The oil in the engine does more than simply cut down friction and wear by lubricating the pistons, bearings and other moving parts. It also helps to seal hot high-pressure gases; takes heat away from hot areas and disperses it into the air in the sump; reduces corrosion; and absorbs some of the harmful waste products of combustion.

The oil is carried in the sump, at the bottom of the engine, and forced by a pump through a filter to the main bearings. From the main bearings, the oil passes through feed-holes into drilled passages in the crankshaft and on to the big-end bearings of the connecting rod.

The cylinder walls and gudgeon-pin bearings are lubricated by oil fling, oil escaping from the ends of the bearing and dispersed by the rotating crankshaft. A bleed or tributary from the main supply passage feeds each camshaft bearing. Another bleed supplies the timing chain or gears on the camshaft drive, and in some cases supplies the chain tensioner. The excess oil then drains back to the sump, where the heat is dispersed to the surrounding air.

Circulation of Oil in the Engine

Lubrication reduces friction and heat as well as minimises wear. The oil is delivered under pressure by a mechanically driven pump, from the supply in the sump to the moving parts of the engine.

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