1. Modern Automotive Technology PowerPoint for by Russell Krick
Publisher The Goodheart-Willcox Co., Inc. Tinley Park, Illinois

2. Chapter 14
Engine Bottom End
Construction

3. Contents Cylinder block construction Piston construction
Piston ring construction
Piston pin construction
Connecting rod construction
Crankshaft construction
Engine bearing construction
Rear main bearing oil seal construction
Select-fit parts
Balancer shafts

4. Includes the block, crankshaft, connecting rods, and piston assemblies
Engine Bottom End
Includes the block, crankshaft, connecting rods, and piston assemblies

5. 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

6. Cylinder Block
Cylinders may be integral parts of the block or formed by pressed-in liners

7. 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

8. Cylinder Sleeves There are two basic types of sleeves: dry sleeves
wet sleeves

9. 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

10. 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

11. Sleeve Installations
Dry sleeve Wet sleeve

12. Aluminum cylinder block with pressed-in, cast iron wet sleeves
Sleeve Installations
Aluminum cylinder block with pressed-in, cast iron wet sleeves

13. 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

14. 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

15. 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

16. 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

17. 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

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

19. Piston Dimensions

20. 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

21. Cam-Ground Piston

22. 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

23. 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

24. Piston Taper

25. 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

26. This is a piston for a diesel engine having a direct injection nozzle
Piston Shape
This is a piston for a diesel engine having a direct injection nozzle

27. 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

28. Slipper Skirt Piston

29. 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

30. 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

31. Piston Ring Construction Automotive pistons normally use three rings:
two compression rings
one oil ring

32. 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

33. Compression Rings

34. Oil Rings Keep crankcase oil out of the combustion chambers
Available in two basic designs:
rail-spacer type (three piece)
one-piece type

35. Oil Rings Rail-spacer ring (most common)
One-piece ring made from cast iron

36. Piston Ring Dimensions

37. 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

38. Most piston rings use a butt joint
Piston Ring Gap
Most piston rings use a butt joint

39. Piston Ring Coatings Soft ring coatings Hard 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

40. 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

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

42. Full-Floating Piston Pin
Secured by snap rings
Free to rotate in both the rod and piston

43. Press-Fit Piston Pin
Forced tightly into the connecting rod’s small end and free to rotate in the piston pin hole

44. 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 piston’s major thrust surface
the thrust surface is the surface of the piston that is pushed tightly against the cylinder wall during the power stroke

45. The piston notch indicates the front of the piston
Piston Assembly
The piston notch indicates the front of the piston

46. This piston has a full-floating piston pin
Piston Assembly
This piston has a full-floating piston pin

47. 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

48. 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

49. Connecting Rod Features
A. Oil spurt holes
B. Drilled rod

50. 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

51. 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

52. 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

53. 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

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

55. Crankshaft Oil Passages

56. 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

57. Engine Bearing Construction
There are three basic types of engine bearings:
crankshaft main bearings
connecting rod bearings
camshaft bearings

58. Engine Bearings

59. Bearing Construction Steel is used for the body.
Alloys are plated over the backing to form the bearing surface.

60. 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

61. Bearing Crush

62. 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

63. Standard Bearing
Has the original dimensions specified for a new, unworn, or unmachined crankshaft
May have the abbreviation “STD” stamped on its back

64. 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

65. This bearing is for a journal that has been machined 0.010" undersize
Undersize Bearing
This bearing is for a journal that has been machined 0.010" undersize

66. Bearing Positioning
A. Spread
B. Lug
C. Dowel

67. 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

68. Bearing Oil Holes and Grooves

69. Main Thrust Bearing and Washers
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

70. Main Thrust Bearing and Washers

71. Washers slide into place between the crankshaft and block
Thrust Washers
Washers slide into place between the crankshaft and block

72. Rear Main Bearing Oil Seal Construction
The rear main bearing oil seal prevents oil leakage around the back of the crankshaft

73. 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

74. Two-Piece Neoprene Seal
Has a lip to trap oil and another lip that keeps dust and dirt out of the engine

75. Two-Piece Neoprene Seal
The seal fits into a groove cut into the block and rear main cap

76. One-Piece Neoprene Seal
The seal fits around the rear flange on the crankshaft

77. 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

78. 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

79. 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

80. Shafts are supported on bearings and lubricated by pressurized oil
Balancer Shafts
Shafts are supported on bearings and lubricated by pressurized oil