The Cylinder Block, Crankcase, and Connecting Rods

Abstract

of a typical modern four-cylinder overhead valve engine is shown in Fig. 5.1. It can be seen that it is a fairly large casting that carries a large number of other items and, in fact, forms the basic structure of the engine. As such, the front of the block has to carry the loads imposed by the two mounting points of the engine unit and the rear of the block carries the gearbox, which has a single support at its rear. Therefore the crankcase walls usually extend well below the centre line of the crankshaft, in order to give rigidity to the block and ample support to the gearbox. This latter point is most important, as the joint is approximately half-way between the front and rear mounting points and thus at the point of maximum bending load. These mounting points have to take all loads from the power unit, including combustion reactions, transmitted through the block. In the earliest engines the cylinders were made separate from the crankcase, and were just cooled sleeves between the crankcase and the cylinder head. The modern crankcase, in addition to its obvious functions as the main structural member in the engine, also carries the camshaft and its drive (usually at the front in its own compartment), the water pump, the oil pump and its drive, the distributor and drive, the dynamo and the starter. It is drilled and cored for the circulation of oil and water.