Bearing Characteristics

Engine bearings must operate under tremendous loads, severe temperature variations, abrasive action, and corrosive surroundings. Essential bearing characteristics include the following.

BEARING LOAD STRENGTH is the ability of a bearing to withstand pounding and crushing during engine operations. The piston and rod can produce several TONS of downward force. The bearing must not fatigue, flatten, or split under these loads. If the bearing load resistance is too low, the beating can smash, fail, and spin in its bore. This ruins the bore or the journal.

BEARING CONFORMABILITY is the ability of a bearing to move, shift, conform to variations in shaft alignment, and adjust to imperfections in the surface of the journal. Usually, a soft metal is placed over hard steel. This lets the bearing conform to the defects in the journal.

BEARING EMBEDABILITY refers to the ability of a bearing to permit foreign particles to become embedded in it (fig. 3-72). Dirt and metal are sometimes carried into the bearings. The bearing should allow the particles to sink beneath the surface into the bearing material. This prevents the particles from scratching, wearing, and damaging the surface of the crankshaft or camshaft journals.

BEARING CORROSION RESISTANCE is the ability of a bearing to resist corrosion from acid, water, and other impurities in the engine oil. Combustion blow-by gases cause engine oil contamination that can also corrode engine bearings. Aluminum-lead and other alloys are commonly being used because of their excellent corrosion resistance.