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

  2. Chapter 13 Engine Top End Construction

  3. Contents • Cylinder head construction • Valve train construction • Intake manifold construction • Exhaust manifold construction

  4. Engine Top End Includes the cylinder head, valve train, valve cover, and intake and exhaust manifolds

  5. Cylinder Head Construction • A bare cylinder head is a head casting with all of its parts removed • If a cylinder head becomes damaged, the technician may need to install a new bare head • All of the old, reusable parts can be removed and installed in the new head

  6. Cylinder Headand Parts

  7. Cylinder Head Construction This cast aluminum head has four-valve combustion chambers

  8. Cylinder Head Construction This cast iron head has a two-valve combustion chamber

  9. Valve Guide Construction • There are two basic types of valve guides: • integral valve guides • pressed-in valve guides

  10. Integral Valve Guide • Part of the cylinder head casting • Simply a hole machined through the cylinder head • Very common because of its low production cost

  11. Pressed-in Valve Guide • Separate sleeve forced into an oversize hole machined in the cylinder head • Made of cast iron or bronze • During repair, a worn guide can be pressed out, and a new guide quickly pressed in

  12. Valve Seat Construction • Valve seats can be integral or pressed-in • Integral valve seat • machined portion of the cylinder head casting • Pressed-in valve seat • separate part that is forced into a recess cut into the head • commonly used in aluminum heads

  13. Valve Seats and Guides

  14. Valve Seat Angle • Angle formed by the face of the seat • Most engines use a 45º angle • Some high-performance engines use seat angles of 30º

  15. Valve Seat Angle Interference angle increases sealing pressure and speeds seating

  16. Diesel Prechamber Cup • Pressed into the cylinder head of some diesel engines • Holes are machined into the deck • Prechambers are force-fit into these holes • Each prechamber forms an enclosure around the tip of an injector and glow plug

  17. Diesel Prechamber Cup Area is heated by the glow plug forbetter cold starting

  18. Stratified Charge Chamber • Fits into the cylinder head casting to form an auxiliary chamber • Uses a rich fuel mixture in the auxiliary chamber to ignite a lean mixture in the main combustion chamber

  19. Stratified Charge Chamber

  20. Valve Train Construction • The valve train controls the opening and closing of the cylinder head ports • Construction will vary with engine design • To be able to work on any type of valve train, you must understand these differences

  21. Valve Construction • Automotive engines commonly use poppet valves • Some valve stems are chrome plated to better resist wear • Grooves are cut into the valve stem tops for the keepers

  22. Valve Construction A. Polished intake valve B. Stock exhaust valve C. Hollow exhaust valve is filled with sodium for cooling

  23. Valve Face Angle • Angle formed between the valve face and valve head • Normal valve face angles are 45º and 30º

  24. Sodium-Filled Valves • Used when extra valve cooling action is needed • During operation, the sodium inside the hollow valve melts, becoming a liquid • This liquid is used to cool the valve

  25. Sodium-Filled Valves • When the valve is opened, the sodium splashes down into the head and collects heat • When the valve is closed, the sodium splashes up into the stem • Heat transfers out of the sodium and into the stem, valve guide, and engine coolant

  26. Stellite Valve Stellite coating on its face retards wear and allows the use of unleaded gasoline

  27. Valve Seal Construction • Valve seals come in two basic types: • umbrella valve seals • O-ring valve seals

  28. Umbrella Valve Seal • Shaped like a cup • Made of neoprene rubber or plastic • Slides down over the valve stem before the spring and retainer • Covers the small clearance between the valve stem and guide • Keeps oil from being drawn into the cylinder head combustion chamber

  29. Umbrella Valve Seal A. Synthetic rubber seal with plastic shedder insert B. All synthetic rubber seal C. Plastic valve seal

  30. O-ring Valve Seal • Small round seal that fits into an extra groove cut in the valve stem • Seals the gap between the retainer and valve stem • Stops oil from flowing though the retainer, and down the stem • Fits onto the valve stem after the spring and retainer

  31. O-ring Valve Seal

  32. Nylon Shedder May be used to limit the amount of oil that splashes on the valve stem

  33. Valve Spring Construction This dual coil spring is designed toincrease spring pressure

  34. Valve Spring Terminology • Spring tension • stiffness of a valve spring • service manual will give the tension in pounds or kilograms for specific compressed lengths • Spring free length • length of the spring when removed from the engine

  35. Valve Spring Shim • Very thin, accurately machined washer used to increase spring tension • When a shim is placed under a spring, the open and closed lengths of the spring are reduced • Provides a means of restoring full spring pressure without spring replacement

  36. Valve Retainers and Keepers Used to lock the valve springonto the valve

  37. Valve Spring Seat • Cup-shaped washer installed between the cylinder head and the bottom of the valve spring • Provides a pocket to hold the bottom of the valve spring

  38. Valve Rotators • Turn the valves to prevent carbon buildup and hot spots on the valve faces • May be located under or on top of the valve spring • Commonly used on exhaust valves, which are exposed to more heat than intake valves

  39. Valve Rotators This engine uses a valve rotator for each exhaust valve

  40. Valve Rotators This engine uses a valve rotatorfor each valve

  41. Valve Stem Cap • May be placed over the end of the valve stem • Helps prevent stem and rocker arm wear • Free to turn on the valve stem • Serves as a bearing that reduces friction • May be used to adjust clearance in the valve train

  42. Camshaft • Controls when the valves open and close • May be driven by gears, a chain, or a belt • There may be one or two camshafts per cylinder head

  43. Camshaft With dual overhead cam engines, there are two camshafts

  44. Cam Lobes • Precision-machined and polished surfaces on the camshaft • Variations in lobe shape control: • when each valve opens in relation to piston position • how long each valve stays open • how far each valve opens

  45. Cam Lobe

  46. Camshaft Terminology • Camshaft lift • how far the valve opens • Camshaft duration • how long the valve stays open • Valve timing • valve opening and closing in relation to the position of the pistons

  47. Camshaft Terminology • Variable valve timing • engine can alter when the valves open with engine speed • Valve overlap • time when both the intake and exhaust valves in the same cylinder are open • used to improve the movement of gases through the engine

  48. Valve Timing

  49. Dual Cam Lobes • Some camshafts are machined with dual cam lobes that have two different profile shapes • one lobe is designed for low-speed efficiency while the other lobe is designed for high-speed efficiency • ECM operates a solenoid valve that controls oil flow to shift the rocker arms from one lobe profile to the other

  50. Hollow Camshafts • Have their lobes pressed onto the shaft • To lock the lobes in place, an oversize steel ball is forced down through the center of the hollow shaft • Produces a light-weight camshaft