Presentation on theme: "6 Engine Components. 6 Engine Components Learning Objectives Identify the basic components of a small engine and describe the function of each component."— Presentation transcript:
3Learning ObjectivesIdentify 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.
4Engine Block Keeps engine parts in alignment Cast iron or aluminum alloyConsists of two sections:Cylinder blockCrankcase
5Cylinder Block Contains cylinder bore Cylinder may be bored directly in blockAluminum cylinder blocks cast around steel sleeveCylinder head bolts to block or is cast as integral partCooling fins on block and head of air-cooled engines
6Crankcase Contains crankshaft Must withstand rotational forces of the crankshaftMay contain oil for lubricationMay be cast with engine block
7Crankshaft Major rotating part of engine Converts reciprocating motion into rotary motionTransmits engine torqueDrives camshaftSupports flywheel
8Crankshaft Cast or drop forged steel Tapered end receives flywheel Flywheel keyed to crankshaftCrankshaft throwOffset portion of shaftCounterweights offset unbalance
9Crankshaft Main Bearings Supports crankshaft in blockThree types:Sleeve or bushingRoller bearingBall bearing
14Pistons Straight line driving member Subjected to heat of combustion Adequate clearanceSeal between combustion chamber and crankcasePiston rings exert tension on cylinder wall
15Piston Construction Steel or aluminum Grooves accept piston rings Aluminum most popularGrooves accept piston ringsLands are full-diameter ridges between groovesHoles in bottom groove allow oil to flow back to sumpHole for piston pin (wrist pin)Pin boss surrounds the piston pin holePiston skirt keeps piston from tipping
17Cam Ground Piston Oval shape Thrust surfaces fit more closely Helps prevent piston slap
18Piston Head Runs hotter and expands more than skirt Smaller in diameter than skirtShape depends on applicationFour-stroke enginesFlatDomedWedgeTwo-strokeFlat with loop-scavenged engineRaised baffle or deflector with cross-scavenged engine
19Piston Rings Allow piston to compress fuel charge Prevent burning gases from leakingRide on cylinder wallsSeparated by thin film or oilRub sides of piston groovesGrooves hold rings squarely to bore
20Piston Rings Four-stroke pistons use three rings Two upper rings are compression ringsLower ring is oil control ring
21Compression Rings Provide strong seal Keeps compressed air-fuel mixture and burning gases above pistonPrevents passage between piston and cylinder wallTwists in groove during intake strokeIn tipped position during compression and exhaust strokesFlat against cylinder wall on power stroke
23Oil Control Rings Remove surplus oil from cylinder walls Light scraping actionSlotted or perforatedOil passes through holes in ring and grooveOil flows to inside of piston and into crankcase
24Piston Ring Construction Cast iron or steelPlated with long-wearing materialOutside diameter slightly larger than cylinder boreCreates ring tensionRing gapOpening between ends of ringAllows rings to expand and contract
25Piston Ring Movement Free to move inward or outward in piston grooves Floating ringsRotate around groovesInstalled with end gaps staggeredPinned ringsHeld in position by pin in ring groovePin prevents rotation of ring around grooves
26Piston Pins Secure piston to connecting rod Case-hardened steel Solid or hollowFull-floating pinRetained by snap ringsPress-fit pinFits tightly in connecting rod
27Connecting Rod Attaches piston to crankshaft Upper end accepts piston pinLower end contains bearings and fits around crankshaft journal
28Friction Bearings Used when lower end of connecting rod is split Types Rod metalBearing bronzeRemovable precision insertsLocating tabFits into slot in rod
29Antifriction Bearings Rollers or balls reduce frictionElements held together by roller cage or can be freeHardened and ground to exact sizeMust fit accurately and have clearance for expansion
30Intake and Exhaust Ports Provide means for admitting air-fuel mixture and exhausting waste productsTwo-stroke enginesPorting of cylinder wallsAlternately covered and exposed by pistonFour-stroke enginesPoppet valves open and close port opening
31Reed Valves and Rotary Valves Control fuel flow directly into crankcase of two-stroke engineReed valveOpens during compression stroke and closes before the power strokeRotary valveAttached to end of crankshaftAir-fuel charge enters crankcase when holes in valve and wear plate align
34Poppet Valves Installed in valve ports of four-stroke engines Control flow of air-fuel mixture into the cylinder and exhaust gases out of the cylinderAngled valve face closes tightly against seatValve guide aligns valve and ensures accurate raising and lowering
36Valve Spring Holds valve firmly against seat Connect to valve stem with retainer and keeperAllows valve to be opened and closes it when pressure is released from valve stem
37Camshaft Used in four-stroke engines Shaft has lobe for each valve Opens valves the right amount at the right timeHolds valve open for a specific period and allows them to close at correct instantShaft has lobe for each valveLobe lifts valve from seat when shaft rotatesRotates at half crankshaft speedCamshaft gear meshes with and is driven by crankshaft gear
38Valve Lifter Located between cam lobe and valve stem Rises and falls as camshaft rotates, opening and closing valvesMay provide means to adjust clearance
39Valve TrainTransforms crankshaft rotation into opening and closing of valvesValve train configurationsValve-in-blockOverhead valveOverhead cam
40Valve-in-Block Camshaft located in crankcase Valves located in cylinder block, directly above camshaft lobesLifters act directly on valve stems
41Overhead Valve (OHV) Camshaft installed in crankcase Valves installed in cylinder headPushrods transfer motion from valve lifters to rocker armsRocker arm pushes down on valve stem
42Overhead Cam (OHC) Both camshaft and valves in cylinder head Camshaft positioned directly above valves or offsetRocker arms used if camshaft is offsetCamshaft driven by chain or belt
43Starter Assembly Rewind starter assembly Electric starters Mounted above flywheelWhen rope is pulled, pawls engage flywheel clutch and assembly turns crankshaftWhen rope is released, pawls retract and assembly disengagesElectric starters
44Automatic Compression Release Makes hand cranking easierLifts exhaust valve during crankingReleases part of compression pressure
45Flywheel Fastened to one end of crankshaft Keeps crankshaft spinning during nonpower strokesMetal fins on flywheel force air over cylinder to cool engineContains magnets that produce electrical current for ignition system
46The two sections of the engine block are the cylinder block and the _____. crankcase
47The _____ converts the reciprocating motion of the piston into rotary motion crankshaft
48The shape of a cam-ground piston allows the _____ surfaces to fit more closely. thrust
49The _____ rings keep the air-fuel mixture and burning gases above the piston. compression
50Name the three types of friction bearings used in the big end of the connecting rod. Rod metal, bearing bronze, and removable precision inserts
51_____ bearings use rollers or balls to reduce friction between moving parts. Antifriction
52In a(n) _____ valve train, the valves are in the cylinder block and the camshaft is in the crankcase. valve-in-block
53In an overhead valve arrangement, _____ transfer motion from the valve lifters to the rocker arms. pushrods
54In an overhead cam valve train, both the camshaft and the valve assemblies are installed in the _____. cylinder head
55Glossary Antifriction bearing Automatic compression release Camshaft A bearing constructed with balls or rollers between journal and bearing surfaces to provide rolling instead of sliding friction.Automatic compression releaseMechanism on the camshaft designed to lift the exhaust valve slightly during cranking to release part of the compression pressure.CamshaftShaft containing lobes or cams that operate engine valves.
56Glossary Compression rings Connecting rod Cooling fins 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 rodLink that attaches the piston to the crankshaft.Cooling finsThin metal projections on the cylinder block that increase the surface area around the outside of the cylinder on air-cooled engines.
57Glossary Crankcase Crankcase seals Crankshaft The housing for the crankshaft and other related internal parts.Crankcase sealsSeals that prevent leakage of oil from the areas where the crankshaft and crankcase come together.CrankshaftThe major rotating part of the engine. It converts the reciprocating (back-and-forth) motion of the piston into rotary (circular) motion.
58Glossary Crankshaft throw Cylinder block Engine block The offset portion of the crankshaft measured from the centerline of the main bearing bore to the centerline of the connecting rod journal.Cylinder blockThe portion of the engine block that contains the cylinder bore.Engine blockCasting of iron or an aluminum alloy designed to keep all engine parts in alignment.
59Glossary Floating rings Flywheel 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.FlywheelA 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.
60Glossary Friction bearings Lands Oil control rings Bearing that use smooth, sliding surfaces to reduce friction between moving parts.LandsThe full-diameter ridges between the piston grooves.Oil control ringsPiston rings designed to remove surplus oil from the cylinder walls.
61Glossary Overhead cam (OHC) design Overhead valve (OHV) arrangment Valve train arrangement in which both the camshaft and the valve assemblies are located in the cylinder head.Overhead valve (OHV) arrangmentValve train arrangement in which the camshaft is installed in the crankcase and the valves are installed in the cylinder head.Pin bossThe section of the piston surrounding the piston pin hole. It is thick and often reinforced with cast-in webs.
62Glossary Pinned rings Piston 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.PistonA 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.
63Glossary Piston rings Piston skirt Poppet valve 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 skirtThe part of the piston below the rings and the bosses.Poppet valveA valve structure consisting of a circular head with an elongated stem attached in the center.
64Glossary Porting Pushrods 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.PushrodsA connecting link in an operating mechanism, such as the rod between the valve lifter and rocker arm on an overhead valve engine.
65Glossary Reed valve Rewind starter assembly Ring tension A flat, springy valve covering the ports between the carburetor and the crank chamber in a two-cycle engine.Rewind starter assemblyMechanism mounted above the flywheel on many small engines that spins, or cranks, the engine during starting.Ring tensionForce that the piston ring exerts on the cylinder wall.
66Glossary Rocker arms Rotary valves Slap Device used in overhead valve system to transfer the upward motion of the pushrod to a downward force on the valve.Rotary valvesA valve construction in which ported holes move in and out of register with each other to allow fluids or gases to enter and exit.SlapSide-to-side movement of the piston in the cylinder caused by too much clearance.
67Glossary Snap rings Sump Thrust surfaces Fasteners that are compressed and placed in grooves in the piston pin bosses. They prevent the pin from rubbing on the cylinder surface.SumpThe part of the block in a small four-stroke engine that holds and collects the lubricating oil.Thrust surfacesThe 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.
68Glossary Valve guide Valve lifter Hole machined in the engine block to align the valve and ensure accurate raising and lowering in relation to the seat.Valve lifterA rod or plunger that transfers motion from the cam and the other valve train components.
69Glossary Valve spring Valve train A spring attached to a valve to return it to the seat after it has been released from the lifting or opening operation.Valve trainAll the components that work together to transform the rotation of the crankshaft into the opening and closing of the valves.
70Glossary Valve-in-block arrangement Wrist pin 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 pinThe 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.