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Chapter 4 Cylinder Blocks and Crankshafts
cylinder block, which in turn will increase rigidity to resist bending and noise generating vibration as the power strokes on the crankshaft transmits energy capable of distorting bearing bores.
Deep-Skirt Blocks
FIGURE 4-18 Deep-skirt blocks extend the block walls
below the main bearing caps. Note also the direction indicators for the road bearing caps point toward the front of the engine.
Anchor Bolts to Main Bearing Cap Oil Pan Rails
Reinforcing Steel Bedplate
A deep-skirt block is a design that refers to a block configuration where the bottom edge of the block or crankcase walls extends well below the crankshaft’s centerline (FIGURE 4-18). The sides of the crankcase are separated from the main bearing caps to minimize transmitting the noise produced by combustion events out from the main bearing caps. Bearing caps are held in place with two or four vertically placed bolts. Lengthening the block walls below the main bearing caps enhances structural rigidity and operating smoothness which allows for a larger mating surface with the transmission. A reinforcing steel plate may also be attached to the oil pan rails and main bearing caps to enhance rigidity and strength of the block. The plate, whose thickness is approximately ⅜"–½" of steel, ties the oil pan rails to the main bearing caps to add further structural rigidity to the block (FIGURE 4-19). Reducing vibration and increasing block rigidity can be further enhanced by adding curves to the deep-skirt crankcase walls. Also known as serpentine convolutions, the curves make the crankcase less flexible than flat surfaces would be. Adding ribs and webbing to the crankcase area is a design technique that minimizes crankcase distortions that would cause noise vibration and harshness in all types of blocks (FIGURE 4-20).
Crossbolted Blocks FIGURE 4-19 A steel bedplate attached to the oil pan rails and
the main bearing caps of this high-torque-output, deep-skirt engine block adds extra rigidity and strength to the block.
Advancing beyond the traditional deep-skirt block technique is the crossbolted block. Also known as tie-bolted or bolster-bolted blocks, this design uses additional horizontal placed bolts to connect crankcase walls of the block to the main bearing caps (FIGURE 4-21). Crossbolted
Closed Block Deck
Crossbolted Block FIGURE 4-21 A crossbolted main bearing cap in an aluminum
FIGURE 4-20 The crankcase of this 5.0 L Cummins diesel used
by Nissan pickups has a serpentine wall. The design adds rigidity and strength to its deep-skirt design.
block with cast iron liners. Horizontal crossbolts or tie bolts attach the main bearing caps to the crankcase wall. A pair of vertical bolts also ties the main bearing cap to the block. Crossbolting is used to enhance engine block strength and rigidity while reducing noise and lowering engine weight.
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