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C H A P T E R 6 Engine Components Permission granted to reproduce for educational use only.© Goodheart-Willcox Co., Inc. Identify the basic components.

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Presentation on theme: "C H A P T E R 6 Engine Components Permission granted to reproduce for educational use only.© Goodheart-Willcox Co., Inc. Identify the basic components."— Presentation transcript:

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2 C H A P T E R 6 Engine Components

3 Permission granted to reproduce for educational use only.© Goodheart-Willcox Co., Inc. Identify the basic components of a small engine and describe the function of each component. Describe engine block variations. Describe the construction and operation of the crankshaft. Explain piston design considerations and differentiate between types of piston rings. Describe connecting rod and bearing variations. Identify common valve train configurations. Learning Objectives

4 Permission granted to reproduce for educational use only.© Goodheart-Willcox Co., Inc. Engine Block Keeps engine parts in alignment Cast iron or aluminum alloy Consists of two sections: –Cylinder block –Crankcase

5 Permission granted to reproduce for educational use only.© Goodheart-Willcox Co., Inc. Cylinder Block Contains cylinder bore Cylinder may be bored directly in block Aluminum cylinder blocks cast around steel sleeve Cylinder head bolts to block or is cast as integral part Cooling fins on block and head of air-cooled enginesCooling fins

6 Permission granted to reproduce for educational use only.© Goodheart-Willcox Co., Inc. Crankcase Contains crankshaft Must withstand rotational forces of the crankshaft May contain oil for lubrication May be cast with engine block

7 Permission granted to reproduce for educational use only.© Goodheart-Willcox Co., Inc. Crankshaft Major rotating part of engine Converts reciprocating motion into rotary motion Transmits engine torque Drives camshaft Supports flywheel

8 Permission granted to reproduce for educational use only.© Goodheart-Willcox Co., Inc. Crankshaft Cast or drop forged steel Tapered end receives flywheel –Flywheel keyed to crankshaft Crankshaft throw –Offset portion of shaft Counterweights offset unbalance

9 Permission granted to reproduce for educational use only.© Goodheart-Willcox Co., Inc. Crankshaft Main Bearings Supports crankshaft in block Three types: –Sleeve or bushing –Roller bearing –Ball bearing

10 Permission granted to reproduce for educational use only.© Goodheart-Willcox Co., Inc. Crankshaft Main Bearings

11 Permission granted to reproduce for educational use only.© Goodheart-Willcox Co., Inc. Crankshaft Main Bearings

12 Permission granted to reproduce for educational use only.© Goodheart-Willcox Co., Inc. Crankcase Seals Prevent leakage Shell makes fixed contact with crankcase Knife edge rubs crankshaft Coil spring keeps sealing lip in contact with shaft

13 Permission granted to reproduce for educational use only.© Goodheart-Willcox Co., Inc. Crankcase Seal

14 Permission granted to reproduce for educational use only.© Goodheart-Willcox Co., Inc. Pistons Straight line driving member Subjected to heat of combustion –Adequate clearance Seal between combustion chamber and crankcase –Piston rings exert tension on cylinder wallPiston rings

15 Permission granted to reproduce for educational use only.© Goodheart-Willcox Co., Inc. Piston Construction Steel or aluminum –Aluminum most popular Grooves accept piston rings –Lands are full-diameter ridges between groovesLands –Holes in bottom groove allow oil to flow back to sump sump Hole for piston pin (wrist pin)wrist pin –Pin boss surrounds the piston pin holePin boss Piston skirt keeps piston from tippingPiston skirt

16 Permission granted to reproduce for educational use only.© Goodheart-Willcox Co., Inc. Piston Construction

17 Permission granted to reproduce for educational use only.© Goodheart-Willcox Co., Inc. Cam Ground Piston Oval shape Thrust surfaces fit more closelyThrust surfaces Helps prevent piston slapslap

18 Permission granted to reproduce for educational use only.© Goodheart-Willcox Co., Inc. Piston Head Runs hotter and expands more than skirt –Smaller in diameter than skirt Shape depends on application –Four-stroke engines Flat Domed Wedge –Two-stroke Flat with loop-scavenged engine Raised baffle or deflector with cross-scavenged engine

19 Permission granted to reproduce for educational use only.© Goodheart-Willcox Co., Inc. Piston Rings Allow piston to compress fuel charge Prevent burning gases from leaking Ride on cylinder walls –Separated by thin film or oil Rub sides of piston grooves –Grooves hold rings squarely to bore

20 Permission granted to reproduce for educational use only.© Goodheart-Willcox Co., Inc. Piston Rings Four-stroke pistons use three rings –Two upper rings are compression rings –Lower ring is oil control ring

21 Permission granted to reproduce for educational use only.© Goodheart-Willcox Co., Inc. Compression Rings Provide strong seal –Keeps compressed air-fuel mixture and burning gases above piston –Prevents passage between piston and cylinder wall Twists in groove during intake stroke In tipped position during compression and exhaust strokes Flat against cylinder wall on power stroke

22 Permission granted to reproduce for educational use only.© Goodheart-Willcox Co., Inc. Compression Rings

23 Permission granted to reproduce for educational use only.© Goodheart-Willcox Co., Inc. Remove surplus oil from cylinder walls –Light scraping action Slotted or perforated –Oil passes through holes in ring and groove –Oil flows to inside of piston and into crankcase Oil Control Rings

24 Permission granted to reproduce for educational use only.© Goodheart-Willcox Co., Inc. Piston Ring Construction Cast iron or steel –Plated with long-wearing material Outside diameter slightly larger than cylinder bore –Creates ring tensionring tension Ring gap –Opening between ends of ring –Allows rings to expand and contract

25 Permission granted to reproduce for educational use only.© Goodheart-Willcox Co., Inc. Piston Ring Movement Free to move inward or outward in piston grooves Floating rings –Rotate around grooves –Installed with end gaps staggered Pinned rings –Held in position by pin in ring groove –Pin prevents rotation of ring around grooves

26 Permission granted to reproduce for educational use only.© Goodheart-Willcox Co., Inc. Piston Pins Secure piston to connecting rod Case-hardened steel –Solid or hollow Full-floating pin –Retained by snap ringssnap rings Press-fit pin –Fits tightly in connecting rod

27 Permission granted to reproduce for educational use only.© Goodheart-Willcox Co., Inc. Attaches piston to crankshaft –Upper end accepts piston pin –Lower end contains bearings and fits around crankshaft journal Connecting Rod

28 Permission granted to reproduce for educational use only.© Goodheart-Willcox Co., Inc. Friction Bearings Used when lower end of connecting rod is split Types –Rod metal –Bearing bronze –Removable precision inserts Locating tab –Fits into slot in rod

29 Permission granted to reproduce for educational use only.© Goodheart-Willcox Co., Inc. Antifriction Bearings Rollers or balls reduce friction Elements held together by roller cage or can be free Hardened and ground to exact size Must fit accurately and have clearance for expansion

30 Permission granted to reproduce for educational use only.© Goodheart-Willcox Co., Inc. Intake and Exhaust Ports Provide means for admitting air-fuel mixture and exhausting waste products Two-stroke engines – Porting of cylinder wallsPorting –Alternately covered and exposed by piston Four-stroke engines –Poppet valves open and close port opening

31 Permission granted to reproduce for educational use only.© Goodheart-Willcox Co., Inc. Reed Valves and Rotary Valves Control fuel flow directly into crankcase of two- stroke engine Reed valve –Opens during compression stroke and closes before the power stroke Rotary valve –Attached to end of crankshaft –Air-fuel charge enters crankcase when holes in valve and wear plate align

32 Permission granted to reproduce for educational use only.© Goodheart-Willcox Co., Inc. Reed Valve Action

33 Permission granted to reproduce for educational use only.© Goodheart-Willcox Co., Inc. Rotary Valve Action (Evinrude Motors)

34 Permission granted to reproduce for educational use only.© Goodheart-Willcox Co., Inc. Poppet Valves Installed in valve ports of four-stroke engines Control flow of air-fuel mixture into the cylinder and exhaust gases out of the cylinder Angled valve face closes tightly against seat Valve guide aligns valve and ensures accurate raising and loweringValve guide

35 Permission granted to reproduce for educational use only.© Goodheart-Willcox Co., Inc. Poppet Valves

36 Permission granted to reproduce for educational use only.© Goodheart-Willcox Co., Inc. Valve Spring Holds valve firmly against seat Connect to valve stem with retainer and keeper Allows valve to be opened and closes it when pressure is released from valve stem

37 Permission granted to reproduce for educational use only.© Goodheart-Willcox Co., Inc. Camshaft Used in four-stroke engines –Opens valves the right amount at the right time –Holds valve open for a specific period and allows them to close at correct instant Shaft has lobe for each valve –Lobe lifts valve from seat when shaft rotates Rotates at half crankshaft speed –Camshaft gear meshes with and is driven by crankshaft gear

38 Permission granted to reproduce for educational use only.© Goodheart-Willcox Co., Inc. Located between cam lobe and valve stem Rises and falls as camshaft rotates, opening and closing valves May provide means to adjust clearance Valve Lifter

39 Permission granted to reproduce for educational use only.© Goodheart-Willcox Co., Inc. Valve Train Transforms crankshaft rotation into opening and closing of valves Valve train configurations –Valve-in-block –Overhead valve –Overhead cam

40 Permission granted to reproduce for educational use only.© Goodheart-Willcox Co., Inc. Camshaft located in crankcase Valves located in cylinder block, directly above camshaft lobes Lifters act directly on valve stems Valve-in-Block

41 Permission granted to reproduce for educational use only.© Goodheart-Willcox Co., Inc. Camshaft installed in crankcase Valves installed in cylinder head Pushrods transfer motion from valve lifters to rocker armsPushrodsrocker arms Rocker arm pushes down on valve stem Overhead Valve (OHV)

42 Permission granted to reproduce for educational use only.© Goodheart-Willcox Co., Inc. Both camshaft and valves in cylinder head Camshaft positioned directly above valves or offset –Rocker arms used if camshaft is offset Camshaft driven by chain or belt Overhead Cam (OHC)

43 Permission granted to reproduce for educational use only.© Goodheart-Willcox Co., Inc. Starter Assembly Rewind starter assembly –Mounted above flywheel –When rope is pulled, pawls engage flywheel clutch and assembly turns crankshaft –When rope is released, pawls retract and assembly disengages Electric starters

44 Permission granted to reproduce for educational use only.© Goodheart-Willcox Co., Inc. Makes hand cranking easier Lifts exhaust valve during cranking –Releases part of compression pressure Automatic Compression Release

45 Permission granted to reproduce for educational use only.© Goodheart-Willcox Co., Inc. Flywheel Fastened to one end of crankshaft Keeps crankshaft spinning during nonpower strokes Metal fins on flywheel force air over cylinder to cool engine Contains magnets that produce electrical current for ignition system

46 Permission granted to reproduce for educational use only.© Goodheart-Willcox Co., Inc. Review The two sections of the engine block are the cylinder block and the _____. crankcase

47 Permission granted to reproduce for educational use only.© Goodheart-Willcox Co., Inc. Review The _____ converts the reciprocating motion of the piston into rotary motion crankshaft

48 Permission granted to reproduce for educational use only.© Goodheart-Willcox Co., Inc. Review The shape of a cam-ground piston allows the _____ surfaces to fit more closely. thrust

49 Permission granted to reproduce for educational use only.© Goodheart-Willcox Co., Inc. Review The _____ rings keep the air-fuel mixture and burning gases above the piston. compression

50 Permission granted to reproduce for educational use only.© Goodheart-Willcox Co., Inc. Review Name the three types of friction bearings used in the big end of the connecting rod. Rod metal, bearing bronze, and removable precision inserts

51 Permission granted to reproduce for educational use only.© Goodheart-Willcox Co., Inc. Review _____ bearings use rollers or balls to reduce friction between moving parts. Antifriction

52 Permission granted to reproduce for educational use only.© Goodheart-Willcox Co., Inc. Review In a(n) _____ valve train, the valves are in the cylinder block and the camshaft is in the crankcase. valve-in-block

53 Permission granted to reproduce for educational use only.© Goodheart-Willcox Co., Inc. Review In an overhead valve arrangement, _____ transfer motion from the valve lifters to the rocker arms. pushrods

54 Permission granted to reproduce for educational use only.© Goodheart-Willcox Co., Inc. Review In an overhead cam valve train, both the camshaft and the valve assemblies are installed in the _____. cylinder head

55 Permission granted to reproduce for educational use only.© Goodheart-Willcox Co., Inc. Glossary Antifriction bearing –A bearing constructed with balls or rollers between journal and bearing surfaces to provide rolling instead of sliding friction. Automatic compression release –Mechanism on the camshaft designed to lift the exhaust valve slightly during cranking to release part of the compression pressure. Camshaft –Shaft containing lobes or cams that operate engine valves.

56 Permission granted to reproduce for educational use only.© Goodheart-Willcox Co., Inc. Glossary Compression rings –Piston rings designed to provide a strong seal, keeping the compressed air-fuel mixture and the burning gases above the piston by preventing passage between the piston and the cylinder wall. Connecting rod –Link that attaches the piston to the crankshaft. Cooling fins –Thin metal projections on the cylinder block that increase the surface area around the outside of the cylinder on air-cooled engines.

57 Permission granted to reproduce for educational use only.© Goodheart-Willcox Co., Inc. Glossary Crankcase –The housing for the crankshaft and other related internal parts. Crankcase seals –Seals that prevent leakage of oil from the areas where the crankshaft and crankcase come together. Crankshaft –The major rotating part of the engine. It converts the reciprocating (back-and-forth) motion of the piston into rotary (circular) motion.

58 Permission granted to reproduce for educational use only.© Goodheart-Willcox Co., Inc. Glossary Crankshaft throw –The offset portion of the crankshaft measured from the centerline of the main bearing bore to the centerline of the connecting rod journal. Cylinder block –The portion of the engine block that contains the cylinder bore. Engine block –Casting of iron or an aluminum alloy designed to keep all engine parts in alignment.

59 Permission granted to reproduce for educational use only.© Goodheart-Willcox Co., Inc. Glossary Floating rings –Piston rings installed with the ring end gaps staggered to avoid gap alignment and possible oil flow through the series of gaps to the combustion chamber. Flywheel –A heavy wheel fastened to one end of the crankshaft to improve the running quality of the engine. The inertia of the flywheel keeps the crankshaft spinning and smoothes engine operation.

60 Permission granted to reproduce for educational use only.© Goodheart-Willcox Co., Inc. Glossary Friction bearings –Bearing that use smooth, sliding surfaces to reduce friction between moving parts. Lands –The full-diameter ridges between the piston grooves. Oil control rings –Piston rings designed to remove surplus oil from the cylinder walls.

61 Permission granted to reproduce for educational use only.© Goodheart-Willcox Co., Inc. Glossary Overhead cam (OHC) design –Valve train arrangement in which both the camshaft and the valve assemblies are located in the cylinder head. Overhead valve (OHV) arrangment –Valve train arrangement in which the camshaft is installed in the crankcase and the valves are installed in the cylinder head. Pin boss –The section of the piston surrounding the piston pin hole. It is thick and often reinforced with cast-in webs.

62 Permission granted to reproduce for educational use only.© Goodheart-Willcox Co., Inc. Glossary Pinned rings –Piston rings that are held in position by a short pin that fits into the piston ring groove. The pin prevents rotation of the ring around the groove. Piston –A part that moves up and down in the cylinder in order to draw air-fuel mixture into the cylinder during the intake stroke, compress the mixture during the compression stroke, transfer force to the crankshaft during the combustion stroke, and force exhaust out of the cylinder during the exhaust stroke.

63 Permission granted to reproduce for educational use only.© Goodheart-Willcox Co., Inc. Glossary Piston rings –Circular rings that fit the piston grooves and exert tensions on the cylinder wall. Piston rings prevent blowby of exhaust gases into the crankcase and leakage of oil into the combustion chamber. Piston skirt –The part of the piston below the rings and the bosses. Poppet valve –A valve structure consisting of a circular head with an elongated stem attached in the center.

64 Permission granted to reproduce for educational use only.© Goodheart-Willcox Co., Inc. Glossary Porting –System that consists of two holes (ports) in the cylinder wall of some two-stroke engines. One port admits the air-fuel mixture and the other port allows exhaust gases to escape. Pushrods –A connecting link in an operating mechanism, such as the rod between the valve lifter and rocker arm on an overhead valve engine.

65 Permission granted to reproduce for educational use only.© Goodheart-Willcox Co., Inc. Glossary Reed valve –A flat, springy valve covering the ports between the carburetor and the crank chamber in a two-cycle engine. Rewind starter assembly –Mechanism mounted above the flywheel on many small engines that spins, or cranks, the engine during starting. Ring tension –Force that the piston ring exerts on the cylinder wall.

66 Permission granted to reproduce for educational use only.© Goodheart-Willcox Co., Inc. Glossary Rocker arms –Device used in overhead valve system to transfer the upward motion of the pushrod to a downward force on the valve. Rotary valves –A valve construction in which ported holes move in and out of register with each other to allow fluids or gases to enter and exit. Slap –Side-to-side movement of the piston in the cylinder caused by too much clearance.

67 Permission granted to reproduce for educational use only.© Goodheart-Willcox Co., Inc. Glossary Snap rings –Fasteners that are compressed and placed in grooves in the piston pin bosses. They prevent the pin from rubbing on the cylinder surface. Sump –The part of the block in a small four-stroke engine that holds and collects the lubricating oil. Thrust surfaces –The sides of the piston forced against the cylinder wall. These surfaces are at right angles (90°) to the centerline of the crankshaft and piston pin.

68 Permission granted to reproduce for educational use only.© Goodheart-Willcox Co., Inc. Glossary Valve guide –Hole machined in the engine block to align the valve and ensure accurate raising and lowering in relation to the seat. Valve lifter –A rod or plunger that transfers motion from the cam and the other valve train components.

69 Permission granted to reproduce for educational use only.© Goodheart-Willcox Co., Inc. Glossary Valve spring –A spring attached to a valve to return it to the seat after it has been released from the lifting or opening operation. Valve train –All the components that work together to transform the rotation of the crankshaft into the opening and closing of the valves.

70 Permission granted to reproduce for educational use only.© Goodheart-Willcox Co., Inc. Glossary Valve-in-block arrangement –Valve train arrangement in which the camshaft is located in the crankcase and the valves are located in the cylinder block, directly above the camshaft lobes. Wrist pin –The journal for the bearing in the small end of an engine connecting rod. The piston pin also passes through the piston walls, holding the piston to the connecting rod.


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