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

Chapter 14 Engine Bottom End Construction

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

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

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

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

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 Sleeves There are two basic types of sleeves: dry sleeves wet sleeves

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

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 Dry sleeve Wet sleeve

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

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-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 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 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

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

Piston Dimensions

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

Cam-Ground Piston

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

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

Piston Taper

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

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

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

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

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 Construction Automotive pistons normally use three rings: two compression rings one oil ring

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

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

Piston Ring Dimensions

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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 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

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

Crankshaft Oil Passages

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

Engine Bearings

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

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

Bearing Crush

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

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

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

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

Bearing Positioning A. Spread B. Lug C. Dowel

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

Bearing Oil Holes and Grooves

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

Main Thrust Bearing and Washers

Washers slide into place between the crankshaft and block 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 There are several different types of seals These types include: two-piece neoprene one-piece neoprene wick or rope seal

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

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

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

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

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