Modern Automotive

1
PowerPoint for
Modern Automotive Technology
by Russell Krick
2
Chapter 14
Engine Bottom End Construction
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Contents
(10 Topics)

• Cylinder block construction
• Piston construction
• Piston ring construction
• Piston pin construction
• Connecting rod construction

4
Contents

• Crankshaft construction
• Engine bearing construction
• Rear main bearing oil seal construction
• Select-fit parts
• Balancer shafts

5
Engine Bottom End

• Includes the block, crankshaft, connecting rods,
  and piston assemblies

6
Cylinder Block Construction

• Engine cylinder blocks are normally made of cast
  iron or aluminum
• Cast iron is very heavy and strong
• Aluminum is relatively light and dissipates heat
  well

7
Cylinder Block

• Cylinders may be integral parts of the block or
  formed by pressed-in liners

8
Cylinder Sleeves

• Metal, pipe-shaped inserts that fit into the
  cylinder block
• act as cylinder walls
• Cast iron sleeves are commonly used in aluminum
  cylinder blocks
• Sleeves can also be installed to repair badly
  damaged cylinder walls in cast iron blocks

9
Cylinder Sleeves

• There two basic types of sleeves
• dry sleeves
• wet sleeves

10
Dry Sleeve

• Presses into a cylinder that has been bored
  oversize
• Made from relatively thin material
• Not exposed to engine coolant
• The outer surface touches the walls of the
  cylinder block

11
Wet Sleeve

• Exposed to the engine coolant
• Thicker construction than a dry sleeve
• Designed to withstand combustion pressure and
  heat without the added support of the cylinder
  block

12
Sleeve Installations

• Dry sleeve Wet sleeve

13
Sleeve Installations

• Aluminum cylinder block with pressed-in, cast
  iron wet sleeves

14
Line Boring

• Machining operation that cuts a series of holes
  through the block for the crankshaft or camshaft
  bearings
• Holes must be in perfect alignment for the
  crankshaft or camshaft to turn freely

15
Two- and Four-Bolt Mains

• Two-bolt main block
• uses two cap screws to secure each main bearing
  cap to the block
• Four-bolt main block
• uses four cap screws to hold each main cap
• used on high-performance engines
• with extra bolts, the block can withstand more
  crankshaft downward pressure

16
Crossbolted Block

• Has extra cap screws going in through the sides
  of the block and main caps for added strength
• Often used on high-performance engines

17
Block Girdle

• Also called a main bearing bedplate
• Large one-piece cap that fits over the entire
  bottom of the block
• All the main caps are formed as one piece to
  increase strength and block stiffness

18
Piston Construction

• Pistons are normally cast or forged from an
  aluminum alloy
• Cast pistons
• relatively soft, used in slow-speed,
  low-performance engines
• Forged pistons
• used in fuel-injected, turbocharged, and diesel
  engines

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Piston

• This piston is for a diesel engine and has a
  groove that allows an oil spray to help cool the
  piston

20
Piston Dimensions
21
Cam-Ground Piston

• Slightly out-of-round when viewed from the top
• Machined a few thousandths of an inch larger in
  diameter perpendicular to the piston pin
  centerline
• compensates for different rates of expansion due
  to differences in metal wall thickness

22
Cam-Ground Piston
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Cam-Grind Theory

• As the piston is heated, the thicker area around
  the pin boss causes the piston to expand more
  parallel to the piston pin
• The piston becomes round when hot
• A cam-ground piston maintains the correct
  piston-to-cylinder clearance when cold and at
  operating temperature

24
Piston Taper

• Used to maintain the correct piston-to-cylinder
  clearance
• The top of the piston is machined slightly
  smaller than the bottom
• Since the piston head gets hotter than the skirt,
  it expands more
• The piston is almost equal in size at the top and
  bottom at operating temperature

25
Piston Taper
26
Piston Shape

• Refers to the contour of the piston head
• Piston head is shaped to match and work with the
  shape of the combustion chamber
• Piston may have a flat top or a domed head

27
Piston Shape

• This is a piston for a diesel engine having a
  direct injection nozzle

28
Slipper Skirt

• Produced when the portions of the piston skirt
  below the piston pin ends are removed
• Provides clearance between the piston and the
  crankshaft counterweights
• Piston can slide farther down in the cylinder
  without hitting the crankshaft

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Slipper Skirt Piston
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Variable Compression Piston

• A two-piece design controlled by engine oil
  pressure
• The piston head fits over and slides on the main
  body of the piston
• Engine oil pressure is fed between the two halves
  to form a hydraulic cushion

31
Variable Compression Piston

• With normal driving, oil pressure extends the top
  of the piston for maximum compression ratio and
  power
• When engine speed increases, combustion pressure
  pushes the head down to lower the compression
  ratio
• prevents engine knocking and pinging

32
Piston Ring Construction

• Automotive pistons normally use three rings
• two compression rings
• one oil ring

33
Compression Rings

• Prevent pressure leakage into the crankcase
• Wipe some of the oil from the cylinder walls
• Usually made of cast iron
• An outer layer of chrome or other metal may be
  used to increase wear resistance

34
Compression Rings
35
Oil Rings

• Keep crankcase oil out of the combustion chambers
• Available in two basic designs
• rail-spacer type (three piece)
• one-piece type

36
Oil Rings

• Rail-spacer ring (most common)
• One-piece ring made from cast iron

37
Piston Ring Dimensions
38
Piston Ring Gap

• Distance between the ends of the ring when
  installed in the cylinder
• Allows the ring to be installed on the piston and
  to spring outward in its cylinder
• Allows the ring to conform to any variation in
  the cylinder diameter due to wear

39
Piston Ring Gap

• Most piston rings use a butt joint

40
Piston Ring Coatings

• Soft ring coatings
• porous metal, such as iron
• help the ring wear in quickly
• the outer surface will wear away rapidly so the
  ring conforms to the shape of the cylinder
• Hard ring coatings
• chrome or moly
• increase ring life and reduce friction
• used in new or freshly machined cylinders

41
Piston Pin Construction

• Piston pins are normally made of case-hardened
  steel, which increases the wear resistance
• A hollow piston pin is machined and polished to a
  very precise finish

42
Piston Pins

• Piston pins are held in the piston by one of two
  means
• snap rings (full-floating piston pin)
• press-fit

43
Full-Floating Piston Pin

• Secured by snap rings
• Free to rotate in both the rod and piston

44
Press-Fit Piston Pin

• Forced tightly into the connectingrods small
  end and free to rotate inthe piston pin hole

45
Piston Pin Offset

• Locates the piston pin hole slightly to one side
  of the piston centerline
• Helps quiet the piston during use
• The piston pin hole is moved toward the pistons
  major thrust surface
• the thrust surface is the surface of the piston
  that is pushed tightly against the cylinder wall
  during the power stroke

46
Piston Assembly

• The piston notch indicates the front of the piston

47
Piston Assembly

• This piston has afull-floating piston pin

48
Connecting Rod Construction

• Most connecting rods are made of steel
• Connecting rods normally have an I-beam
  shape for a high strength-to-weight ratio

49
Connecting Rod Features

• Oil spurt holes
• provide added lubrication for the piston pin,
  cylinder walls, and other parts
• Drilled rod
• allows oil to enter the clearance between the pin
  and bushing

50
Connecting Rod Features

• A. Oil spurtholes

B. Drilled rod
51
Connecting Rod Numbers

• Ensure that each connecting rod is in the proper
  location and that the rod cap is installed on the
  corresponding rod body correctly

52
Broken-Surface Rod

• The rod is scribed and broken off when
  manufactured
• Produces a rough, irregular mating surface
  between the rod and cap
• Done to help lock the rod and cap into alignment

53
Powdered Metal Forging

• Forms the rough shape of the part out of metal
  powder before final shaping in a powerful forge
• Helps control the shape and weight while reducing
  machining

54
Machined Block Forging

• Involves initial turning in a lathe to bring the
  blank of metal to size before forming it in a
  drop forge
• Helps eliminate flashing
• flashing is a small blip of rough metal produced
  when the two halves of the forge come together to
  smash the metal into shape

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Crankshaft Construction

• Engine crankshafts are usually made of cast iron
  or forged steel
• Forged steel crankshafts are needed for
  heavy-duty applications
• turbocharged or diesel engines

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Crankshaft Oil Passages
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Crankshaft Oil Flow

• Oil enters the crankshaft at the main bearings
  and passes through holes in the main bearing
  journals
• Oil then flows through passages in the crankshaft
  and out to the connecting rod bearings

58
Engine Bearing Construction

• There are three basic types of engine bearings
• crankshaft main bearings
• connecting rod bearings
• camshaft bearings

59
Engine Bearings
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Bearing Construction

• Steel is used for the body
• Alloys are plated over the backing to form the
  bearing surface

61
Bearing Crush

• Used to help prevent the bearing from spinning
  inside its bore
• The bearing is made slightly larger than the
  bearing bore
• When the rod or main cap is tightened, the
  bearing ends press against each other, locking
  the bearing in place

62
Bearing Crush
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Bearing Spread

• Used on split-type engine bearings to hold the
  bearing in place during assembly
• The distance across the parting line of the
  bearing is wider than the bearing bore
• bearing spread causes the bearing insert to stick
  in its bore when pushed into place

64
Standard Bearing

• Has the original dimensions specified for a new,
  unworn, or unmachined crankshaft
• May have the abbreviation STD stamped on its
  back

65
Undersize Bearing

• Used on a crankshaft journal that has been
  machined to a smaller diameter
• Available in undersizes of 0.010", 0.020", 0.030"
  and sometimes 0.040"
• Undersize is normally stamped on the back of the
  bearing

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Undersize Bearing

• This bearing is for a journal that has been
  machined 0.010" undersize

67
Bearing Positioning

• A. Spread

B. Lug
C. Dowel
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Bearing Oil Holes and Grooves

• Holes allow oil to flow through the block and
  into the clearance between the bearing and the
  journal
• Grooves provide a channel so oil can completely
  encircle the bearing before flowing over and out
  of it

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Bearing Oil Holes and Grooves
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Main Thrust Bearing and Washers

• Main thrust bearing
• limits crankshaft end play
• thrust flanges are formed on the main bearing
  sides, almost touching the thrust surfaces
  machined on the crankshaft
• Thrust washers
• used instead of a thrust bearing to limit crank
  end play

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Main Thrust Bearingand Washers
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Thrust Washers

• Washers slide into place between the crankshaft
  and block

73
Rear Main Bearing Oil Seal Construction

• The rear main bearing oil seal prevents oil
  leakage around the back of the crankshaft

74
Rear Main Bearing Oil Seal

• There are several different types of seals
• These types include
• two-piece neoprene
• one-piece neoprene
• wick or rope seal

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Two-PieceNeoprene Seal

• Has a lip to trap oil and another lip that keeps
  dust and dirt out of the engine

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Two-PieceNeoprene Seal

• The seal fits into a groove cut into the block
  and rear main cap

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One-PieceNeoprene Seal

• The seal fits around the rear flangeon the
  crankshaft

78
Wick Rear Oil Seal

• Woven rope filled with graphite
• One piece of the rope seal fits into a groove in
  the block
• Another piece fits in a groove in the main cap
• Not as common on modern vehicles as one- and
  two-piece neoprene seals

79
Select-Fit Parts

• Parts that are selected and installed in a
  certain position to improve the fit or clearance
  between parts
• pistons are commonly selected to fit precisely
  into their cylinders
• Because of select-fit parts, it is important that
  you reinstall parts in their original locations

80
Balancer Shafts

• Used in some engines to cancel the vibrating
  forces produced by crankshaft, piston, and rod
  movement
• Usually found on 4- and 6-cylinder engines
• Usually, a chain is used to turn the shafts at
  twice crankshaft rpm

81
Balancer Shafts

• Shafts are supported on bearings and lubricated
  by pressurized oil