13 Engine Top End Construction Chapter

Permission granted to reproduce for educational use only.© Goodheart-Willcox Co., Inc. Objectives After studying this chapter, you will be able to: Describe the design and construction of an engine cylinder head. Explain umbrella and O-ring valve seals. Explain the purpose of valve spring shims, rotators, stem caps, and spring shields. Describe the construction and operation of a camshaft.

Permission granted to reproduce for educational use only.© Goodheart-Willcox Co., Inc. Objectives Explain hydraulic and mechanical lifters. Describe different types of rocker arm assemblies. Explain the construction and design of intake and exhaust manifolds. Describe safety practices used when working on engine top end components. Answer ASE certification test questions that require a knowledge of engine top end construction.

Permission granted to reproduce for educational use only.© Goodheart-Willcox Co., Inc. Engine Top End Cylinder head assembly Valve train Valve cover Intake manifold Exhaust manifold

Permission granted to reproduce for educational use only.© Goodheart-Willcox Co., Inc. Cylinder Head Construction Bare cylinder head –Complex metal casting with all of its parts removed Valves Keepers Retainers Springs Seals Rocker arms

Permission granted to reproduce for educational use only.© Goodheart-Willcox Co., Inc. Valve Guide Construction Integral valve guide –Hole machined through cylinder head Pressed-in valve guide –Separate sleeve forced into hole machined in cylinder head

Permission granted to reproduce for educational use only.© Goodheart-Willcox Co., Inc. Valve Seat Construction Integral valve seat –Machined portion of cylinder head casting Pressed-in valve seat or seat insert –Separate part forced into recess cut into head

Permission granted to reproduce for educational use only.© Goodheart-Willcox Co., Inc. Valve and Seat angles Valve seat angle –Formed by face of seat Interference angle –1/2°–1° difference between valve seat face angle and angle of valve face (TRW)

Permission granted to reproduce for educational use only.© Goodheart-Willcox Co., Inc. Prechamber Cup Pressed into cylinder head of some diesel engines Forms enclosure around tip of injector and glow plug Heated by glow plug for better cold starting ( General Motors)

Permission granted to reproduce for educational use only.© Goodheart-Willcox Co., Inc. Stratified Charge Chamber Fits into cylinder head casting –Found in gasoline engines –Uses rich fuel mixture in auxiliary chamber Ignite lean mixture in main combustion chamber

Permission granted to reproduce for educational use only.© Goodheart-Willcox Co., Inc. Valve Train Construction Valve train –Controls opening and closing of cylinder head ports

Permission granted to reproduce for educational use only.© Goodheart-Willcox Co., Inc. Valve Construction Poppet or mushroom valves –Valve’s shape and action –Intake valve normally larger than exhaust valve

Permission granted to reproduce for educational use only.© Goodheart-Willcox Co., Inc. Valve Construction (Cont.) Valve face angle –Formed between valve face and valve head Normal valve face angles are 45° and 30°

Permission granted to reproduce for educational use only.© Goodheart-Willcox Co., Inc. Valve Seal Construction Umbrella –Shaped like cup Neoprene rubber or plastic O-ring –Small round seal Fits into extra groove cut in valve stem Soft synthetic rubber Stretched over valve stem

Permission granted to reproduce for educational use only.© Goodheart-Willcox Co., Inc. Valve Seal Construction (Cont.) Valve spring shield –Used with O-ring valve seal –Nylon shedder

Permission granted to reproduce for educational use only.© Goodheart-Willcox Co., Inc. Valve Spring Construction Basically same for all engines (Honda)

Permission granted to reproduce for educational use only.© Goodheart-Willcox Co., Inc. Valve Spring Construction (Cont.) Spring tension –Stiffness of valve spring measured in psi or kPa Spring free length –Length of valve spring when removed from engine Spring closed length –Length of spring when installed with valve closed

Permission granted to reproduce for educational use only.© Goodheart-Willcox Co., Inc. Valve Spring Construction (Cont.) Valve float –Occurs when valve fails to close because spring is too weak Valve spring shim –Thin, machined washer used to increase spring tension Valve retainers and keepers –Lock valve spring onto valve

Permission granted to reproduce for educational use only.© Goodheart-Willcox Co., Inc. Valve Spring Construction (Cont.) Valve rotator –Turns valve to prevent carbon buildup and hot spots Valve stem cap –Helps prevent stem and rocker arm wear

Permission granted to reproduce for educational use only.© Goodheart-Willcox Co., Inc. Camshaft Construction Camshaft –Determines when valves open and close Many engines only use one Others use two or more Dual overhead cam engines –Have two camshafts per cylinder head One intake camshaft One exhaust camshaft

Permission granted to reproduce for educational use only.© Goodheart-Willcox Co., Inc. Camshaft Construction (Cont.) Cam lobes –Consists of nose, flank, heel, base diameter Camshaft lift –Distance valve opens Camshaft duration –How long valve stays open ( VW)

Permission granted to reproduce for educational use only.© Goodheart-Willcox Co., Inc. Camshaft Construction (Cont.) Valve timing –Valve opening and closing in relation to position of pistons Designed into camshaft Valve overlap –When both intake and exhaust valves in same cylinder are open

Permission granted to reproduce for educational use only.© Goodheart-Willcox Co., Inc. Camshaft Construction (Cont.) Camshaft thrust plate –Used to limit end play (front-to-rear movement) Cam bearings –Pressed into block or cylinder head Camshaft journals ride in cam bearings

Permission granted to reproduce for educational use only.© Goodheart-Willcox Co., Inc. Cam Housing and Cam Cover Cam housing –Casting that bolts to top of cylinder head Holds camshaft Cam cover –Lid over cam housing

Permission granted to reproduce for educational use only.© Goodheart-Willcox Co., Inc. Valve Lifters Valve lifters or tappets –Ride on camshaft lobes –Transfer motion to other parts of valve train Hydraulic valve lifters –Operate quietly by maintaining zero valve clearance (Chrysler)

Permission granted to reproduce for educational use only.© Goodheart-Willcox Co., Inc. Valve Lifters (Cont.) Mechanical lifters or solid lifters –Transfer cam lobe action to push rod Do not contain oil Roller lifter –Has small roller that rides on camshaft lobe OHC follower –Fits between camshaft and valve

Permission granted to reproduce for educational use only.© Goodheart-Willcox Co., Inc. Push Rod Construction Push rods –Metal tubes or rods used to transfer motion from lifters to rocker arms Push rod guide plates –Used to limit side movement of push rods

Permission granted to reproduce for educational use only.© Goodheart-Willcox Co., Inc. Rocker Arm Construction Rocker arms –Transfer valve train motion to valve stem tips ( Federal Mogul)

Permission granted to reproduce for educational use only.© Goodheart-Willcox Co., Inc. Variable Valve Timing System Alters valve timing as engine speed changes Optimizes engine power and efficiency at all operating speeds ( Honda)

Permission granted to reproduce for educational use only.© Goodheart-Willcox Co., Inc. Intake Manifold Construction Intake manifold –Holds throttle body –Has passages, called runners, going to each cylinder head port –Usually contain water jackets for cooling –Cast of iron, aluminum, or plastic ( Honda)

Permission granted to reproduce for educational use only.© Goodheart-Willcox Co., Inc. Intake Manifold Construction (Cont.) Manifold runners –Carry either air-fuel mixture or air to cylinder head ports Compression limiters –Metal inserts that limit deformation around bolt holes in plastic parts

Permission granted to reproduce for educational use only.© Goodheart-Willcox Co., Inc. Intake Manifold Construction (Cont.) Flame arrester –Located before engine intake manifold –Prevents backfire damage to air filter Variable induction system –Uses two sets of intake runners Controlled by butterfly valves –Aids engine efficiency and performance

Permission granted to reproduce for educational use only.© Goodheart-Willcox Co., Inc. Exhaust Manifold Construction Exhaust manifold –Routes burned exhaust gases from cylinder head exhaust port to exhaust pipe –Usually made of cast iron due to high temperatures