start Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 OBJECTIVES: After studying Chapter 26, the reader should be able to: • • • • Prepare for ASE Engine Repair (A1) certification test content area “B” (Cylinder Head and Valve Train Diagnosis and Repair) Identify combustion chamber types List the steps necessary to recondition a cylinder head Describe how to inspect and measure valve guides Continued Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 OBJECTIVES: After studying Chapter 26, the reader should be able to: • • • • Discuss valve-guide repair options Discuss various engine-valve types and materials Describe how to test valve springs Explain the purpose, function, and operation of valve rotators Continued Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 OBJECTIVES: After studying Chapter 26, the reader should be able to: • • • List the steps necessary to reface a valve Describe how to grind valve seats Discuss how to measure and correct installed height and valve-stem height Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 KEY TERMS: aluminum • arithmetic average roughness height (RA) beehive spring • bend • bronze • bronze guide liners cast iron • collet • concentric • cross-flow deflector valve stem seal • displaces • distortion fire deck • free rotators • hemiwedge • integral • interference angle kidney-shaped • microinch (in.) • nickel cobalt • O-ring valve stem seal • oversize (OS) Continued Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 KEY TERMS: pentroof • polyspherical • poppet valve • port • porting • positive rotators • positive valve stem seal • powdered metal (PM) quench area • relieving stainless steel • stellite • squish truing the valve tip • twist • umbrella valve stem seal valve face • valve guide inserts • valve rotators • valve seat • valve spring inserts (VSI) • valve spring lock (keeper) • valve spring retainer • warpage Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 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 Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 THE HEMISPHERICAL COMBUSTION CHAMBER In nonturbulent hemispherical combustion chambers, the charge is  inducted through widely slanted valves. The charge is compressed  and then ignited from a centrally located spark plug The spark plug is close to all edges of the combustion chamber.  Combustion radiates from it,  completely burning the fuel  in the shortest possible time.  Hemispherical combustion chambers are usually fully machined to form the shape, an expensive operation Figure 26–1 Hemispherical combustion chamber with a two-valve head Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 THE WEDGE COMBUSTION CHAMBER The wedge­shaped combustion chamber is designed to produce  smooth, uniform burning by controlling the rate of combustion.  In wedge­shaped chambers, the charge is inducted through valves that are side by side.  As the piston nears the top of the  compression stroke, it moves close to a low or flat portion of the head.  Figure 26–2 Cutaway of a Chevrolet V-8 cylinder head showing a wedge-shaped combustion chamber The gases are squeezed between the piston and this head surface area,  called a squish or quench area.  Continued Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 The gases squeezed from the squish area produce  turbulence within the charge. The turbulence thoroughly  mixes the air and fuel in the charge The spark plug is positioned so as to be in the highly  turbulent part of the charge. Ignition is followed by  smooth and rapid burning of the turbulent charge The combustion flame front radiates out from the spark  plug.  10 Continued Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 Checking Installed Height  When the valves and/or valve seats  have been machined, the valve projects farther than before on the  rocker arm side of the head. (The valve face is slightly recessed into  the combustion chamber side of the head.) The valve spring tension is reduced because the spring is not as  compressed as originally To restore valve spring tension, special valve spring spacers or  inserts are installed under the valve springs These shims are usually called valve spring inserts (VSI).  61 Continued Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 Valve spring inserts are generally available in three different  thicknesses: 0.015 inch (0.38 millimeter) for balancing valve spring  pressure 0.030 inch (0.75 millimeter) generally, for new springs  on cylinder heads that have had the valve seats ground  and valves refaced 0.060 inch (1.5 millimeter) necessary to bring  assembled height to specifications, especially if the  seats have been resurfaced more than one time 62 Continued Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 • To determine the exact thickness of the insert to install,  measure the valve spring height (as installed in the head).  Figure 26–39 Installed height is determined by measuring the distance from the spring seat to the bottom of the valve spring retainer Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman 63 ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 • If the installed height is greater than specifications, select the insert  (shim) that brings the installed height to within specs.  Figure 26–40 Valve spring inserts are used to restore proper installed height Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman 64 ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 VALVE STEM SEALS Leakage past valve guides is a major oil consumption problem in  any overhead valve (or overhead cam) engine A high vacuum exists in the intake port. Most engine manufacturers  use valve stem seals on both the intake and the exhaust valve The umbrella valve stem seal holds tightly to the valve stem and  moves up and down with the valve. Any oil that spills off the rocker  arms is deflected out over the valve guide. As a result, umbrella  valve stem seals are often called deflector valve stem seals The Chevrolet O­ring type of valve stem seal keeps oil from  leaking between the valve stem and valve spring retainer. The oil is  deflected over the retainer and shield. The assembly controls oil like  an umbrella­type oil seal Continued 65 Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 Positive valve stem seals hold tightly around the valve guide, and  the valve stem moves through the seal The seal wipes the excess oil from the valve stem (Figures 26–41 through 26–43) Figure 26–41 Positive valve stem seals are the most effective type because they remain stationary on the valve guide and wipe the oil from the stem as the valve moves up and down Continued Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman 66 ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 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 Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman 67 ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 INSTALLING THE VALVES The cylinder head can be assembled after cleaning with soap and  water to wash away remaining grit and metal shavings from the  valve grinding operation.  Valves are assembled in the head one at a time. Give the valve  guide and stem a liberal coating of engine oil, and install the valve  in its guide. Install umbrella or positive valve stem seals Push umbrella seals down until they touch the valve guide. Use a  plastic sleeve over the tip of the valve when installing positive seals Make sure that the positive seal is fully seated on the valve guide  and that it is square. Hold the valve against the seat as the valve  spring seat or insert, valve spring, valve seals, and retainer are  placed over the valve stem Continued 68 Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 Figure 26–44 A metal valve spring seat must be used between the valve spring and the aluminum cylinder head Many DaimlerChrysler aluminum cylinder heads use a combination valve spring seat and valve stem seal Install the valve spring seat if assembling an aluminum head.  Continued Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman 69 ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 One end of the valve spring compressor pushes on the retainer to  compress the spring. The O­ring type of valve stem seal is installed  in the lower groove.  The valve locks are installed  while the valve spring is  compressed.  To test the seal, attach the hose  from a vacuum pump to the top  of the assembled valve.  Figure 26–45 Assembling a race engine using a heavy-duty valve spring compressor A vacuum will hold if the O­ring type of valve stem seal is correctly installed Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman 70 ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 Do Not Simply Bolt On New Cylinder Heads 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? Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman 71 ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 SUMMARY The most commonly used combustion chamber types include  hemi­spherical, wedge, and pentroof Cylinder head reconditioning should start with cleaning and  repairing, if needed, followed by resurfacing of valves and,  finally, grinding of valves and seats Valve guides should be checked for wear using a ball gauge or  a dial indicator. Typical valve stem­to­guide clearance is  0.001 to 0.003 inches for intake valves and 0.002 to 0.004  inches for exhaust valves 72 Continued Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 SUMMARY (cont.) Valve guide repair options include using oversize stem  valves, replacement valve guides, valve guide inserts, and  knurling of the original valve guide Valve springs should be kept with the valve at the time of  disassembly and tested for squareness and proper spring  force Free and positive are two types of valve rotators 73 Continued Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 SUMMARY (cont.) Valve grinding should start with truing the valve tip; then the  face should be refinished. A pilot is placed into the valve guide  to position the stone or cutter correctly for resurfacing the  valve seat The installed height should be checked and corrected with  valve spring inserts if needed Valve stem height should be checked and the tip of the valve  ground if necessary 10 After a thorough cleaning, the cylinder head should be  assembled using new valve stem seals Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman 74 ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 end Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman 75 ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458