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Engine Lower End and Lubrication System Theory

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Engine Lower End and Lubrication System Theory Chapter 19 Oil Pumps Gear on the camshaft drives the oil pump Types of oil pumps External gear Rotor or gerotor ... – PowerPoint PPT presentation

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Title: Engine Lower End and Lubrication System Theory


1
Engine Lower End and Lubrication System Theory
  • Chapter 19

2
Objectives
  • Describe the related theory of all of the parts
    that make up the lower end
  • Tell how a cylinder block is made and understand
    the functions of its parts
  • Understand how pistons are constructed and the
    reasons behind their various designs

3
Objectives (cont'd.)
  • Discuss the various types of piston rings and be
    able to make the correct choice when selecting
    rings for a rebuilt engine
  • Understand the differences in the various types
    of engine bearings
  • Describe the parts of the crankshaft and their
    functions

4
Introduction
  • Lower end consists of
  • Crankshaft assembly
  • Piston
  • Rod
  • This chapter describes
  • Lower end parts
  • Engine block
  • Lubrication system

5
Cylinder Block Construction
  • Cast using cast iron or aluminum
  • In a mold called a core
  • Core is supported around outside of core box
  • Leaves core holes in finished block
  • Molten iron poured into core box
  • Heat of casting process cooks the sand
  • Casting cools and sand breaks up
  • Casting is shaken out
  • Remaining sand washed way through core holes
  • Core holes closed off with core plugs

6
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7
Core Plugs
  • Usually made of steel
  • Brass, rubber, stainless steel, or copper
    expandable are also used
  • Brass and stainless steel are superior in marine
    environment
  • Do not rust
  • Not used in new cars because of cost
  • Not needed because coolant prevents rust
  • Also known as expansion plugs, welsh plugs,
    freeze plugs, or soft plugs

8
Cylinder Bore
  • Cylinders are bored in the block
  • Engines today little cylinder wall wear
  • Cylinder bore taper wear
  • Forms the ring ridge at the top of ring travel
  • Causes of cylinder bore taper wear
  • High pressure of piston rings against cylinder
    wall
  • Top of cylinder receives less lubrication
  • Out-of-round wear
  • Results when piston tilts from one side to the
    other

9
Cylinder Sleeves
  • Aluminum blocks
  • Usually have permanently installed iron cylinder
    sleeves
  • Sleeves
  • Replaceable cylinder bores
  • Damaged cylinders can be bored oversize
  • Accept a pressed-fit dry sleeve
  • Wet sleeves
  • Only contact block at upper and lower ends

10
Main Bearing Caps
  • Main bearing bores
  • Bored at the factory with bearing caps in place
  • Main caps are not interchangeable

11
Lifter Bores
  • Bored in the block on engines with camshafts in
    the block
  • Lifters spin in the lifter bores
  • Very little clearance to the lifters
  • Just enough to allow oil to leak below to
    lubricate camshaft lobes

12
Crankshaft Design
  • Journals polished bearing surfaces
  • Main bearing journals support crankshaft as it
    turns
  • Rod bearing journals offset from main bearing
    journal centerline
  • Counterweight opposite each rod journal balances
    offset rod journals and rod
  • Crankshafts are cast or forged
  • Forged cranks stronger, but cost more
  • Cast crankshafts larger counterweights

13
Crankshaft End Thrust
  • Crankshaft is pushed forward by pressure of end
    thrust
  • End thrust is exerted by
  • Torque converter
  • Release spring pressure of clutch
  • Thrust surfaces
  • Precision bearing surface ground on sides of
    crankshaft main bearings
  • Flanged thrust bearing
  • Fits between crankshaft thrust surfaces

14
Direction of Crankshaft Rotation
  • Most automotive engine crankshafts rotate
    counterclockwise
  • Except Hondas and Hyundais
  • Transverse mounted engines follow this standard
  • Longitudinal mounted engine
  • Turns clockwise

15
Vibration Damper
  • During combustion crankshaft twists and
    overcorrects in the other direction
  • Torsional vibration causes crankshaft to break
  • Timing chain and sprocket wear result
  • Most vibration occurs at front of the crankshaft
  • Vibration damper (i.e., harmonic balancer)
  • Dampens torsional vibration
  • Heavy outer inertia ring and inner hub separated
    by a synthetic rubber strip

16
Crankshaft Hardness
  • Some crankshafts are hardened
  • Mostly imports and heavy-duty manufacturers
  • Must be rehardened if reground
  • Crankshafts that have not been hardened will
    suffer misalignment if rehardened
  • Most crankshafts tend to work-harden with use
  • Used, polished crankshaft will have yellow tint

17
Bearings
  • Crankshaft bearings
  • Usually two-piece plain bearings with a specially
    designed surface
  • Bearing inserts
  • Made from many different materials
  • Bearing properties
  • Embeddability, conformability, and fatigue
    strength
  • Inserts are positioned in the bearing bore by a
    locating lug or dowel

18
Bearings (cont'd.)
  • Bearing spread
  • Measurement across parting face slightly larger
    than diameter of bearing bore
  • Bearing crush
  • Bearing extends above parting line of bearing
    bore half by about .0005.00015
  • Bearings come in standard sizes and undersizes
  • Undersized used when crankshaft reground
  • Cam bearings often made from seamless steel
    tubing with lining bonded to the inside

19
Connecting Rods
  • Made from forged or cast steel formed in an
    I-beam shape
  • Forged rods stronger
  • Rod caps are not interchangeable
  • Oil clearances of bearings vary greatly
  • Rod oil holes
  • Squirt oil on the cylinder wall
  • Nearly all engines are left-hand
  • When a left-hand engine has oil-spit holes they
    are to the right when the notches face forward

20
Pistons
  • Todays pistons
  • Cast or forged aluminum
  • Undergo remarkable stresses

21
Piston Head and Ring Grooves
  • Piston head (crown) is round
  • Skirt is usually oval
  • Diameter of head
  • Smaller than diameter of skirt
  • Piston ring grooves
  • Top piston ring is positioned as high as possible
    on piston
  • Holes in the oil ring groove allow excess
    cylinder wall oil to return to the crankcase

22
Heat Transfer
  • Piston crown heat
  • Transferred through piston rings to water jackets
  • Some manufacturers use different piston head
    shapes to allow compression ratio variation
  • High compression pistons can only be installed in
    one direction in the cylinder

23
Cast and Forged Pistons
  • Cast aluminum pistons most common
  • Forged pistons available for heavy-duty or
    high-performance use
  • Dense grain structure
  • 70 stronger than cast pistons
  • Hypereutectic pistons cannot withstand tensile
    loads
  • Better wear characteristics

24
Piston Skirt
  • Aluminum
  • Expands at twice the rate of cast-iron
  • To control expansion
  • Taper the piston
  • Piston skirt is cam ground
  • Struts of spring-loaded steel cast into them
  • Trunk piston
  • Full-skirt piston used on longer stroke engine
  • Slipper-skirt
  • Designed to clear the crankshaft counterweights

25
Piston Pin Offset and Piston Pins
  • Piston pin offset and height
  • Different configurations
  • Piston pins
  • Attach piston to connecting rod
  • Piston pin types
  • Pressed-fit in rod
  • Full-floating

26
Piston Rings
  • Most engines use two compression rings and one
    oil ring
  • Top ring exposed to flame of combustion during
    every power stroke
  • Piston rings
  • Seal combustion pressures
  • Help cool piston
  • Control oil consumption

27
Compression Rings
  • Forced against cylinder wall by combustion
    pressure at top and back of ring
  • Top ring controls sealing of combustion
  • Second rings captures pressure that escapes
  • Cast in groups
  • Installed on a mandrel and machined out of round
  • Low-tension rings
  • Introduced to improve fuel economy

28
Compression Ring Design
29
Compression Ring Materials and Coatings
  • Most rings made of plain cast iron
  • Cast iron rings used in re-ring jobs
  • Moly rings have groove machined on their faces
  • Chrome rings last the engine life with no wear
  • Premium ring combination
  • Moly barrel-faced top ring
  • Reverse-torsion second ring
  • Three-piece chrome oil ring

30
Compression Ring Materials and Coatings (cont'd.)
  • High-strength rings
  • Ductile iron rings withstand higher temperatures
  • Steel rings made from steel wire
  • Plasma ceramic rings
  • Five times as strong as a stock ring
  • Resist detonation damage
  • Cause less cylinder damage
  • Excellent break-in characteristics
  • Cylinder preparation same as for moly rings

31
Oil Control Rings
  • Oil rings
  • Run at a temperature of 250F
  • Oil consumption
  • Increases with engine speed
  • Vacuum during deceleration increases with
    compression ratio
  • Several oil ring designs
  • Single-piece cast types
  • Three-piece type

32
Engine Balancing
  • Engine vibration and worn parts
  • Results from a lack of engine balance
  • As engine speed doubles force from imbalance is
    multiplied by four
  • An engine can be balanced to prevent vibration
  • Material removed from heavier parts to weigh the
    same as lighter parts
  • Balance shafts
  • Silent shafts have counterweights timed to
    cancel out engines imbalance

33
The Lubrication System
34
Oil Pumps
  • Gear on the camshaft drives the oil pump
  • Types of oil pumps
  • External gear
  • Rotor or gerotor
  • Internal gear or crescent
  • Gerotor pumps
  • Smooth pumping action and less aeration of oil
  • Crankshaft-driven oil pumps
  • Turn twice as fast as camshaft-driven

35
Pressure Relief Valve
  • More oil pumped at faster speeds
  • Must have a relief valve for excessive pressure
  • Most relief valves divert excess oil back to
    inlet side of pump
  • Maximum oil pressure is controlled by tension of
    the relief valve spring
  • Too much pressure can burst the oil filter

36
Oil Pump Screen By-Pass Valve
  • Most sump screens have a by-pass valve that opens
  • Screen is plugged
  • Oil is too cold or thick to flow freely
  • Foreign material will be sucked into the pump

37
Oil Pressure
  • Proper lubrication
  • Achieved by distribution of clean oil under
    pressure
  • Important correct amount of bearing clearance
  • If correct bearing clearances are not maintained
    oil will not reach all areas of engine while
    idling
  • Excessive oil clearance near the pump results in
    insufficient oil pressure
  • Satisfactory oil pressure around 25 psi
  • Indicator lights come on when pressure drop below
    10 psi

38
High-Volume Oil Pumps
  • Output per revolution
  • Depends on diameter and thickness of rotors or
    gears
  • High-volume pumps
  • Deliver more oil per revolution
  • Provide more oil to worn engine at idle
  • May not provide any other advantages to passenger
    car engines

39
Windage Tray and Baffles
  • At high speeds revolving crankshaft creates wind
  • Causes air pockets around oil pump screen
  • Causes the pump to lose its prime
  • Windage tray
  • Prevents air pockets
  • Baffles
  • Keep oil from sloshing with car movement
  • Check for foreign material trapped under a
    windage tray or baffle

40
Dry Sump Lubrication Systems
  • More complex and cost more to produce
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