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Engine Lower End and Lubrication System Theory


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

Engine Lower End and Lubrication System Theory
  • Chapter 19

  • 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

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

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

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

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Core Plugs
  • Usually made of steel
  • Brass, rubber, stainless steel, or copper
    expandable are also used
  • Brass and stainless steel are superior in marine
  • 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

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
  • Top of cylinder receives less lubrication
  • Out-of-round wear
  • Results when piston tilts from one side to the

Cylinder Sleeves
  • Aluminum blocks
  • Usually have permanently installed iron cylinder
  • 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

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

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

Crankshaft Design
  • Journals polished bearing surfaces
  • Main bearing journals support crankshaft as it
  • 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

Crankshaft End Thrust
  • Crankshaft is pushed forward by pressure of end
  • 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

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

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

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

  • 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
  • Inserts are positioned in the bearing bore by a
    locating lug or dowel

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

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

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

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

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

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
  • Better wear characteristics

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

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

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

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

Compression Ring Design
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

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

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

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

The Lubrication System
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

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

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

Oil Pressure
  • Proper lubrication
  • Achieved by distribution of clean oil under
  • Important correct amount of bearing clearance
  • If correct bearing clearances are not maintained
    oil will not reach all areas of engine while
  • 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

High-Volume Oil Pumps
  • Output per revolution
  • Depends on diameter and thickness of rotors or
  • 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

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

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