Chapter 08: Final Review & Key Terms

1. Ready for Review

• The cylinder block is the largest single part and main structure of the diesel engine, and its primary function is to support cylinders and liners (if equipped) and major engine components, including the crankshaft and the camshaft.
• Diesel engine blocks have cylinders arranged either in-line, V-banked, or horizontally opposed and can be configured with different numbers of cylinder bores.
• Cylinder blocks can be constructed from cast iron, aluminum, or compacted graphite iron; each of these materials has advantages and disadvantages.
• Primary balance, which is achieved when the crankshaft counterweights offset the weight of the piston and connecting rod assembly, and secondary balance, which is achieved when the movement of one piston counterbalances the movement of another, result in smoother-running engines.
• The main purpose of the crankshaft in a reciprocating engine is to convert the linear motion of the connecting rod assemblies to rotational movement.
• The mechanical stresses placed on a crankshaft require it to be especially strong, so crankshafts are hardened to improve durability; the two most common processes are induction hardening and nitriding.
• Engine oil is used to lubricate, cool, and clean the crankshaft journals and bearings.
• To control the destructive effects of both torsional and harmonic vibrations, diesel engines are equipped with vibration dampers.
• Blocks must be designed to be as compact as possible to reduce weight and size while maintaining strength and rigidity; common block designs include deep-skirt blocks, cross-bolted blocks, ladder-frame blocks, and tunnel-bore blocks.
• There are several different configurations for engine block cylinders; which one is best depends on the vehicle’s application, production cost, and expected vehicle life cycle.
• Replaceable cylinder sleeves enable a worn-out engine to be quickly rebuilt and restored to factory specifications.
• Bearings perform important functions inside the engine, including reducing friction, supporting moving parts under load, and serving as replaceable wear surfaces.
• The characteristics important for engine bearings are compatibility, fatigue strength, conformability, and embedability; a variety of construction techniques are used to achieve different balances among the characteristics that will adapt to each engine’s unique operating conditions.
• The amount of oil clearance between the rotating shaft and the engine bearing is important for maintaining the hydraulic pressure of the oil wedge that cools and lubricates these parts.
• Bearings must not move within the bearing bore and must have good contact within the bore for proper heat transfer.
• Thrust bearings control end play in a crankshaft.
• The fit of a liner into the cylinder block is critical to engine operation; improper fit can produce various leaks and cause premature, if not catastrophic, damage to cylinder components, such as pistons and rings.
• Adequate piston skirt clearance must be maintained between the liner and the piston to allow for normal expansion of the piston when the engine is running at operating temperature.
• Wet liners protrude or extend above the cylinder block deck to project clamping forces from the cylinder head onto the liner flange and hold it in place; measuring and adjusting protrusion is one of the most critical operations when rebuilding a sleeved engine.
• Top-stop flange breakage is usually caused by excessive flange loading because of significant pressure that was applied to the flange through the cylinder head clamping forces.
• Cylinder block walls progressively wear with increasing engine hours and distance traveled; a dial bore gauge is used to measure cylinder wear resulting from taper.

1.1. Key Terms

cavitation erosion Pinholes produced in cylinder block walls, heads, and liner sleeves as a result of the collapse of tiny water vapor bubbles formed when coolant vaporizes on hot cylinder wall surfaces.

compacted graphite iron (CGI) A material produced from powdered iron alloys squeezed into molds at high pressures and then heated to bond the metal particles together; also known as sintered graphite.

cross-bolted block A variation of the deep-skirt block that uses additional horizontally placed bolts to connect the crankcase walls of the block to the main bearing caps; also known as a tie-bolted or bolster-bolted block.

deep-skirt block A block configuration with a bottom edge that extends well below the crankshaft’s centerline.

downspeeding An operating strategy to further reduce engine speed by intentionally lowering driveline gear ratios (even further than already traditionally low gear ratios) to take advantage of diesel’s high torque output at low engine speeds.

dry sleeve cylinder block A block designed with a bored or honed hole in the block that allows no coolant contact with the cylinder sleeve.

dual mass flywheels (DMF) Two-piece flywheel designs that incorporate specialized torsional damping springs.

fillet radius A circular machining applied to the surface between the journal and the crankshaft cheek that strengthens the crankshaft and minimizes the possibility of a fracture.

harmonic vibration A vibration that sends pressure waves moving back and forth along the axis of a shaft, particularly the crankshaft.

induction hardening A heat treatment process that involves passing alternating electric current through coils of heavy-gauge wire surrounding the material to be hardened; through magnetic induction, heat is produced in the metal, which is then quenched with water to produce a hard, wear-resistant metal surface.

ladder-frame block A block design with sides that extend exactly to the centerline of the crankshaft bearings and a separate, additional section that attaches to the crankcase and the oil pan and incorporates the main bearing caps into a one-piece component.

Nanoslide technology A plasma-spray welding technique developed by Mercedes-Benz to coat cylinder walls with a tool-grade hardness iron alloy.

nitriding A crankshaft hardening technique that involves heating the shaft and introducing cyanide salt or liquid into the heating chamber with the crankshaft; slowly cooling or quenching the crank with these substances in its heated condition causes the nitrogen and carbon to molecularly bond with metal surfaces to create an extremely hard journal.

parent bore block A block design that has holes cast and bored in the block for the cylinders with the pistons inserted directly into these holes; also known as a no-sleeve block.

pendulum vibration absorber A damper that provides torsional vibration control by producing forces that directly cancel the forces producing torsional vibration.

physical vapor deposition (PVD) A process used to add layers of new, hardened polymer coating to the surface of a plain bearing.

primary balance The balance achieved when the crankshaft counterweights offset the weight of the piston and connecting rod assembly.

scissor gear Two separate spring-loaded gears incorporated into a single unit to reduce gear rattle caused by torsional vibration.

secondary balance The balance achieved when the movement of one piston counterbalances the movement of another, resulting in smoother-running engines.

sputter-coated engine bearings Also called a sputter bearing , it is a bearing using a hardened overlay material using physical vapor deposition. This bearing has one of the highest capabilities to support a load compared to other bearing technologies.

tension bolts A feature of aluminum block construction where a single bolt is used to clamp both the cylinder head and the main bearing caps together.

torsional vibration The speeding up and slowing down of the crankshaft caused by alternating compression and power strokes of the engine cylinder.

tunnel-bore block A block that has the main bearing bores and block formed into one solid structure for maximum block rigidity and strength.

warp anchor A block design that has the cylinder head and the cylinder block bolted together by tie bolts; sliding steel sleeves, which are locked in the block, accept the cylinder head bolt from one side and the tie bolt from the other.

wet sleeve block A block designed with large holes into which the cylinder sleeves are inserted; coolant has direct contact with the outside of the sleeve and there is no supporting cylinder bore structure.