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7. Cylinder heads are the most frequently serviced engine components. The highest temperatures and pressures in the entire engine are located in the combustion chamber. The valves in the cylinder head(s) must open and close thousands of times each time the engine is operated. Combustion chambers of modern automotive overhead-valve engines are of two basic types: the nonturbulent hemispherical chamber and the turbulent wedge chamber.

19. Figure 26–10 A valve spring compressor is used to compress the valve spring before removing the keepers (locks). When disassembling or reassembling a cylinder head, always wear safety glasses. Valve springs, when compressed, represent stored energy. Valve keepers can be sent flying through the air by the force of an expanding valve spring, which could put out an eye or cause other physical harm. Boing! Continued

20. CAUTION: All valve train components that are to be reused must be kept together. As wear occurs, parts become worn together. Pushrods can be labeled and kept in order if they are stuck through a cardboard box, as shown here. Be sure to keep the top part of the pushrod at the top. Intake and exhaust valve springs are different and must be kept with the correct valve. Figure 26–11 Sticking pushrods through a cardboard box is a method used to keep the valve train parts in proper order.

30. Figure 26–18 A small hole gauge and a micrometer are being used to measure the valve guide. The guide should be measured in three places: at the top, middle, and bottom. Continued

31. Figure 26–19 The diameter of the valve stem is being measured using a micrometer. The difference between the inside diameter of the valve guide and the diameter of the valve stem is the valve guide-to-valve stem clearance. Continued

32. Figure 26–20 Measuring valve guide-to-stem clearance with a dial indicator while rocking the stem in the direction of normal thrust. The reading on the dial indicator should be compared to spec because it does not give the guide-to-stem clearance directly. The valve is usually limited to its maximum operating lift. Continued

37. Figure 26–22 This cylinder head has been restored to service by replacing the original valve guides with bronze valve guides.

41. Figure 26–24 Identification and relationship of valve components. Note the different valve locks (keepers) used on the exhaust valve as compared to the intake valve. The oil seals shown are also called umbrella-type valve stem seals. Continued

42. Serious valve damage can occur if cold air reaches hot exhaust valves soon after the engine is turned off. An engine equipped with exhaust headers and/or straight-through mufflers can allow cold air a direct path to the hot exhaust valve. The exhaust valve can warp and/or crack as a result of rapid cooling. This can easily occur during cold, windy weather when the wind can blow cold out-side air directly up the exhaust system. Using reverse-flow mufflers with tailpipes and a catalytic converter reduces the possibility of this occurring. Hot Engine + Cold Weather = Trouble

50. Figure 26–29 Type of valve rotator operation. Ball-type operation is on the left and spring-type operation is on the right.

53. Figure 26–33 Grinding a 60° angle removes metal from the bottom to raise and narrow the seat. Figure 26–34 The seat must contact evenly around the valve face. For good service life, both margin and overhang should be at least 1/32 inch (0.8 mm).

55. NOTE: Some experts recommend using lapping compound on the valve seat and valve face and rotating the valve to improve the valve seating. Figure 26–35 After the valve face and the valve seat are ground (reconditioned), lapping compound is used to smooth the contact area between the two mating surfaces. Notice the contact is toward the top of the face. For maximum life, the contact should be in the middle of the face.

67. Figure 26–42 An assortment of shapes, colors, and materials of positive valve stem seals. Figure 26–43 The positive valve stem seal is installed on the valve.

71. New, assembled cylinder heads, whether aluminum or cast iron, are a popular engine build-up option. However, experience has shown that metal shavings and casting sand are often found inside the passages. Before bolting on these “ready-to-install” heads, disassemble them and clean all passages. Often machine shavings are found under the valves. If this debris were to get into the engine, the result would be extreme wear or damage to the pistons, rings, block, and bearings. This cleaning may take several hours, but how much is your engine worth? Do Not Simply Bolt On New Cylinder Heads

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