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Modern Automotive Technology by Russell Krick Publisher The Goodheart-Willcox Co., Inc. Tinley Park, Illinois PowerPoint for Chapter 14 Engine Bottom End Construction Contents (10 Topics) Cylinder block construction Piston construction Piston ring construction Piston pin construction

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Modern Automotive



Russell Krick

PublisherThe Goodheart-Willcox Co., Inc.Tinley Park, Illinois

PowerPoint for


Chapter 14

Engine Bottom End




(10 Topics)

  • 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
engine bottom end
Engine Bottom End

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


Cylinder Block


  • 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
cylinder block
Cylinder Block

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

cylinder sleeves
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
cylinder sleeves9
Cylinder Sleeves
  • There two basic types of sleeves:
    • dry sleeves
    • wet sleeves
dry sleeve
Dry Sleeve
  • Presses into a cylinder that has been bored oversize
  • Made from relatively thin material
  • Not exposed to engine coolant
  • Outer surface touches the walls of the cylinder block
wet sleeve
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
sleeve installations
Sleeve Installations

Dry sleeve Wet sleeve

sleeve installations13
Sleeve Installations

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

line boring
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
two and four bolt mains
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
crossbolted block
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
block girdle
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

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

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

cam ground piston
Cam-Ground Piston
  • Piston is machined slightly out-of-round when viewed from the top
  • Piston is 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
cam grind theory
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
  • Piston becomes round when hot
  • Cam-ground piston maintains the correct piston-to-cylinder clearance when cold and at operating temperature
piston taper
Piston Taper
  • Used to maintain the correct piston-to-cylinder clearance
  • Top of the piston is machined slightly smaller than the bottom
  • Since the piston head gets hotter than the skirt, it expands more
  • Piston is almost equal in size at the top and bottom at operating temperature
piston shape
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
piston shape27
Piston Shape

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

slipper skirt
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
slipper skirt piston
Slipper Skirt Piston

Valve reliefs providepiston-to-valve clearance

variable compression piston
Variable Compression Piston
  • Two-piece design controlled by engine oil pressure
  • 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
variable compression piston31
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

Piston Ring


  • Automotive pistons normally use three rings:
    • two compression rings
    • one oil ring
compression rings
Compression Rings
  • Prevent pressure leakage into the crankcase
  • Wipe some of the oil from the cylinder walls
  • Usually made of cast iron
  • Outer layer of chrome or other metal may be used to increase wear resistance
oil rings
Oil Rings
  • Keep crankcase oil out of the combustion chambers
  • Available in two basic designs:
    • rail-spacer type (three piece)
    • one-piece type
oil rings36
Oil Rings
  • Three-piece ring (most common)
  • One-piece ring made from cast iron
piston ring gap
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
piston ring gap39
Piston Ring Gap

Most piston rings use a butt joint

piston ring coatings
Piston Ring Coatings
  • Soft ring coatings
    • porous metal, usually iron, help the ring wear in quickly
    • 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

Piston Pin Construction

  • Piston pins are normally made of case-hardened steel that increases the wear resistance of the piston pin
  • Hollow piston pin is machined and polished to a very precise finish
piston pins
Piston Pins
  • Piston pins are held in the piston by one of two means:
    • snap rings (full-floating piston pin)
    • press-fit
full floating piston pin
Full-floating Piston Pin

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

press fit piston pin
Press-fit Piston Pin

Forced tightly into the connectingrod’s small end. Free to rotate inthe piston pin hole

piston pin offset
Piston Pin Offset
  • Locates the piston pin hole slightly to one side of the piston centerline
  • Helps quiet the piston during use
  • Pin hole is moved toward the piston’s major thrust surface
    • surface of the piston that is pushed tightly against the cylinder wall during the power stroke
piston assembly
Piston Assembly

Piston notch indicates the front of the piston

piston assembly47
Piston Assembly

This piston has afull-floating piston pin


Connecting Rod


  • Most connecting rods are made of steel
  • Connecting rods normally have an I-beam shape for a high strength-to-weight ratio
connecting rod features
Connecting Rod Features
  • Oil spurt holes
    • provide added lubrication for the piston pin, cam lobes, cylinder walls, and other parts
  • Drilled rod
    • allows oil to enter the clearance between the pin and bushing
connecting rod features50
Connecting Rod Features

A. Oil spurtholes

B. Drilled rod

connecting rod numbers
Connecting Rod Numbers

Ensure proper location of each connecting rod, and proper match of connecting rod and cap

broken surface rod
Broken-surface Rod
  • 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
powdered metal forging
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
machined block forging
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
    • small blip of rough metal produced when the two halves of the forge come together to “smash” the metal into shape

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
crankshaft oil flow
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

Engine Bearing


  • There are three basic types of engine bearings:
    • crankshaft main bearings
    • connecting rod bearings
    • camshaft bearings
bearing construction
Bearing Construction

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

bearing crush
Bearing Crush
  • Used to help prevent the bearing from spinning inside its bore
  • Bearing is made slightly larger in diameter than the bearing bore
  • When the rod or main cap is tightened, the bearing ends press against each other, locking them in place
bearing spread
Bearing Spread
  • Used on split-type engine bearings to hold the bearing in place during assembly
  • Distance across the parting line of the bearing is wider than the bearing bore
    • causes the bearing insert to stick in its bore when pushed into place
standard bearing
Standard Bearing
  • Has the original dimensions for a new, unworn, or unmachined crankshaft
  • May have the abbreviation “STD” stamped on its back
undersize bearing
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
undersize bearing66
Undersize Bearing

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

bearing positioning
Bearing Positioning

A. Spread

B. Lug

C. Dowel

bearing oil holes and grooves
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
main thrust bearing and washers
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
thrust washers
Thrust Washers

Washers slide into place between the crankshaft and block


Rear Main Bearing

Oil Seal Construction

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

rear main bearing oil seal
Rear Main Bearing Oil Seal
  • There are several different types of seal
  • These types include:
    • two-piece neoprene
    • one-piece neoprene
    • wick or rope seal
two piece neoprene seal
Two-PieceNeoprene Seal

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

two piece neoprene seal76
Two-PieceNeoprene Seal

Seal fits into a groove cut into the block and rear main cap

one piece neoprene seal
One-PieceNeoprene Seal

Seal fits around the rear flangeon the crankshaft

wick rear oil seal
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

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

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
balancer shafts
Balancer Shafts

Shafts are supported on bearings and lubricated by pressurized oil