chap26 pps Automotive technology at University of Cambridge

start
Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition
By James D. Halderman

1

©©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.
2

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.

3

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

4

©©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)

5

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

6

©©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

7

©©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

8

©©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

9

©©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


New designs use cast combustion chambers rather than expensive 
machined chambers. These chambers are called by such names as 
polyspherical, hemiwedge, kidney­shaped, and pentroof. All 
cylinder head designs try to place the spark plug in an ideal location 
for best combustion, as shown here.

Figure 26–3
A General Motors Quad-4 engine
with a combustion chamber shape
called a modified pentroof. Note
the central location of the plug.

Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition
By James D. Halderman

11

©©2008
2009Pearson
PearsonEducation,
Education,Inc.
Inc.
Pearson
PearsonPrentice
PrenticeHall

Hall- -Upper
UpperSaddle
SaddleRiver,
River,NJ
NJ07458
07458


MULTIPLE VALVE COMBUSTION CHAMBERS
The power any engine produces is directly related to the amount of 
air–fuel mixture ignited in the cylinder. Increasing displacement is 
a common method of increasing engine  power.
Turbo charging and supercharging also increase engine power, but 
these increase engine cost as well. 
Adding more than two valves per cylinder permits more gas to flow 
into and out with greater velocity without excessive valve duration. 
The maximum amount of gas moving through the opening area of a 
valve depends on the distance around the valve and the degree to 
which it lifts open. 
12

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


More total area under is possible when two
smaller valves, rather than one larger valve,
are used at the same valve lift. Smaller
valves allow smooth low­speed operation. 

Figure 26–4 Comparing the valve
opening areas between two- and
three-valve combustion chambers
when the valves are open.

Figure 26–5 Audi five-valve cylinder head. This
design uses three intake valves (top) and two
exhaust valves (bottom).

Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition
By James D. Halderman

13

©©2008
2009Pearson
PearsonEducation,
Education,Inc.
Inc.
Pearson
PearsonPrentice
PrenticeHall
Hall- -Upper
UpperSaddle
SaddleRiver,
River,NJ
NJ07458
07458


INTAKE AND EXHAUST PORTS
The part of the intake or exhaust system passage cast in the head is 
called a port. Ports lead from manifolds to valves. Engines that 
have the intake port on one side of the head and the exhaust port on 
the opposite side are a cross­flow head design. 

The cross­flow head shown 
here allows the valve to be 
located and angled to permit 
efficient engine breathing.
It allows the spark plug to 
be near the center of the 
combustion chamber. 
All V­type engines have

cross­flow head design.

Figure 26–6 A typical two-valve cross- flow cylinder
head. The intake is on the top and the exhaust is on
the bottom.

Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition
By James D. Halderman

14

©©2008
2009Pearson
PearsonEducation,
Education,Inc.
Inc.
Pearson
PearsonPrentice
PrenticeHall
Hall- -Upper
UpperSaddle
SaddleRiver,
River,NJ
NJ07458
07458


At times, a restricting hump within a port may actually increase the 
airflow capacity of the port. It does this by redirecting flow to an 
area of the port that large enough to handle the flow. Modifications 

in the field, such as porting or relieving, would result in restricting 
the flow of such a carefully designed port. 

Figure 26–7
The top cylinder head
is stock and the
bottom
cylinder head has been
ported.

15

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 intake port in the head is relatively long, whereas the exhaust 
port is short. The long intake port wall is heated by coolant flowing 
through the head. The heat aids in vaporizing the fuel in the intake 
charge. The exhaust port is short so that the least amount of exhaust 
heat is transferred to the coolant. 

Figure 26–8 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.

Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition
By James D. Halderman

16

©©2008
2009Pearson
PearsonEducation,
Education,Inc.
Inc.
Pearson
PearsonPrentice
PrenticeHall
Hall- -Upper
UpperSaddle
SaddleRiver,
River,NJ

NJ07458
07458


CYLINDER HEAD RECONDITIONING SEQUENCE
Cylinder heads should be reconditioned using the following sequence:

1. Disassemble and thoroughly clean the heads.
(See Chapter 25.)
2. Check for cracks and repair as necessary.
(See Chapter 25.) 
3. Check the surface that contacts the engine block and 
machine if necessary.
4. Check valve guides and replace or service as necessary.
5. Grind valves and reinstall the valves in the cylinder head 
with new valve­stem seals.
6. Check valve spring force and installed height.
17

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


Disassembling the Cylinder Head  The engine should be cool 
(room temperature) before the cylinder heads are removed.
As mentioned in Chapter 6, the head bolts should be loosened in the 
reverse of the order used for tightening to avoid the possibility of 
warping.
In other words, the head bolts should be loosened from the outside 
and you should work your way toward the center of the head.
Remove the valves from the cylinder head as illustrated in Figure 
26–10.

18

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


Boing!
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.

Figure 26–10
A valve spring compressor is used
to compress the valve spring before
removing the keepers (locks).

Continued
Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition
By James D. Halderman

19

©©2008
2009Pearson

PearsonEducation,
Education,Inc.
Inc.
Pearson
PearsonPrentice
PrenticeHall
Hall- -Upper
UpperSaddle
SaddleRiver,
River,NJ
NJ07458
07458


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.

Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition
By James D. Halderman

20

©©2008
2009Pearson
PearsonEducation,
Education,Inc.
Inc.
Pearson
PearsonPrentice
PrenticeHall
Hall- -Upper
UpperSaddle
SaddleRiver,
River,NJ
NJ07458
07458


The surface of the head must be thoroughly cleaned and inspected as 
follows:

The surface is first scraped and then draw­filed to remove any 
small burrs.
The head should be checked in five planes as shown in Figures 
26–12 and 26–13 for warpage, distortion, bend, and twist.

Figure 26–12
A precision ground straight- edge and
a feeler gauge are used to check the

cylinder head for flatness.

Continued
Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition
By James D. Halderman

21

©©2008
2009Pearson
PearsonEducation,
Education,Inc.
Inc.
Pearson
PearsonPrentice
PrenticeHall
Hall- -Upper
UpperSaddle
SaddleRiver,
River,NJ
NJ07458
07458


The head should not vary by over 0.002 inches (0.05 millimeters) in 
any 6­inch (15­centimeter) length, or by more than 0.004 inches. 
Always check the manufacturer’s recommended specs.

Figure 26–13
Cylinder heads should be checked in five planes for warpage, distortion, bend, or twist.

Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition
By James D. Halderman

22

©©2008
2009Pearson
PearsonEducation,
Education,Inc.
Inc.
Pearson
PearsonPrentice
PrenticeHall
Hall- -Upper
UpperSaddle
SaddleRiver,
River,NJ
NJ07458
07458


NOTE: The cylinder head surface that mates with the top deck of the
block is often called the fire deck.

The head should not vary by over 0.002 inches (0.05 millimeters) in 
any 6­inch (15­centimeter) length, or by more than 0.004 inches 
overall. Always check the manufacturer’s recommended specs

Cylinder Head Resurfacing The head should be resurfaced if there 
is any roughness caused by corrosion of the head gasket. This can 

be felt on the head surface when you rub your fingernail across it.
In precision engine rebuilding, both the head and the block deck are 
resurfaced as a standard practice.
The head will usually have some warpage when the engine is 
disassembled.
23
Automotive
Technology:
Principles,
Diagnosis,
and
Service,
3rd
Edition
©
©
2008
2009
Pearson
Pearson
Education,
Education,
Inc.
Inc.
  By James D. Halderman
Pearson
PearsonPrentice
PrenticeHall
Hall- -Upper
UpperSaddle

SaddleRiver,
River,NJ
NJ07458
07458


Figure 26–14 A cylinder head being resurfaced.

NOTE: Always check the cylinder head thickness and specifications to 
be sure material can be safely removed from the surface. Some 
manufacturers do not recommend machining, but require cylinder head 
replacement if cylinder head surface flatness is not within specifications. 
Aluminum cylinder heads are usually straightened before resurfacing.
Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition
By James D. Halderman

24

©©2008
2009Pearson
PearsonEducation,
Education,Inc.
Inc.
Pearson
PearsonPrentice
PrenticeHall
Hall- -Upper
UpperSaddle
SaddleRiver,
River,NJ

NJ07458
07458


Surface Finish  As important as size of the part. Surface finish is 
measured in units called microinches (abbreviated µ in.). The 
symbol in front of the inch abbreviation is the Greek letter mu. One 
microinch equals 0.000001 inches (0.025 micrometers [µm]). The 
usual method of expressing surface finish is by the arithmetic 
average roughness height, abbreviated RA, which is the average of 
the distances of all peaks and valleys from the mean (average) line.
Figure 26–15 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.

Continued
Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition
By James D. Halderman

25

©©2008
2009Pearson
PearsonEducation,
Education,Inc.
Inc.
Pearson
PearsonPrentice
PrenticeHall
Hall- -Upper
UpperSaddle

SaddleRiver,
River,NJ
NJ07458
07458