Engine Block Components

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Engine Block Components

Ready for Review

►   The engine block is the main structure of the internal combustion engine; it provides the engine’s framework and a mounting surface for all components.
►   The engine block is machined in one piece, with precise specifications that help to prevent air and fuel leakage, withstand the thermal stresses of combustion, and accommodate any resulting shocks and vibration from power pulses.
►   Engine block casting must accommodate cylinders and water jackets (passageways around the cylinders); this can be done with core sand or foam shapes.
►   Manufacturers are increasingly making aluminum alloy engine blocks, as they are lighter weight and increase fuel efficiency.
►   The engine block assembly (lower end) includes: oil galleries and plugs, water jacket and plugs, pistons and rings, piston pins, connecting rods and caps, rod bearing inserts, main bearing caps, main bearing inserts, the thrust bearing, crankshaft, rear seals, camshaft (in block cam), a vibration balancer, and smooth surfaces to accommodate mating parts.
►   Ribs, webs, and fillets provide reinforcement and strength to high-stress areas of the engine block.
►   The main bearing caps, which provide crankshaft support, are sometimes supported by a main bearing cap girdle (some of which are integrated).
►   Cylinders are either machined into the cylinder block or are made of a cast iron sleeve.
►   Cylinder sleeves are dry (not in contact with a water jacket; held by an interference fit), dry flange (also not in contact with a water jacket; locked into engine block with a flange), or wet (direct contact with water jacket coolant).
►   The piston fits into the cylinder and is responsible for transferring power stroke force to the crankshaft.
►   The piston assembly includes a head, skirt, pin, connecting rod, piston boss, compression rings, oil rings, piston ring grooves, ring lands, and wrist pin.
►   Piston slap occurs when there is too great a clearance between the piston and the cylinder wall.
►   Cam-ground pistons are slightly oval shaped to accommodate heat expansion.
►   Compression ratio refers to the difference between the volume in the combustion chamber above the piston when the piston is at bottom dead center and the volume of the combustion chamber above the piston when the piston is at top dead center.
►   The compression ratio can be changed by altering the shape of the piston head (e.g., flat, concave, dome-shaped, recessed, machined reliefs).
►   Pistons can be manufactured via forging (more expensive, but stronger) or casting (cast aluminum or hypereutectic).
►   Piston skirts may be coated with ceramic or molybdenum disulfide to reduce friction with the cylinder wall.
►   Piston compression rings must have proper end gap, back clearance, and ring tension.
►   Connecting rods are H- or I-beam shaped and types include cast, forged, aluminum, and powdered metal (most recent technology); rod caps are not interchangeable among the different types.
►   The crankshaft is designed to transform piston stroke power into rotary motion.
►   The crankshaft assembly contains main bearing journals that help to center the crankshaft at the bottom of the engine block, where they mate with main bearings.
►   Crankshafts may be internally or externally balanced, using counterweights.
►   Crankshaft bearings are split in two parts, each with a tang that fits into the bearing saddle and cap.
►   A thrust bearing is used to limit end play movement of the crankshaft.
►   An oil hole in the main bearing saddle allows oil from the oil gallery to lubricate the main bearings.
►   Bearings can be undersized or standard and are generally either trimetal or bimetal.
►   An engine will have either a flywheel (manual transmission) or flex plate and torque converter (automatic transmission) to store rotational energy.
►   The harmonic balancer (crankshaft damper) reduces vibration from the piston and crankshaft assembly.
►   Crankshaft seals are designed to contain lubricating oil.
►   Balance shafts reduce engine vibrations and may use counterweights to reduce second-order vibrations.
►   Stock compression ratios typically run between 8:1 and 10.5:1 and can be intentionally increased if necessary.
►   When disassembling the engine, refer to manufacturer’s service information.

Source : http://www.cdxauto.com/cw/fundamentals/docs/24118_CH13_Ready%20for%20Review.doc

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