Crankshaft Nomenclature




Crank-throw.

This is the distance from the main-journal centers to the big-end-journal centers. It is the amount the cranked arms are offset from the center of rotation of the crankshaft. A small crank-throw reduces both the crankshaft turning-effort and the distance the piston moves between the dead centers. A large crank-throw increases both the leverage applied to the crankshaft and stroke of the piston.

Crank-webs.

These are the cranked arms of the shaft, which provide the throws of the crankshaft. They support the big-end crankpin. They must have adequate thickness and width to withstand both the twisting and the bending effort, created within these webs. But their excessive mass causes inertial effect, which tends to wind and unwide the shaft during operation.



Main-bearing Journal.

Main-journal is the parallel cylindrical portions of the crankshaft, supported rigidly by the plain bearings mounted in the crankcase. The journals diameter must be proper to provide torsional strength. The diameter and width of the journal should have sufficient projected area to avoid overloading of the plain bearing.


Connecting-rod Big-end (Crankpin) Journals.

These journals have cylindrical smooth surfaces for the connecting-rod big-end bearings to rub against.

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