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Chapter 12

Chapter 12. Upper End Theory and Service. Cylinder Heads. Made of cast iron or aluminum Contains valves, valve seats, valve guides, springs, rocker arm supports, and the upper portion of the combustion chamber Contains coolant and oil return passages

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Chapter 12

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  1. Chapter 12 Upper End Theory and Service

  2. Cylinder Heads • Made of cast iron or aluminum • Contains valves, valve seats, valve guides, springs, rocker arm supports, and the upper portion of the combustion chamber • Contains coolant and oil return passages • Head design is one of the most influential factors in overall engine performance

  3. Cylinder Heads (Cont.)

  4. Cylinder Heads (Cont.) • Intake and exhaust ports are cast into the head • Most heads are aluminum to reduce weight • Heads can have crossflow or Siamese port

  5. Crossflow and Siamese Heads

  6. Combustion Chamber Types • Wedge Chamber • The spark plug is located at the widest part of the wedge • Hemispherical Chamber • The combustion chamber is shaped like a half circle • The spark plug is located in the center of the combustion chamber

  7. Combustion Chamber Types (Cont.) • Pentroof Combustion Chamber • Used in many modern engines • Modified hemispherical chamber design • Found mostly on engines with four valves per cylinder

  8. Wedge Combustion Chamber

  9. HemisphericalCombustion Chamber

  10. Pentroof Combustion Chamber

  11. Intake and Exhaust Valves • Commonly called poppet valves • Allow air to flow into and exhaust out of the combustion chamber • Seal the upper portion of combustion chamber • Intake valves are larger than exhaust valves

  12. Valve Construction • Most valves are hardened steel, steel alloys, or stainless steel • Intake and exhaust valves are usually made of different materials • Valves can be one or two pieces • Some exhaust valves are sodium filled • Some high performance engines use titanium valves

  13. Valve Terminology

  14. Valve Seats • May be cast into or inserted into head • Seals the valve and transfers heat

  15. Valve Guides • Support the valve and allow only up and down motion • Close clearance to valve stem • Keeps valve aligned with valve seat • Can be cast into or insert into the head

  16. Valve Guides (Cont.)

  17. Valve SpringRetainers and Oil Seals

  18. Rocker Arms and Pushrods • Change the direction of the cam’s lifting force • Pushrods link the cam to the rocker arm

  19. Cam Followers • Used on some OHC engines • Can be used to hydraulically adjust valve lash • Increases contact between cam and valve

  20. Camshaft Bearings • Most OHC cylinder heads are machined for the camshaft to ride directly on the head

  21. Knowledge Check • Technician A says the part of the valve that moves through the guide is called the valve face. Technician B says the part of the valve that moves through the guide is called the valve stem. Who is correct?

  22. Multivalve Engines • Used to improve airflow in and out of combustion chamber • Larger valves require increased spring tension • Three, four, and five valves per cylinder used • Four is most common

  23. Variable Valve Timing • VVT can be intake only, intake and exhaust, or vary lift and timing of all valves • Staged systems allow two valve timing and lift settings – Honda’s VTEC • Continuously variable systems change cam phasing

  24. VVT Phaser

  25. Fiat MultiAir • Provides variable lift and duration of intake valves • PCM controlled hydraulic solenoid controls valve opening

  26. BMW Valvetronic System • Varies intake valve lift • Combined with VANOS, provides variable lift and valve timing

  27. Cylinder Deactivation • Keeps valves closed on specific cylinders • Decreases the working displacement • OHC engines may lock and unlock the rocker arms • OHV engines deactivate lifters – Chrysler and GM displacement on demand

  28. Cylinder Head Disassembly • On some OHC engines, the rocker arms must be removed first • Remove the camshaft • Keep bearing caps and follow assemblies in order

  29. Knowledge Check • What are two advantages gained by using VVT systems in modern engines?

  30. Cylinder Head Disassembly (Cont.) • Measure spring installed height before disassembly

  31. Cylinder Head Disassembly (Cont.) • Use a socket and mallet to loosen the valve keepers • Attach and adjust the valve spring compressor • Compress the spring and remove the keepers • Remove retainer, spring(s), and seal

  32. Compressing Valve Springs

  33. Cylinder Head Inspection • Replace a head showing severe damage to valve sealing areas • Check for dents, scratches, cracks, and corrosion damage • Check intake and exhaust manifold mounting surface flatness

  34. Measure Head Warpage

  35. Cylinder Head Inspection (Cont.) • Inspect aluminum heads for porosity leaks • Check head thickness and compare to specifications • Check OHC style heads for proper cam bore alignment

  36. Valve Inspection • Check each valve face for signs of burning • Discard any valves that are burned, worn, bent, or has the plating flaking off or chipped • Look for oil buildup on the back of the valve

  37. Inspect the Stem for Wear

  38. Valves Seats • Inspect for damage, burning, cracks, and deterioration • Check for loose seats • Inspect for sunken valve seats • Seats should be replaced if the valve was broken or bent

  39. Checking for Loose Valve Seats

  40. Retainers and Keepers • Worn retainers will allow the spring to move away from the valve centerline • Uneven wear on the stem tip indicates rotators not working properly

  41. Valve Springs • Check for cracks, breaks, damage, and rust • Perform tests to determine valve spring condition • Freestanding height test • Squareness test • Open/close pressure test

  42. (A) Freestanding height (B) Closed valve spring height (C) Open valve spring height

  43. Inspection of the Valve Train • Timing Belts • Normally replaced when the engine or head is rebuilt • Ensure there are no fluid leaks that can damage the belt • Timing Chains • Measure chain for stretch • Idler Pulleys • Check for smooth operation and lubricant leakage • Tensioners • Check for smooth operation and lubricant leakage

  44. Inspection of the Valve Train (Cont.) • Gears and Sprockets • Check for cracks and tooth wear • Cam Phasers • Perform air testing of advance and retard action • Cam Followers and Lash Adjusters • Check for movement of shim

  45. Inspection of the Valve Train (Cont.) • Rocker Arms • Inspect contact points and oil feed hole • Pushrods • Check oil passage and for straightness • Camshaft and Bearings • Inspect lobe and bearing journals • Check cam straightness

  46. Knowledge Check • What are three conditions valve springs are checked for?

  47. Servicing Cylinder Heads • Cracks are common between spark plug bore and valve seat • Cracks between seats are also common

  48. Resurfacing a Cylinder Head • Resurface • Makes the sealing surface flat so the gasket seals properly • Raises the compression ratio • Squares the deck to the main bores

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