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

  2. Chapter 14 Engine Bottom End Construction

  3. Contents (10 Topics) • Cylinder block construction • Piston construction • Piston ring construction • Piston pin construction • Connecting rod construction

  4. Contents • Crankshaft construction • Engine bearing construction • Rear main bearing oil seal construction • Select-fit parts • Balancer shafts

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

  6. 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

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

  8. 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

  9. Cylinder Sleeves • There two basic types of sleeves: • dry sleeves • wet sleeves

  10. 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

  11. 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

  12. Sleeve Installations Dry sleeve Wet sleeve

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

  14. 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

  15. 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

  16. 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

  17. 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

  18. 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

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

  20. Piston Dimensions

  21. 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

  22. Cam-Ground Piston

  23. 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

  24. 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

  25. Piston Taper

  26. 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

  27. Piston Shape This is a piston for a diesel engine having a direct injection nozzle

  28. 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

  29. Slipper Skirt Piston Valve reliefs providepiston-to-valve clearance

  30. 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

  31. 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

  32. Piston Ring Construction • Automotive pistons normally use three rings: • two compression rings • one oil ring

  33. 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

  34. Compression Rings

  35. Oil Rings • Keep crankcase oil out of the combustion chambers • Available in two basic designs: • rail-spacer type (three piece) • one-piece type

  36. Oil Rings • Three-piece ring (most common) • One-piece ring made from cast iron

  37. Piston Ring Dimensions

  38. 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

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

  40. 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

  41. 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

  42. Piston Pins • Piston pins are held in the piston by one of two means: • snap rings (full-floating piston pin) • press-fit

  43. Full-floating Piston Pin Secured by snap rings. Free to rotate in both the rod and piston

  44. Press-fit Piston Pin Forced tightly into the connectingrod’s small end. Free to rotate inthe piston pin hole

  45. 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

  46. Piston Assembly Piston notch indicates the front of the piston

  47. Piston Assembly This piston has afull-floating piston pin

  48. 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

  49. 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

  50. Connecting Rod Features A. Oil spurtholes B. Drilled rod