1. Chapter 3 Engine Operation
Engine Components • Four-Stroke Cycle Engines • Two-Stroke Cycle Engines • Valving Systems • Diesel Engines • Rotary Engines • Engine Output

2. 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.

3. 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.

4. 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.

5. 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.

6. 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.

7. Pistons slide back and forth in the cylinder bore piston pin skirt
ring groove
piston 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.

8. 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.

9. 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.

10. 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.

11. 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.

12. 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.

13. Valving Systems
seal the combustion chamber to control flow of air-fuel mixture into the cylinder and exhaust gases out of the cylinder
commonly two valves per system, intake and exhaust
location of valve determines type of head design
Four-stroke cycle engines control the flow of gases in the cylinder with valves, which seal the combustion chamber to control the flow of air-fuel mixture into the cylinder and exhaust gases out of the cylinder. Figure 3-23.
Small engines commonly have two valves per cylinder, an intake and an exhaust valve.
The location of valves (in the cylinder block or in the cylinder head) determines the type of head design (L-head or overhead valve) and the necessary components of the valve head. Figure 3-24.
Timing marks on the cam gear and crankgear indicate the gear teeth mesh required to prevent damage to engine components.
Valving systems on two-stroke cycle engines are less complicated and require fewer moving parts than four-stroke cycle valving systems.

14. Diesel Engines
injector is hydraulically activated by pressurized fuel delivered by the injection pump
heat in glow plug is created by resistance to current in a heating coil
Diesel engine components are similar to the components of a gasoline engine except that diesel engines have an injection pump, injector, and glow plug.
The injector is hydraulically activated by the pressurized fuel delivered from the injection pump. Figure 3-28.
Heat in the glow plug is created by resistance to current passed through a heating coil. Figure 3-29.

15. Diesel Engines five events in operation
intake
compression
ignition
power
exhaust
turbocharging uses a compressor
One operation cycle of a four-stroke cycle diesel engine includes the five events of intake, compression, ignition, power, and exhaust.
Diesel engine turbocharging uses a compressor to raise the pressure and density of the air entering the engine.
A glow plug can be used to provide an additional source of heat for preheating the air in the combustion chamber to aid starting.

16. 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.

17. 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.

18. 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.