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.
