Halderman ch030 lecture

© 2011 Pearson Education, Inc.All Rights Reserved

Automotive Technology, Fourth EditionJames Halderman

CYLINDER HEAD AND VALVE GUIDE SERVICE

30

30 CYLINDER HEAD AND VALVE GUIDE SERVICE



ObjectivesObjectives

• The student 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.




ObjectivesObjectives

• The student should be able to:– List the steps necessary to recondition a

cylinder head. – Describe how to inspect and measure valve

guides. – Discuss valve guide repair options.




INTRODUCTIONINTRODUCTION




IntroductionIntroduction

• Repair of cylinder heads is the most frequent engine repair

• Highest temperatures and pressures in the engine are in the combustion chamber of the cylinder head

• Valves open and close thousands of times during engine operation




CYLINDER HEADSCYLINDER HEADS




Cylinder HeadsCylinder Heads

• Construction– Supports the valves and valve train– Handles flow of intake, exhaust gases,

coolant, and sometimes oil




Figure 30-1 The seats and guides for the valves are in the cylinder head as well as the camshaft and the entire valve train if it is an overhead camshaft design.





• Design Features– Squish area– Quench area– Spark plug placement





• Design Features– Surface-to-volume ratio– Valve shrouding– Crossflow valve placement




Figure 30-2 A wedge-shaped combustion chamber showing the squish area where the air-fuel mixture is squeezed, causing turbulence that pushes the mixture toward the spark plug.




Figure 30-3 Locating the spark plug in the center of the combustion chamber reduces the distance the flame front must travel.




Figure 30-4 The combustion chamber of the 5.7 liter Chrysler Hemi cylinder head shows the two spark plugs used to ensure rapid burn for best power and economy with the lowest possible exhaust emissions.




Figure 30-5 The shrouded area around the intake valve causes the intake mixture to swirl as it enters the combustion chamber.




Figure 30-6 A typical cross flow cylinder head design, where the flow into and out of the combustion chamber is from opposite sides of the cylinder head.




Cylinder Heads Cylinder Heads

• Combustion Chamber Designs– Created as two parts– Upper part: cylinder head and walls– Lower part: top of the piston





• Combustion Chamber Designs– Most common shapes include:

• Wedge• Pentroof• Hemi

?





• Four-Valve Cylinder Heads– More than two valves allow more gas to

flow through the engine– Valve duration: number of degrees by

which the crankshaft rotates when the valve is off the valve seat





• Four-Valve Cylinder Heads– Maximum amount of gas moving through

the opening of a valve depends on the distance around the valve and the degree to which it lifts open





• Four-Valve Cylinder Heads– The distance around a valve is calculated

by the equation:• pi × D or 3.1416 × valve diameter





• Four-Valve Cylinder Heads– Four valves on the pentroof design are

operated with dual overhead camshafts or with single overhead camshafts and rocker arms





• Four-Valve Cylinder Heads– Four valves make it is possible to place the

sparkplug at the center of the combustion chamber




Figure 30-7 Method for measuring the valve opening space.




Figure 30-8 Comparing the valve opening areas between a twoand three-valve combustion chamber when the valves are open.




Figure 30-9 Typical four-valve head. The total area of opening of two small intake valves and two smaller exhaust valves is greater than the area of a two-valve head using much larger valves. The smaller valves also permit the use of smaller intake runners for better low-speed engine response.




Figure 30-10 Four valves in a pentroof combustion chamber.




Figure 30-11 An Audi five-valve cylinder head, which uses three intake valves and two exhaust valves.




INTAKE INTAKE AND EXHAUST PORTSAND EXHAUST PORTS




Intake and Exhaust PortsIntake and Exhaust Ports

• Purpose and Function– Port: part of the intake or exhaust system

passage cast in the cylinder head





• Purpose and Function– Ports lead from the manifolds to the valves





• Purpose and Function– Inline engines may have both on the same

side of the engine– Cylinders on older engines could share a

port due to restricted space called Siamese ports




Intake and Exhaust Ports Intake and Exhaust Ports

• Intake Ports– Larger ports and better breathing are

possible in engines when the intake and exhaust ports are on opposite sides





• Intake Ports– A restricting hump within a port could

increase its airflow capacity





• Intake Ports– Modifications in the field, such as porting or

relieving, restrict the flow of a carefully designed port





• Intake Ports– Intake manifold and combustion chamber

design work together to cause the air-fuel mixture to swirl in the combustion chamber




Figure 30-12 The intake manifold design and combustion chamber design both work together to cause the air-fuel mixture to swirl as it enters the combustion chamber.





• Exhaust Ports– Designed to allow free flow of exhaust

gases from the engine– Shorter than the intake ports to help

reduce the amount of heat transferred to the coolant




Figure 30-13 A port-injected engine showing the straight free-flowing intake and exhaust ports.




CYLINDER HEAD CYLINDER HEAD PASSAGESPASSAGES




Cylinder Head PassagesCylinder Head Passages

• Coolant Flow Passages– From the coolest to the warmest portions of

the engine – Water pump takes the coolant from the

radiator





• Coolant Flow Passages– Circulated through the block and directed

around the cylinders– Flows upward through the gasket to the

cooling passages in the cylinder head





• Coolant Flow Passages– Heated coolant is collected and returned to

the radiator to be cooled and recycled





• NOTE: Reversed-flow cooling systems, such as that used on the Chevrolet LT1 V-8, send the coolant from the radiator to the cylinder heads first. This results in a cooler cylinder head and allows for more spark advance without engine-damaging detonation.




Figure 30-14 A cutaway head showing the coolant passages in green.





• Head Gasket Holes– Gasket surface of head leading to cooling

passages has large holes





• Head Gasket Holes– Head gasket performs an important coolant

flow function when openings are too large





• Head Gasket Holes– Special-size and smaller holes correct the

coolant flow rate at each opening





• Head Gasket Holes– Correct head gasket installation is

necessary for proper engine cooling




Figure 30-15 Coolant flows through the cylinder head, and the passages are sealed by the head gasket.





• Lubricating Oil Passages– Lubricating oil is delivered to overhead

valve mechanism– Special openings in head gasket allow oil to

pass between the block and head without leaking





• Lubricating Oil Passages– Oil returns to the oil pan through oil return

passages





• NOTE: Many aluminum cylinder heads have smaller-than-normal drainback holes. If an engine has excessive oil consumption, check the drain holes before removing the engine.




CYLINDER HEAD CYLINDER HEAD SERVICINGSERVICING




Cylinder Head ServicingCylinder Head Servicing

• Cylinder Head Servicing Sequence– Disassemble and thoroughly clean the

heads– Check for cracks and repair as necessary





• Cylinder Head Servicing Sequence– Check the surface that contacts the engine

block and machine, if necessary





• Cylinder Head Servicing Sequence– Check valve guides and replace or service,

as necessary– Grind valves and reinstall them in the

cylinder head with new valve stem seals





• Disassembling Overhead Camshaft Head– When one-piece bearings are used, the

valve springs have to be compressed with a fixture or the finger follower has to be removed





• Disassembling Overhead Camshaft Head– When bearing caps are used, loosen valve

springs alternately so that bending loads are not placed on either the cam or bearing caps




Figure 30-16 Overhead camshafts may be (a) held in place with bearing caps, (b) supported by towers, or (c) fitted into bearing bores machined directly into the head.




Figure 30-17 Always follow the specified loosening sequence to prevent valve spring tension from bending the camshaft.





• Valve Train Disassembly– Disassemble cylinder head– Keep the top part of the pushrod at the top





• Valve Train Disassembly– Keep the rocker arms with the same

pushrods– Intake and exhaust valve springs must be

kept with the correct valve




Figure 30-18 Pushrods can be kept labeled if stuck through a cardboard box. Individual parts become worn together. Using cardboard is a crude but effective material to keep all valve train parts together and labeled exactly as they came from the engine.





• Cylinder Head Inspection– Clean surface and inspect as follows:

• Remove old gasket material and draw a file across the surface of the head to remove any small burrs





• Cylinder Head Inspection– Clean surface and inspect as follows:

• Check the head in five planes for warpage, distortion, bends, and twists (slide a 0.004 in. (0.1 mm) feeler gauge under a precision straightedge held against the head surface; clearance between the two should not vary by more than 0.004 in. overall)





• Cylinder Head Inspection– NOTE: The cylinder head surface that

mates with the top deck of the block is often called the fire deck.





• Cylinder Head Inspection– NOTE: Always check the cylinder head

thickness and specifications to be sure that material can be safely removed from the surface. Some manufacturers do not recommend any machining, but rather require cylinder head replacement if cylinder head surface flatness is not within specifications.




Figure 30-19 Cylinder heads should be checked in five planes for warpage, distortion, bend, and twist.




Figure 30-20 A precision ground straightedge and a feeler gauge are used to check the cylinder head for flatness.




ALUMINUM CYLINDERALUMINUM CYLINDERHEAD STRAIGHTENINGHEAD STRAIGHTENING




Aluminum Cylinder Head Aluminum Cylinder Head Straightening Straightening

• Purpose and Function– STEP 1: Determine the amount of warpage

with a straightedge and thickness (feeler) gauge. Cut shim stock (thin strips of metal) to one-half of the amount of the warpage. Place shims of this thickness under each end of the head.





• Purpose and Function– STEP 2: Tighten the center of the cylinder

head down on a strong, flat base. A 2 in. thick piece of steel that is 8 in. wide by 20 in. long makes a good support for the gasket surface of the cylinder head (use antiseize compound on the bolt threads to help in bolt removal).





• Purpose and Function– STEP 3: Place the head and base in an oven

for five hours at 500°F (260°C). Turn the oven off and leave the assembly in the oven.





• Purpose and Function– NOTE: If the temperature is too high, the

valve seat inserts may fall out of the head! At 500°F, a typical valve seat will still be held into the aluminum head with a 0.002 in. interference fit based on calculations of thermal expansion of the aluminum head and steel insert.




Figure 30-21 Warped overhead camshaft cylinder head. If the gasket surface is machined to be flat, the camshaft bearings will still not be in proper alignment. The solution is to straighten the cylinder head or to align bore the cam tunnel.




Aluminum Cylinder Head Aluminum Cylinder Head StraighteningStraightening

• Purpose and Function– Cool head in oven at least four to five hours– Heating/cooling process can be repeated if

necessary




Aluminum Cylinder Head Aluminum Cylinder Head StraighteningStraightening

• Purpose and Function– Gasket surface (fire deck) can be machined

in the usual manner after straightening




CYLINDER HEADCYLINDER HEADRESURFACINGRESURFACING




Cylinder Head ResurfacingCylinder Head Resurfacing

• Refinishing Methods– Two common methods:

• Milling or broaching uses metal-cutting tool bits fastened in a disc





• Refinishing Methods– Two common methods:

• Grinding uses a large-diameter abrasive wheel

– Both can be done with table-type or precision-type resurfacers





• Refinishing Methods– NOTE: Resurfacing the cylinder head

changes the compression ratio of the engine by about 1/10 point per 0.01 in. of removed material. For example, the compression ratio would be increased from 9.0:1 to 9.2:1 if 0.02 in. were removed from a typical cylinder head.




Figure 30-22 A cast-iron cylinder head being resurfaced using a surface grinder.





• Surface Finish– Measured in microinches (abbreviated “μ

in.”)– Arithmetic average roughness height (RA)

is used to express surface finish





• Surface Finish– Root-mean-square (RMS) classification is

becoming obsolete





• Surface Finish– Surface finish roughness recommendations

for cylinder heads and blocks include the following:

• Cast iron– Maximum: 110 RA (125 RMS)







• Cast iron– Minimum: 30 RA (33 RMS)







• Cast iron– Recommended range: 60 to 100 RA (65 to

110 RMS)







• Aluminum– Maximum: 60 RA (65 RMS)







– Minimum: 30 RA (33 RMS)







– Recommended range: 50 to 60 RA (55 to 65 RMS)




Figure 30-23 A graph showing a typical rough surface as would be viewed through a magnifying glass. RA is an abbreviation indicating the average height of all peaks and valleys.




INTAKE MANIFOLD INTAKE MANIFOLD ALIGNMENTALIGNMENT




Intake Manifold AlignmentIntake Manifold Alignment

• Purpose– Grinding gasket surfaces of the heads may

cause intake manifold to not fit correctly– Remove enough metal to rematch the ports

and bolt holes




Figure 30-24 The material that must be removed for a good manifold fit.





• Procedure– Machine shops have tables that specify the

exact amount of metal to be removed– Remove some metal from the front and

back gasket surfaces of closed-type intake manifolds





• CAUTION: Do not remove any more material than is necessary to restore a flat cylinder head-to-block surface. Some manufacturers limit total material that can be removed from the block deck and cylinder head to 0.008 in. (0.2 mm).





• CAUTION: Removal of material from the cylinder head of an overhead camshaft engine shortens the distance between the camshaft and the crankshaft. This causes the valve timing to be retarded unless a special copper spacer shim is placed between the block deck and the gasket to restore proper crankshaft-to-camshaft centerline dimension.




Figure 30-25 Using an intake manifold template to check for the proper angles after the cylinder heads have been machined.




VALVE GUIDESVALVE GUIDES




Valve GuidesValve Guides

• Types– Integral with the head casting in cast-iron

heads– Removable or pressed-in valve guides and

valve seat inserts are always used in aluminum heads




Figure 30-26 An integral valve guide is simply a guide that has been drilled into the cast-iron cylinder head.




Figure 30-27 All aluminum cylinder heads use valve guide inserts.




Figure 30-28 Valve guides often wear to a bell-mouth shape to both ends due to the forces exerted on the valve by the valve train components.





• Valve Stem-to-Guide Clearance– Intake valve: 0.001 to 0.003 in. (0.025 to

0.076 mm)– Exhaust valve: 0.002 to 0.004 in. (0.05 to

0.1 mm)





• HINT: A human hair is about 0.002 in. (0.05 mm) in diameter. Therefore, the typical clearance between a valve stem and the valve guide is only the thickness of a human hair.




Valve Guides Valve Guides

• Measuring Valve Guides– Measure valves for stem wear before

measuring valve guides– Valve guides are measured in the middle

with a small-hole gauge





• Measuring Valve Guides– Gauge size is checked with a micrometer– Guide is then checked at each end





• Measuring Valve Guides– Place expanded part of the ball crosswise

to the engine where the greatest amount of wear exists





• Measuring Valve Guides– Valve stem diameter is subtracted from the

valve guide diameter– Valve stem-to-guide clearance can also be

checked using a dial indicator (gauge)

?




Figure 30-29 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.




Figure 30-30 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-stem clearance.




Figure 30-31 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 specifications because it does not give the guide-to-stem clearance directly. The valve is usually held open to its maximum operating lift.




Figure 30-32 Sectional view of a knurled valve guide.





• Oversize Stem Valves– Some domestic manufacturers recommend

replacing worn valve guides with oversize (OS) stems

– Sizes include 0.003, 0.005, 0.015, and 0.03 in.





• Oversize Stem Valves– Valve guide is reamed or honed to fit the

oversize stem – Clearance of the valve stem in the guide is

the same as the original





• Oversize Stem Valves– Oil clearance and heat transfer properties

do not change

• NOTE: Many remanufacturers of cylinder heads use oversize valve stems to simplify production.




VALVE GUIDE VALVE GUIDE REPLACEMENTREPLACEMENT




Valve Guide Replacement Valve Guide Replacement

• Purpose– Replacement always recommended when

valve assembly is reconditioned





• Purpose– Replacement valve guides can be installed

to repair worn integral guides





• Valve Guide Sizes– Three common sizes:

• 5/16 or 0.313 in.• 11/32 or 0.343 in.• 3/8 or 0.375 in.




Figure 30-33 Valve guide replacement procedure.




Valve Guide ReplacementValve Guide Replacement

• Valve Guide Inserts– Integral valve guides can be reconditioned

with valve guide inserts– Two types commonly used:

• Thin-walled bronze alloy sleeve bushing





• Valve Guide Inserts– Two types commonly used

• Spiral bronze alloy bushing





• Valve Guide Inserts– Installation kit includes all necessary

reamers, installing sleeves, broaches, burnishing tools, and cutoff tools

– Valve guide must be bored to a large enough size to accept the thin-walled insert sleeve




Figure 30-34 A type of fixture required to bore the valve guide to accept a thin-walled insert sleeve.




Figure 30-35 Trimming the top of the thin-walled insert.





• Spiral Bronze Insert Bushings– Screwed into a thread that is put in the

valve guide– Tightened on an inserting tool and screwed

into the spring end of the guide until the bottom is flush with the seat end





• Spiral Bronze Insert Bushings– Bushing is trimmed to one coil above the

spring end of the guide– Bushing is temporarily secured with a

plastic serrated retainer and a worm gear clamp





• Spiral Bronze Insert Bushings– Broach is driven through the bushing to

firmly seat it in the threads– Bushing is reamed or honed to size before

the retainer is removed





• Spiral Bronze Insert Bushings– Final step is to trim the end with a special

cutoff tool

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