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: This chapter describes:
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

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 Sleeves
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 Bearing inserts Bearing properties
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 Bearing crush
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 Today’s 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 Trunk piston Slipper-skirt
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 Oil consumption Several oil ring designs
Run at a temperature of 250°F
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 Gerotor pumps
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 High-volume pumps
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