LO 8-4 Explain the purpose and methods used to increase the rigidity and strength of a diesel engine cylinder block

LO 8-04: Explain the purpose and methods used to increase the rigidity and strength of a diesel engine cylinder block.

Crankcase Construction

High cylinder pressures, combined with tension and compression forces from rapidly accelerating and decelerating cylinder components, generate strong torsional vibrations. These forces bend and twist the crankshaft, and cylinder pressures work to separate the crankshaft from the block, pushing the crank out through the bottom of the block, along with the main bearing caps holding the crank in place. Blown engines at tractor pulling contests frequently provide clear evidence of the enormous combustion forces acting to split a cylinder block from the crankshaft. Stronger and more rigid block designs that are naturally heavier are needed to prevent destruction of the engine and to minimize transmission of forces into the block. Opposing this is the need for lightweight, durable designs necessary for engines to perform well under all operating conditions. The best solution for achieving quiet, smooth engine operation of a highly stressed block is a strongly reinforced crankcase Figure 24. Increasing the block strength and rigidity in the crankcase area allows the block to be as compact as possible while reducing its overall weight and size. Unnecessary weight is also the enemy of hauling heavier revenue-generating payloads, good vehicle braking, and precise handling characteristics. Several cylinder block designs, examined in the next sections, take different approaches to reinforcing the crankcase to rigidly retain the crankshaft in its place.

FIGURE 08-24: An example of a conventional cast iron block design. The block walls extend only to the main bearing caps to reduce the height of the block. The oil pan forms most of the crankcase boundaries and reinforces the block strength.

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