The crankshaft fits into the bottom of the engines block. Engine crankshafts are usually made of cast iron or forged steel. Forged steel are needed for heavy duty applications, such as turbo charged or diesel engines. A steel crankshaft is stiffer and stronger than a cast iron crankshaft. It will withstand greater forces without flexing, twisting or breaking. Oil passages leading to rod and main bearings are either cast or drilled in the crankshaft.
Oil enters the crankshaft at the main bearings, and passes through holes in the bearing journals. It then flows through passages in the crank and out to the connecting rod bearings.
With an in-line engine, only one connecting rod fastens to each rod journal. With a V type engine two connecting rods bolt to each crankshaft journal. The amount of rod journal offset controls the stroke of the piston. The journal surfaces are precision machined arid polished to very accurate tolerances. The crankshaft main journals are the surfaces that are precisely machined and polished to fit into the block main bearings.
The crankshaft- rod journals are also machined and polished surfaces. But they are offset from the main journals. The connecting rods boll to the rod journals with the engine running, the rod journals circle around the centerline of the crank. Counter weights are formed on the crankshaft — to prevent vibration. The weight counter- acts the weight of the connecting rods, pistons, rings and rod journals off set. The crankshaft-snout sticks through the front of the block. It provides a mounting place for the crankshaft — drive mechanism, front dampers and fan belt pulleys.
A flange for holding the flywheel is the hack of the crankshaft. The flywheel bolts this flange. The center of the flange has a pilot-hole or bushing for the transmission torque converter or input-shaft.
Automobile engines normally have 4, 6, or 8 cylinders. The crankshaft — rod journals are arranged to that there is always at least one cylinder on power stroke. Then, force is always being transmitted to the crankshaft to smooth engine operation.
It is made very stiff, since it is subjected to sever and varying twisting stresses due to the explosion pressure and also to the ‘inertia’ effects of reciprocating pans, the later effects are the forces due to the acceleration and deceleration of the piston and connecting rod in their strokes.
The twisting or turning action on the crankshaft, which is generally spoken of as the torque, is constantly changing: this fact necessitates a stronger shaft than for a steady motion. The firing stroke gives the greatest torque. In order to reduce this great variation of torque, which puts severe stress on the driving and driver members of the automobile, it is usual to employ a number of smaller cylinders so that maximum values of the torque are correspondingly lower, and occur more frequently. The greater the number of cylinders the smoother becomes the torque distribution.
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