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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

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Chapter 14

Engine Bottom End


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(10 Topics)

  • Cylinder block construction

  • Piston construction

  • Piston ring construction

  • Piston pin construction

  • Connecting rod construction

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  • Crankshaft construction

  • Engine bearing construction

  • Rear main bearing oil seal construction

  • Select-fit parts

  • Balancer shafts

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Engine Bottom End

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

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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

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Cylinder Block

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

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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

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Cylinder Sleeves

  • There two basic types of sleeves:

    • dry sleeves

    • wet sleeves

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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

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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

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Sleeve Installations

Dry sleeveWet sleeve

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Sleeve Installations

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

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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

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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

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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

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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

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

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Piston Dimensions

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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

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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

  • Piston becomes round when hot

  • Cam-ground piston maintains the correct piston-to-cylinder clearance when cold and at operating temperature

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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

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Piston Taper

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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

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Piston Shape

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

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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

Valve reliefs providepiston-to-valve clearance

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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

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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

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Piston Ring


  • Automotive pistons normally use three rings:

    • two compression rings

    • one oil ring

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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

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Compression Rings

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Oil Rings

  • Keep crankcase oil out of the combustion chambers

  • Available in two basic designs:

    • rail-spacer type (three piece)

    • one-piece type

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Oil Rings

  • Three-piece ring (most common)

  • One-piece ring made from cast iron

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Piston Ring Dimensions

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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

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Piston Ring Gap

Most piston rings use a butt joint

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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

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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

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Piston Pins

  • Piston pins are held in the piston by one of two means:

    • snap rings (full-floating piston pin)

    • press-fit

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Full-floating Piston Pin

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

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Press-fit Piston Pin

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

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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

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Piston Assembly

Piston notch indicates the front of the piston

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Piston Assembly

This piston has afull-floating piston pin

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Connecting Rod


  • Most connecting rods are made of steel

  • Connecting rods normally have an I-beam shape for a high strength-to-weight ratio

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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

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Connecting Rod Features

A. Oil spurtholes

B. Drilled rod

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Connecting Rod Numbers

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

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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

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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

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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

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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

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Engine Bearing


  • There are three basic types of engine bearings:

    • crankshaft main bearings

    • connecting rod bearings

    • camshaft bearings

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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

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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

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Bearing Crush

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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

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Standard Bearing

  • Has the original dimensions for a new, unworn, or unmachined crankshaft

  • May have the abbreviation “STD” stamped on its back

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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

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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

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Rear Main Bearing

Oil Seal Construction

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

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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

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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

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

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One-PieceNeoprene Seal

Seal fits around the rear flangeon the crankshaft

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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

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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

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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

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Balancer Shafts

Shafts are supported on bearings and lubricated by pressurized oil

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