1. Lower End Theory and Service
Chapter 11
Lower End Theory and Service

2. Engine Lower End
The lower end of an engine is the cylinder block assembly
Includes the block, crankshaft, bearings, pistons, connecting rods, oil pump, and camshaft on OHV designs
This assembly is called a short block
A short block plus the cylinder head(s) is called a long block

3. Lower End

4. Short Block Disassembly
Remove oil pan and water pump
Remove the harmonic balancer
On OHV engines remove the timing cover
Inspect the timing chain and remove
Remove the oil pick up and oil pump
Remove lifters and keep them in order

5. Cylinder Block Disassembly
Check balance shaft clearances if necessary and remove
Rotate crankshaft so cylinder #1 is at BDC
Carefully remove all cylinder ring ridges

6. Cylinder Block Disassembly
Check bearing cap positions and mark if necessary

7. Cylinder Block Disassembly (Cont.)
Position piston at BDC for removal
Remove connecting rod cap and cover rod bolts to prevent cylinder damage
Carefully push the piston and rod with wooden handle
Be sure connecting rod does not damage the cylinder wall

9. Cylinder Block Disassembly (Cont.)
Remove the main bearing caps in the specified order
Some engines use a main bearing girdle or bedplate that houses the bearings
Carefully remove crank and store vertically
Remove the rear main oil seal and bearing inserts

10. Cylinder Block Disassembly (Cont.)
Remove the block core plugs and oil plugs to ensure thorough cleaning
Oil gallery plugs

11. Cylinder Block Houses areas where combustion takes place
Can be cast iron, aluminum or magnesium
Cast iron is very strong but heavy

12. Cylinder Block (Cont.) Most aluminum blocks use cylinder liners
Usually cannot be machined

13. Cylinder Block (Cont.)
Oil and coolant passages within the block allow for the flow of oil and coolant

14. Block Reconditioning Inspect the block for cracks and damage
Clean all threaded bores with a thread chaser
Bolt holes should be slightly chamfered

15. Block Reconditioning (Cont.)
Aluminum blocks with damaged threads may require a threaded insert – called a Helicoil

16. Block Reconditioning (Cont.)
Deck flatness is important for proper cylinder head and intake manifold fit

17. Block Reconditioning (Cont.)
Inspect cylinder walls
Wall scoring or scuffing
Most wear is at top of cylinder
Measure taper and out-of-roundness

18. Cylinder Bore Finish Surface finish must act as an oil reservoir
Rings can be damaged by a rough surface
Too smooth will not hold enough oil
Desired finish is a crisscross pattern

19. Cylinder Bore Finish (Cont.)
Deglaze if cylinder condition is within specifications
Honing removes a small amount of metal from the cylinder walls
Boring is performed when the cylinder walls are worn excessively
Oversized pistons and rings are used after boring

20. Knowledge Check
What may result if the cylinder bore finish is too smooth?
Oil may not be retained and the rings will not be lubricated as the piston moves up and down the cylinder.

21. Lifter Bores Inspect bores for cracks and excessive wear
Can be honed with a wheel cylinder hone
If the lifter bores exceed allowable wear, the block should be replaced

22. Crankshaft Saddle Alignment
Misalignment will cause the crankshaft to bend as it rotates
May be repaired by line boring
Badly warped blocks are replaced
Checked along the crankshaft saddle bore
Roundness should be checked as well

23. Crankshaft Saddle Alignment

24. Installing Core Plugs
After cleaning, the block should have new core and oil plugs installed
Coat the plug or bore lightly with a non-hardening sealer

25. Camshafts Have a cam lobe for each exhaust and intake valve
Lobe height is proportional to valve lift
May drive distributor and/or oil pump
May be iron, steel, or hollow

26. OHV Camshafts
Works with lifters, pushrods, and rocker arms to open the valves

27. Camshaft in Block

28. OHC Camshafts May be single or dual overhead camshafts
Can open valves directly or through lifters, followers, or rocker arms

29. Camshafts (Cont.) Driven at half of crankshaft speed
Cam gears are twice the size of crank gears
Each intake and exhaust valve opens and closes once per crankshaft rotation
Valve opening and closing based on the shape of the cam lobe

30. Camshaft Terminology
The shape of the cam lobe is called the cam profile
Duration is the time the valve is open
Overlap is the time both the exhaust and intake valves are open at the same time

31. Lobe Terminology

32. Camshaft Drives Belt Drive
Sprockets on the crankshaft and the camshaft are linked by a neoprene belt

33. Camshaft Drives Chain Drive
Sprockets on the crankshaft and the camshaft are linked by a continuous chain

34. Camshaft Drives Gear Drive
A gear on the crankshaft meshes directly with a gear on the camshaft

35. Camshaft Drives (Cont.)
Tensioners may be spring loaded and/or hydraulically operated
Maintains correct belt or chain tension
Have a drive side and a slack side
The tensioner is on the slack side

36. Variable Valve Timing (VVT)
VVT used on OHC and OHV engine designs
VVT systems use special camshafts and phasers

37. Knowledge Check What are the three types of camshaft drives?
Chain, belt, and gear.

38. Lifter Types - Hydraulic Lifter
Hydraulic Lifters
Uses oil to absorb the shock from the valve train movement

39. Lifter Types - Solid Lifter
Solid Lifters
Require a clearance between parts of the valve train

40. Lifter Types - Roller Lifter
Roller Lifters
Uses a roller to minimize friction

41. Camshaft Bearings
OHV engines are one piece bearings pressed into the camshaft bore
OHC can be supported by split bearings

42. Balance Shafts
Balance or silence shafts are used to reduce engine vibration
Counterweights mirror the throws of the crankshaft
Rotate opposite crankshaft rotation
Inspected and serviced as part of engine reconditioning

43. Balance Shaft (Cont.)

44. Crankshafts Made of iron or steel
Crankshaft main and rod journals are machined to very close tolerances
This allows an oil film between the journal and the bearing

46. Crankshaft Torsional Dampers
Crankshaft twists and bends under combustion forces causing harmonic vibrations
This vibration can damage the crankshaft, the engine, and/or accessories driven by the crankshaft
Two common types of torsional dampers used

47. Harmonic Balancer Also called a vibration dampener
Composed of an inner hub and outer inertia ring connected via a rubber sleeve
As the crank twists the hub applies force to the ring
The condition of the sleeve is critical

48. Harmonic Balancer

49. Fluid Damper Commonly installed by the aftermarket
Fluid filled dampers have a hub surrounded by the inertia ring
The ring is filled with a high viscosity fluid
The outer ring moves against the hub as it absorbs vibrations
This movement results in heat

50. Flywheel Helps the engine run smoother
Applies a constantly moving force to the crankshaft
Flywheel inertia helps keep the crank moving from one firing event to the next
On automatic transmissions, the flex-plate and torque converter act as a flywheel

51. Crankshaft Inspection
Check vibration damper and flywheel mounting surfaces for fretting or erosion
Look for indications of damage from previous engine failures
Check journals for signs of overheating
Check sealing surfaces for scoring or wear
Check for surface cracks

52. Journal Inspection

53. Crankshaft Reconditioning
If severely damaged, the crank should be replaced
Slight journal taper, light grooves, burnt marks, or small nicks could allow reuse
Minor journal damage may be corrected by polishing with a very fine sand paper

54. Crankshaft Straightness
Checked by supporting the crank in V-blocks at the end main bearing journals
Position a dial indicator to measure at the center main bearing journal
Turn the crank one full rotation

55. Crankshaft Bearings Called insert bearings
A split bearing with a flanged side is a thrust bearing
Many engines use bedplates instead of individual bearing caps
Tightening procedures must be followed

57. Bearing Materials Aluminum alloy Aluminum Copper and lead alloys
The most commonly used design
Aluminum
Copper and lead alloys
Steel backings coated with babbitt
Layered combination of metals

58. Bearing Spread and Crush

59. Bearing Locating Devices
Locating lugs fit into slots in the bearing bore
Oil grooves provide an adequate oil supply
Oil holes allow control of oil flow to other parts of the engine

60. Knowledge Check What is the purpose of the flanged main bearing?
To control thrust or lateral movement of the crankshaft within the block.

61. Installing Main Bearings and Crankshaft
If there is little or no wear on the journals, standard sized bearings can be used
If the journals are excessively worn, undersized bearings must be used
Undersized bearings are thicker since the crank journals are smaller

63. Installing Main Bearings and Crankshaft (Cont.)
Plastigage is used to determine main and rod bearing clearances
Insert between the bearing and journal
Torque and then loosen the bearing cap

65. Crankshaft End Play
Can be measured with feeler gauges or dial indicator
End play can be adjusted by replacing the main thrust bearing or washers
The crankshaft rear mail seal is usually installed during the final installation of the crankshaft

67. Connecting Rods Transmits the pressure on the piston to the crankshaft
Made of steel, iron, aluminum, and titanium
The small end contains the piston pin
The big end attaches to the crankshaft and is in two pieces
May supply oil to cylinder wall

69. Pistons and Piston Rings
The piston forms the lower portion of the combustion chamber
Most are made of aluminum alloys
Piston heads can be flat, concave, convex, crowned, raised, and relieved for valves

70. Pistons and Piston Rings
Below the head are the ring grooves and lands
Below the rings is the piston pin or wrist pin

71. Pistons and Piston Rings (Cont.)
The area below the pin is the piston skirt
Two types of skirts are used - the full skirt and the slipper skirt
Full skirts are used in truck and commercial engines

72. Pistons and Piston Rings (Cont.)
The top of the piston has a direction mark
Mark or arrow points to the front of the engine

73. Piston Inspection
Check for damage and cracks, or scuffing on sides of the piston
Use a piston ring expander to remove rings
Clean carbon from piston top and ring grooves
Measure ring side clearance – between the ring and the top of the ring groove
Piston diameter should be measured

74. Piston Pins Hollow steel tubes
Lubricated by oil fed through connecting rods
Stationary pins are pressed into the piston
Semi-floating pins are pressed into rod
Full-floating pins are retained by caps, plugs, snap rings, or clips

76. Piston Pins (Cont.) Inspect pin area on piston for wobble
Inspect pin for wear and pin bore in piston
Any movement up and down indicates either pin or piston needs replaced
Connecting rod may have a pin bushing

77. Piston Rings Seal the combustion chamber at the piston
Remove oil from the cylinder walls to prevent oil from entering the combustion chamber
Carry heat from the pistons to the cylinder walls to help cool the piston

78. Piston Ring Types Compression Rings Oil Control Rings
Form the seal between the piston and the cylinder wall
Most piston designs use two compression rings
Oil Control Rings
Control oil used to cool piston and lubricate cylinder walls

79. Piston Rings

80. Installing Rings Check ring end gap
Apply a light coat of oil to the rings
Install the oil control ring first, staggering the ends of the three parts
Install the second then first compression rings
Ensure the correct side is facing up
Place ring gaps per specifications

83. Knowledge Check What is the correct order for installing piston rings?
Oil rings, second compression, top compression.

84. Installing Pistons and Rods
Ensure caps and rods are a match
Insert bearings into rods and caps
Oil the cylinder walls
Coat the crankshaft journals with oil
After each piston in installed, rotate the crankshaft to check its movement

85. Checking Crankshaft Rotation

86. Inspection of Camshaft and Related Parts
Check each lobe for scoring, scuffing, fracturing, pitting, and signs of abnormal wear
Premature lobe wear is usually due to inadequate lubrication
Measure cam bearing journal diameter
Check for straightness with a dial indicator

87. Timing Components Measure timing gear backlash
Excessive backlash causes gear noise
Insufficient backlash causes gear binding

88. Lifters Inspect cam side for wear
Improper lubrication will cause excessive wear
Disassemble and clean lifters
Perform a leakdown test
Never use old lifters on a new cam or an old cam with new lifters

89. Checking Lifter Wear

90. Installation – Camshaft Bearings
Cam-in block bearings may be easier to install if crankshaft is not installed
Bearings are press fit into block using a driver
Some cam journals have different diameters
Smallest at the rear of the block and each journal progressively larger

91. Camshaft Bearing Installation

92. Installation - Camshaft
Thoroughly coat with assembly lube
Lubricate the lifters
Carefully install cam to avoid bearing damage
Install the thrust plate and cam gear
Once installed, turn the cam by hand

93. Crank and Cam Timing Timing must be set to specifications
Install the chain on the crank gear first
Never wind or pry a chain onto the gears
Check camshaft end play if required

94. Typical balance shaft timing mark arrangement

95. Balance Shafts Inspect each bearing and journal
Check oil clearances with plastigage
Apply a light coat of oil to the bearings
Align the timing marks and set the shafts into position

96. Oil Pumps Positive Displacement Pumps
The amount of oil that leaves is the amount that entered
Output volume is proportional to pump speed
Internal engine passages restrict oil flow, causing oil pressure
Oil pressure affected by oil viscosity and temperature

97. Knowledge Check
What may result from the balance shaft not being properly timed?
Engine vibration.

98. Types of Oil Pumps
Rotor-type oil pump
Gear-type oil pump