Friday, May 18, 2012

Piston Engines Crankcase

This is the name given to that part of the engine that houses the crankshaft and connecting rods.  It provides mounting faces for the cylinders or cylinder blacks, reduction gear, wheel case and other units.  It may be a single casing or build-up of several sections depending on the type of engine.  It will contain the main bearings which are usually plain metal bearings for in-line engines and roller bearings for radial engines.  The engine mountings for in-line engines take the form of our feet and a steel ring is usually used for radial engines.  Provision is made at the lowest point of the crankcase for collection of engine oil for recirculation which is known as the engine oil sump
The crankcase is subjected to many variations of vibrational and other forces.  Since the cylinders are fastened to the crankcase, the tremendous expansion forces tend to pull the cylinder off the crankcase.  The unbalanced centrifugal and inertia forces of the crankshaft acting through the main bearing subject the crankcase to bending moments which change continuously in direction and magnitude.  The crankcase must have sufficient stiffness to withstand these bending moments without deflections or deformations.  If the engine is equipped with a propeller reduction gear, the front or drive end will be subjected to additional forces causing engine case to be more stressful.


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