Engine crankshafts rotate at very high speeds, necessitating the use of bearings to reduce friction and resistance. However, the bearings used on crankshafts are quite special and completely different from the bearings we see every day.
Most people are familiar with ball bearings, as shown in the picture above, which are widely used in automobiles. They can be found in parts such as gearboxes, wheels, water pumps, air conditioning compressors, and car alternators.
However, crankshafts use a different, less common type of bearing: two semi-circular metal plates, technically called sliding bearings. Because they resemble roof tiles, they are commonly referred to as "bearing shells."
From their appearance alone, many people would never guess that bearing shells have anything to do with reducing friction. But this type of bearing is used on engine crankshafts, and it is also the sliding bearing used between the crankshaft and connecting rods.