Engine Components • Four-Stroke Cycle Engines • Engine Output Engine Operation Engine Components • Four-Stroke Cycle Engines • Engine Output

Competencies List the components of an engine block. Describe a cylinder head. Explain the operation and components of a crankshaft. Describe pistons and piston rings. Explain the function of connecting rods and bearings.

Competencies Describe the flywheel and valve train. Compare the operation of four-stroke cycle and two-stroke cycle engines. Describe valving systems. Explain important features of diesel engines. Explain measurement of engine output.

How it works The internal combustion engine converts potential chemical energy into mechanical energy Is done by heat derived from a fuel source Approximately 30% of energy released in engine is converted into work Remaining energy lost in form of heat & friction in engine

It’s Got To Hold Up Components are designed to convert energy for maximum efficiency They must withstand heat and stress generated inside engine during operation Must meet size and weight requirements

Engine Blocks cylinder block crankcase cylinder bore cooling fins valve train components crankcase Engine components commonly required in reciprocating engines include the engine block, cylinder head, crankshaft, piston and piston rings, connecting rod, bearings, flywheel, and valve train. The engine block is the main structure of an engine and consists of a cylinder block and a crankcase. Figure 3-1. The cylinder block consists of the cylinder bore, cooling fins (on an air-cooled engine), and valve train components, depending on the engine design. An air-cooled cylinder block has cooling fins on the exterior, which are thin, cast strips designed to dissipate heat away from the engine cylinder block. The crankcase houses and supports the crankshaft and acts as an oil reservoir in four-stroke cycle engines. The crankcase has a crankcase breather that functions as a check valve and may also have a sump and a crankcase cover. Figure 3-3. Cylinder blocks may be aluminum for light weight, cast iron for wear resistance, or aluminum with cast iron cylinder sleeves. Figure 3-4.

Engine Block Main structure of engine Supports & maintains alignments of internal & external components Block can be produced as one-piece or two-piece unit

Cylinder Bore Hole in block that aligns and directs piston during movement

Stroke Stroke is the linear distance the piston travels in bore from top dead center (TDC) to bottom dead center (BDC) TDC point in which piston is closest to cylinder head before piston moves back down cylinder BDC point which piston is farthest from cylinder head before piston moves back up cylinder

Displacement Displacement (swept volume) that a piston displaces in an engine when it travels from TDC to BDC during same piston stroke

Calculating Displacement When bore and stroke are known then displacement can be found D=.7854 * B2 * S D = displacement (in cubic inches) .7854 = constant B2 = bore squared in inches S = Stroke in inches

Displacement Example An engine has a 2.5” bore & a 2” stroke. Figure out displacement: D=.7854 * (2.5*2.5) * 2 D = .7854 * 6.25 * 2 D = 9.8175 D = 9.82 cubic inches

One More Time!! What is the displacement of a single-cylinder engine that has a 3.25” bore and a 3.375” stroke? D = .7854 * (3.25*3.25) * 3.375 D = .7854 * 10.5625 * 3.375 D = 27.9982 D = 28 cubic inches

Do That Times 2 For multiple-cylinder engines: Multiply the displacement of the single-cylinder by the total number of cylinders Generally, the larger the displacement, the more power it can produce

Air vs. Liquid Cooled Air cooled engines Have cooling fins on exterior of block Thin cast strips designed to provide efficient air circulation & head dissipation away from block into air stream Increases surface area of block contacting ambient (existing) air for cooling efficiency Fins cast into or bolted onto flywheel act as fan blades & give air circulation around block & head

Air vs. Liquid Cooled

Air vs. Liquid Cooled Liquid cooled engines Have channels (sleeves) drilled or cast into block to allow coolant to pass through engine and cool it Similar to engine in automobile

Cylinder Heads engine component fastened to the end of the cylinder block farthest from the crankshaft head gasket is filler material A cylinder head is a cast aluminum alloy or cast iron engine component fastened to the end of the cylinder block furthest from the crankshaft. A head gasket is the filler material placed between the cylinder block and the cylinder head to seal the combustion chamber. Figure 3-5.

Crankshafts convert linear motion of pistons to rotary motion crankpin journal bearing journal counterweight crankgear A crankshaft is an engine component that converts the linear (reciprocating) motion of the piston into rotary motion. Figure 3-6. The crankshaft has a crankpin journal, which is a precision ground surface that provides a rotating pivot point to attach the connecting rod to the crankshaft. The throw is the measurement from the center of the crankshaft to the center of the crankpin journal and determines the stroke of the engine. The bearing journal is a precision ground surface within which the crankshaft rotates. The counterweight is a protruding mass integrally cast into the crankshaft that partially balances the forces of a reciprocating piston and reduces the load on crankshaft bearing journals. The crankgear is a gear located on the crankshaft that is used to drive other parts of an engine. The power take-off (PTO) is an extension of the crankshaft that allows an engine to transmit power to an application.

Crankcase Houses and supports crankshaft In 4-stroke acts as oil reservoir for lubrication May have multiple parts like a sump or crankcase cover Sump is removable & acts like oil reservoir & provides access to internal parts Has bearing surface for vertical shaft engines & forms lower section of engines Horizontal shaft engines have no sump as block serves as oil reservoir Crankcase cover provides access to internal parts in crankcase & supports crankcase

Crankcase Breather Relieves crankcase pressure created by reciprocating motion of the piston during operation When piston moves towards TDC volume in crank increases resulting in lower existing pressure in crankcase When piston toward BDC volume in crankcase decreases generating higher than ambient pressure in crankcase

Crankcase Breather Acts as a check valve allowing more air to escape than can enter crankcase Maintains pressure less than atmospheric pressure (14.7 PSI at sea-level) Gases, partially spent combustion gases & other engine gases are then routed to carburetor Also serves as a oil mist collector Prevents crankcase oil from escaping whenever breather opens Required on most 4-stroke engines

Crankcase/Cylinder Block

Cylinder Blocks Cast from materials strong enough to withstand the heat & stress inside the engine during operation Must meet size & weight requirements of specific application

Cylinder Blocks Common construction Cast aluminum alloy Cast iron Lightweight & dissipates heat more rapidly than cast iron Cast iron Heavier & more expensive More resistant to wear & less prone to heat distortion Cast aluminum alloy with cast iron cylinder sleeves Combine both for maximum strength

Cylinder Heads

Cylinder Head Cast aluminum alloy or cast iron Fastened to end of cylinder block farthest from crankshaft Head gasket used between both to seal combustion chamber Made from soft metals & graphite layered together Allows for even heat distribution between block & head Some 2-stroke engines have head & block cast together called a jug Provides maximum structural integrity & eliminates potential for leaks in combustion chamber

Pistons Slides back and forth in the cylinder bore Piston pin Skirt Ring groove Piston rings Commonly made from cast iron Compression Ring Wiper Ring Oil ring A piston is a cylindrical engine component that slides back and forth in the cylinder bore by forces produced during the combustion process. The piston head is the top surface (closest to the cylinder head) of the piston and is subjected to tremendous forces and heat during normal engine operation. Figure 3-7. A piston pin bore is a through hole in the side of the piston perpendicular to piston travel that receives the piston pin. A piston pin is a hollow shaft that connects the small end of the connecting rod to the piston. The skirt of a piston is the portion of the piston closest to the crankshaft that helps align the piston as it moves in the cylinder bore. A ring groove is a recessed area located around the perimeter of the piston that is used to retain a piston ring. A piston ring is an expandable split ring used to provide a seal between the piston and the cylinder wall. Small engines commonly use a compression ring to seal the combustion chamber from any leakage; a wiper ring to further seal the combustion chamber and wipe the cylinder wall clean of excess oil; and (on four-stroke cycle engines) an oil ring that also wipes excess oil from the cylinder wall and returns it to the oil reservoir.

Pistons Generally made of cast aluminum alloy Material will always be different than engine block to prevent piston merging into block Excellent thermal conductivity Ability of material to conduct & transfer heat Aluminum expands when heated so proper clearance must be provided Insufficient clearance can cause piston to seize in bore Excessive clearance can cause loss of compression & increase piston noise

Connecting Rods and Bearings connecting rod transfers motion from piston to crankshaft bearings reduce friction, maintain clearance A connecting rod is an engine component that transfers motion from the piston to the crankshaft and must withstand sudden impact stresses from combustion and piston movement. Figure 3-9. The piston pin, or wrist pin, provides a pivot point between the piston and connecting rod. The large end of the connecting rod connects to the crankpin journal to provide a pivot point on the crankshaft. A bearing is a component used to reduce friction and to maintain clearance between stationary and rotating components of an engine. A friction bearing consists of a fixed, non-moving bearing surface, such as machined metal or pressed-in bushing, that provides a low-friction support surface for rotating or sliding surfaces. An antifriction bearing is a bearing that contains moving elements to provide a low-friction support surface for rotating or sliding surfaces. A main bearing supports and provides a low-friction bearing surface for the crankshaft. A rod bearing provides a low-friction pivot between the connecting rod and the crankshaft and the connecting rod and piston. Figure 3-12.

Crankshaft

Crankshaft Converts liner motion of piston into rotary motion Main rotating component of engine Commonly made of iron Vertical or Horizontal orientation

Crankshaft Components: Crankpin Journal Bearing Journals Precision ground surface provides pivot point to attach connecting rod to crankshaft Bearing Journals Precision ground surface which the crankshaft rotates Mates with bearing surface in cylinder block

Crankshaft Counterweights Protruding mass used to partially balance the forces of a reciprocating piston

Crankshaft Crank gear Power take-off (PTO) Gear located on crankshaft used to drive other parts of an engine Not required on all small engines Power take-off (PTO) Extension of crankshaft that allows engine to transmit power to an application

Flywheels and Valve Trains a flywheel is a disk mounted at one end of a crankshaft provides inertia for the engine maintains crankshaft rotation between combustion intervals a valve train controls the flow of gases into and out of the combustion chamber A flywheel is a cast iron, aluminum, or zinc disk that is mounted at one end of the crankshaft to provide inertia for the engine and maintain crankshaft rotation between combustion intervals. Figure 3-13. The valve train includes components required to control the flow of gases into and out of the combustion chamber.

Engine Operation intake event compression event introduces air and fuel (or just air in a diesel engine) to the combustion chamber piston moves from TCD to BDC compression event air and fuel (or just air in a diesel engine) in combustion chamber is compressed in the cylinder The intake event is an engine operation event in which the air-fuel mixture, or just air in a diesel engine, is introduced into the combustion chamber and the piston moves from TDC to BDC. Figure 3-14. The compression event is an engine operation event in which the trapped air-fuel mixture, or just air in a diesel engine, is compressed inside the cylinder. Figure 3-15.

Engine Operation ignition (combustion) event power event charge is ignited and rapidly oxidized to release energy power event expanding gases force the piston head away from the cylinder head The ignition (combustion) event is an engine operation event in which the charge is ignited and rapidly oxidized through a chemical reaction to release heat energy. Figure 3-17. The power event is an engine operation event in which hot expanding gases force the piston head away from the cylinder head. Figure 3-18.

Engine Operation exhaust event spent gases are removed from the chamber and released to atmosphere valve overlap is the point when both intake and exhaust valves are open The exhaust event is an engine operation event in which spent gases are removed from the combustion chamber and released to the atmosphere. Figure 3-19. Valve overlap is the period during engine operation when both intake and exhaust valves are open at the same time. Figure 3-20. A two-stroke cycle engine completes five events in one operating cycle: the ignition/power event, exhaust/intake event, and the compression event. Two-stroke cycle engines have fewer moving parts; smaller size and less weight; higher fuel consumption; more noise; higher operating speed and temperature; and a greater quantity of exhaust emissions.

Engine Output measured by torque and horsepower units of measurement of horsepower brake, friction, and indicated horsepower dynamometer measures torque, load, speed, and horsepower Engine output is measured by torque and horsepower. Three units of measurement of horsepower are brake, friction, and indicated horsepower. A dynamometer measures torque, load, speed, and horsepower and can be one of four types—water dynamometer, electric dynamometer, eddy current dynamometer, or prony brake dynamometer. An electric dynamometer measures brake horsepower by converting mechanical energy into electrical energy. Figure 3-32.

Engine Output factors affecting engine output displacement volumetric efficiency thermal efficiency air density Factors affecting engine output include engine displacement, volumetric efficiency, thermal efficiency, and air density.

Chapter 3 Review What is the function of a crankshaft? A crankshaft is an engine component that converts the linear (reciprocating) motion of the piston into rotary motion. What are the five events of four-stroke cycle engines? The five events of four-stroke cycle engines are intake, compression, ignition, power, and exhaust. A crankshaft is an engine component that converts the linear (reciprocating) motion of the piston into rotary motion. The five events of four-stroke cycle engines are intake, compression, ignition, power, and exhaust.