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

Chapter 14 Lesson 1 Engine Bottom End Construction

Contents (2 Topics) Cylinder block construction Piston construction

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 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 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

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