as the ring cools it will create a highly compressive force radially thus gripping the flywheel tightly. Refrigeration or liquefied gas such as liquid nitrogen is frequently used to fit such items as valve guides, bushes, cylinder liners, etc. When placed or lightly pushed into position they expand as they return to room temperature and thus fit tightly as if they had been driven or pressed in with an interference fit requiring considerable force.