LO 8-1 Identify and describe the purpose and basic function of cylinder blocks and identify factors influencing current block design features and operation

1. The Evolving Cylinder Block

The Evolving Cylinder Block

The cylinder block is the largest engine component and forms the engine’s main structure to which all other major components attach Figure 1. It is called the cylinder block because it encloses the cylinders and cylinder components in a large, single-piece casting Figure 2. The engine crankshaft, bearings, flywheel housing, and cylinder walls (which includes replaceable cylinder liners) are integral components of the cylinder block. Diesel engine blocks have unique features. Due to their operating characteristics and high power output, which demand unique design and construction features, diesel engine blocks deliver the reliable economy and durable operation expected of them. Diesel engine cylinder blocks are a topic of practical interest to technicians because their construction features require specialized service techniques and diagnostic procedures. Unlike spark ignition engines, a diesel cylinder block is constructed to be repaired and rebuilt more frequently to renew its service life. Service practices can impact service life by extending it or by causing catastrophic failure if performed incorrectly.

FIGURE 08-1: The cylinder block forms the main structure of the engine. It encloses the cylinder components, and other major engine parts are attached to it.

FIGURE 08-2: An in-line six-cylinder engine block stripped of accessories.

One of the recent trends in engine technology is a greater emphasis on increasing engine power density; generating more power from increasingly smaller displacement engines is a major factor that influences contemporary features in diesel cylinder block design. New or improved construction features are needed to accommodate higher cylinder pressures that generate substantially more power output per unit of displacement. Combustion characteristics of diesels also produce extraordinary forces that distort the shape of connecting rods, bend crankshafts, and generate several types of intense, mechanical forces that require reinforcement of the block to increase its strength and rigidity Figure 3. The greatest of these forces is called torsional vibration, which is observed as rotational speed changes in the crankshaft taking place between each combustion cycle and revolution of the crankshaft. Compression and combustion events, which produce large swings in cylinder pressure, cause the crankshaft to speed up and slow down with each power and compression stroke. This means diesel cylinder blocks need additional devices to dampen potentially destructive combustion forces transmitted from the combustion chamber and throughout the engine. Technicians need to not only identify these devices and understand how they operate but also properly evaluate whether they are operating correctly and diagnose defective components when they are not.

FIGURE 08-3: The steel plate that joins both oil pan rails is used to add rigidity to this engine block.

FIGURE 08-4: Combining the use of a mono steel piston with a reduced piston skirt size minimizes friction against the cylinder walls.

When covering the topic of cylinder block construction in today’s engines, legislative demands to lower noise and greenhouse gas (GHG) and noxious emissions (while meeting rugged durability requirements for building engines) require the attention of the technician. To prevent increased fuel consumption and limit already difficult to detect emissions from exceeding certification limits, engines must be able to resist wearing out and perform with the same efficiency as a new engine throughout the engine’s useful life. These considerations make their way into not only service practices but also block construction through the use of new designs, construction materials, and techniques that reduce fuel consumption, engine friction, wear, and block weight Figure 4. Tighter engine operating clearances and the use of thinner, low-viscosity engine oils are features all technicians need to give special attention to, particularly in the latest engines.

Engine downspeeding is another operating strategy to reduce GHG and noxious emissions. Downspeeding involves intentionally lowering driveline gear ratios (even further than already traditionally low gear ratios) to take advantage of diesels’ high torque output at low engine speeds. The current trend of downspeeding engine operation improves engine efficiency. Unfortunately, it magnifies the effect of torsional vibration from diesel engines. Lower engine operating speeds, combined with high cylinder pressures, transmit an even greater degree of torsional vibration from the crankshaft to other crankshaft-driven loads, including the driveline.

Contemporary cylinder block features incorporate major revisions in engine technology, such as the use of overhead camshafts or features that accommodate newer emissions control system components. Recent refinements include relocation of camshafts and geartrains and the addition of balance shafts, new vibration dampers, and block materials. What all this means for technicians is that service techniques, diagnostic practices, and the type of service recommendations technicians should make are changing as cylinder block technology evolves and becomes more sophisticated. Technicians may not frequently perform service work directly on cylinder blocks, but the function of a block is deeply integrated with most other aspects of engine operation and this influences how other components are serviced. This chapter will provide fundamental information about cylinder blocks to enable technicians to develop relevant skills related to cylinder block service, maintenance, and diagnostic practices and to make correct service recommendations.

1.1. The Evolving Cylinder Block

One of the recent trends in engine technology is a greater emphasis on increasing engine power density; generating more power from increasingly smaller displacement engines is a major factor that influences contemporary features in diesel cylinder block design. New or improved construction features are needed to accommodate higher cylinder pressures that generate substantially more power output per unit of displacement. Combustion characteristics of diesels also produce extraordinary forces that distort the shape of connecting rods, bend crankshafts, and generate several types of intense, mechanical forces that require reinforcement of the block to increase its strength and rigidity Figure 3. The greatest of these forces is called torsional vibration, which is observed as rotational speed changes in the crankshaft taking place between each combustion cycle and revolution of the crankshaft. Compression and combustion events, which produce large swings in cylinder pressure, cause the crankshaft to speed up and slow down with each power and compression stroke. This means diesel cylinder blocks need additional devices to dampen potentially destructive combustion forces transmitted from the combustion chamber and throughout the engine. Technicians need to not only identify these devices and understand how they operate but also properly evaluate whether they are operating correctly and diagnose defective components when they are not.

FIGURE 08-3: The steel plate that joins both oil pan rails is used to add rigidity to this engine block.

FIGURE 08-4: Combining the use of a mono steel piston with a reduced piston skirt size minimizes friction against the cylinder walls.

When covering the topic of cylinder block construction in today’s engines, legislative demands to lower noise and greenhouse gas (GHG) and noxious emissions (while meeting rugged durability requirements for building engines) require the attention of the technician. To prevent increased fuel consumption and limit already difficult to detect emissions from exceeding certification limits, engines must be able to resist wearing out and perform with the same efficiency as a new engine throughout the engine’s useful life. These considerations make their way into not only service practices but also block construction through the use of new designs, construction materials, and techniques that reduce fuel consumption, engine friction, wear, and block weight Figure 4. Tighter engine operating clearances and the use of thinner, low-viscosity engine oils are features all technicians need to give special attention to, particularly in the latest engines.

Engine downspeeding is another operating strategy to reduce GHG and noxious emissions. Downspeeding involves intentionally lowering driveline gear ratios (even further than already traditionally low gear ratios) to take advantage of diesels’ high torque output at low engine speeds. The current trend of downspeeding engine operation improves engine efficiency. Unfortunately, it magnifies the effect of torsional vibration from diesel engines. Lower engine operating speeds, combined with high cylinder pressures, transmit an even greater degree of torsional vibration from the crankshaft to other crankshaft-driven loads, including the driveline.

Contemporary cylinder block features incorporate major revisions in engine technology, such as the use of overhead camshafts or features that accommodate newer emissions control system components. Recent refinements include relocation of camshafts and geartrains and the addition of balance shafts, new vibration dampers, and block materials. What all this means for technicians is that service techniques, diagnostic practices, and the type of service recommendations technicians should make are changing as cylinder block technology evolves and becomes more sophisticated. Technicians may not frequently perform service work directly on cylinder blocks, but the function of a block is deeply integrated with most other aspects of engine operation and this influences how other components are serviced. This chapter will provide fundamental information about cylinder blocks to enable technicians to develop relevant skills related to cylinder block service, maintenance, and diagnostic practices and to make correct service recommendations.