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crankshaft bearings and related components > Cylinder head fundamentals > Flashcards

Cylinder head fundamentals Flashcards

1
Q

cylinder head of a diesel engine

A

subjected to extremely high running pressure and high operating temperature
constructed of high quality materials and special alloys

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2
Q

main functions of a cylinder head

A

form a rigid top to seal the combustion chamber
contain valves and ports which rout the flow of inlet and exhaust gas
retain valve operating mechanisms and fuel injectors
contain passages for the flow of coolant and lubricating oils
provide a means of attaching external components

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3
Q

cylinder head construction

A

cast iron alloy

aluminum

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4
Q

cylinder heads used in diesel engines are made from

A

cast iron alloy to withstand higher heat and pressure

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5
Q

cylinder heads used on gasoline engines

A

aluminum for lighter weight and better heat transfer

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6
Q

factors that will influence cylinder head design are

A

engine application
horsepower rating
maximum rpm
type of induction

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7
Q

cylinder heads can be

A

two or four heads per cylinder

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8
Q

advantage of four valve cylinder heads

A

increase in volumetric efficiency
better turbulence for mixing fuel and air
lighter and generate less inertia

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9
Q

ports

A

direct air flow in and out of the cylinder

shape is carefully designed to achieve the correct amount of airflow

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10
Q

inlet ports

A

direct air from the manifold to the valve and into the cylinder

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11
Q

exhaust ports

A

direct exhaust gas from the valve to the manifold

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12
Q

injector tube

A

is a cylindrical sleeve usually made from copper brass or stainless steel
pressed fit into bore in the cylinder head
positions the fuel injector in relation to the combustion chamber
surrounded by coolant to cool during operation

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13
Q

why must there be a seal between the injector tube and cylinder head

A

to prevent coolant form leaking past the tube and into the combustion chamber and crank case
and to prevent combustion gases from leaking past the tube into the cooling system

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14
Q

coolant and lubrication passageways

A

surround cylinder head components and carry heat away during operation

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15
Q

coolant directional nozzles

A

copper or brass inserts pressed into the inlet of the cooling passages of a cylinder head to direct coolant to critical areas

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16
Q

valve assembly function

A

open and close during intake and exhaust

seal during compression and power events

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17
Q

valve terminology

A 
valve lock groove
stem 
fillet 
valve face 
margin
valve head 
tip
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18
Q

why are exhaust valves usually made from better quality material than intake

A

operates with higher temperature and comes into contact with corrosive gases

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19
Q

why are some valves machined slightly smaller in diameter on the lower end

A

to act as a carbon scraper to keep valve clean and reduce carbon build up

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20
Q

valve cooling

A

cooled by incoming air charge and heat transfer to the cylinder head
75% of cooling of solid type valves occurs between valve face and valve seat
25% from valve stem to valve guide

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21
Q

sodium cooled valve are used when

A

addition cooling is needed in severe duty applications

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22
Q

how do sodium cooled valves work

A

valve is hollow and filled with sodium crystals that will liquefy when heated
liquid sodium then shakes with valve movement increasing heat transfer through rod stem

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23
Q

valve seats

A

create combustion chamber seal and allow for proper valve cooling
precision machined to a precise angle

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24
Q

valve springs

A

keep valve face in contact with the seat

keep cam follower in contact with cam lobe as engine rpm increases

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25
Q

types of valve springs

A

single coil
double coil
progressive or variable

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26
Q

single type spring

A

often have a flat inner damper coil to counter act vibrations at higher rpm

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27
Q

dual type spring

A

have an inner and outer spring to increase spring tension

can operate at higher rmp with less chance of valve float

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28
Q

progressive or variable spring

A

have coils wound closer together at one end for a variable rate of spring tension as it is compressed

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29
Q

what is valve float

A

what a spring allows the valve to oscillate uncontrolled resulting in valves not sealing properly resulting in loss of power and damaged valve mechanisms

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30
Q

spring seat

A

helps keep spring centered over guide

provides hardened surface to prevent erosion of casting material

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31
Q

valve retainers and locks

A

keeps the valve centered
keeps the spring and valve as a unit
sometimes referred to as collets or keepers

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32
Q

positive valve rotators

A

provides a changing wear surface and creates a wiping action at cleans the valve of carbon
commonly used in place of spring retainers

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33
Q

valve seals

A

control the lubrication of the valve stem
without them an excessive amount of oil would be consumed
generally made of synthetic rubber

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34
Q

two types of valve seals

A

positive

non-positive

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35
Q

positive type valve seals

A

have a Teflon insert for wear resistance and reduced friction
provides the best control of valve stem lubrication

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36
Q

non positive valve seal

A

act as a shield or deflector
up and down with the valve stem
commonly referred to as umbrella type

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37
Q

rocker arms

A

form the link between the push rod and the valve tip

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38
Q

rocker arm ratio

A

determined by comparing the dimensions of the center line of the pivot point and the centerline of the contact points on either side of the rocker arm

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39
Q

valve bridges (crossheads)

A

used on cylinder heads with 4 valves per cylinder
allows one rocker arm to open both valves simultaneously
positioned by a pin that is pressed into cylinder head casting
engine may have adjustable or non adjustable bridges

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40
Q

valve cover

A

keeps out dirt and moisture

contains oil that lubricates valve operating mechanism

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41
Q

cylinder head gaskets are

A

most complex in design
must resist high temp and pressure
subject to expansion and contraction and corrosive elements

42
Q

two types of head gaskets

A

steel and composition

43
Q

steel gaskets

A

offer maximum resistance to forces of pressure and heat

lack conformability

44
Q

composition gaskets

A

multi layer construction

offer maximum conformability

45
Q

advantages of using cap screws for cylinder heads

A

easy removal and installation

clear access to cylinder block deck and liner after head removal

46
Q

disadvantages of cap screws on cylinder heads

A

threads are subject to stress during torque procedures

threads can become damaged during removal and install

47
Q

advantages of cylinder head studs

A

aid in alignment
more consistent torque value provide grater clamp force
stress on block threads is reduced

48
Q

disadvantages of cylinder head studs

A

more room required for disassembly
reduced access around cylinders
studs must be removed for deck machining

49
Q

why should you remove fuel injectors before lifting off the cylinder head

A

because injector heads can protrude below the machined surface of the cylinder head and can be easily damaged

50
Q

a damaged fuel injector tip can cause

A

altered spray pattern witch can lead to exhaust smoke loss of power and piston or liner damage

51
Q

when removing cylinder head studs they should be

A

loosened in a sequence to release clamping load evenly to prevent damage

52
Q

when visually checking the cylinder head for cracks you should pay close attention to these areas

A

valve seats

injector holes

53
Q

when preforming a bench test for valve leakage

A

rest the head on a bench with the valve surface vertical and fill the ports with liquid and watch for sings of leakage

54
Q

combustion or compression leakage of a head gasket

A

indicated by blow or burnt out sections

55
Q

coolant or oil leakage of a head gasket

A

indicated by damaged grommets or eroded sections

56
Q

compressing the valve springs for removal is done with

A

a valve spring compressing tool

57
Q

when removing valve springs with the compressing tool you may have to

A

tap the valve locks with a soft face hammer to release them from the tapered locks

58
Q

if the valve will not pass through the guide easily

A

may be a burr on the valve stem tip remove the burr with a flat smooth file to prevent valve damage

59
Q

before pressure testing a cylinder head

A

make sure all coolant passages are sealed

60
Q

when pressure testing the cylinder head

A

run a maximum pressure of 20 to 40 psi on the coolant passages
heat the cylinder head in hot water at 180 to 200 degrees for 15 to 20 min

61
Q

when measuring the cylinder head for flatness

A

use a straight edge and try to insert a .0015” feeler gauge

62
Q

high concentration of minerals in water when mixed with coolant will show up as

A

white scale

63
Q

over concentration of coolant cooling system chemicals will cause

A

green blue deposits

64
Q

insufficient corrosion inhibitors in the cooling system will cause

A

rust

65
Q

worn valve guides will cause

A

accelerated wear of valve face and seat preventing from sealing resulting in loss of power and excessive oil consumption

66
Q

two most common valve seat angles

A

30 and 45 degrees

67
Q

30 degree angle of a valve face

A

often used on intake valves because it has better air flow characteristics

68
Q

45 degree angle of a valve face

A

often used on exhaust valves because it creates more sealing force and heat transfer and helps keep the seat clean

69
Q

before regrinding a valve face you should check for

A

valve run out

valves with excessive run out should be replaced

70
Q

after regrinding a valve face the margin of the valve should not measure less than

A

1/2 the margin of a new valve

a valve with insufficient margin will run to hot and burn out premature

71
Q

two methods for repairing integral valve guides

A

Knurling

repair sleeve

72
Q

valve guide repair sleeve

A

most common type of valve guide repair

73
Q

knurling a integral valve sleeve

A

special die is rolled down the valve guide to expand the metal then honed to specific dimension

74
Q

tools for removing valve guides

A

ball peen hammer or air chisel

75
Q

when installing valve sleeve back into cylinder head you should

A

drive the valve sleeve in the opposite direction from witch you drove it out
use a limiting sleeve to install to proper depth

76
Q

removal of valve seat inserts

A

use a special chisel
weld a bead around the insert to shrink
use an insert puller

77
Q

insert puller

A

safest and easiest way to remove a valve seat insert

78
Q

after installation of a valve seat insert you should check for

A

concentricity using a special concentricity gauge

runout should not exceed .002”

79
Q

tools used for valve seat refinishing

A

valve seat grinding stones or cutters

80
Q

when using valve seat grinder

A

mounted on holder and driven at high speeds by electric or air powered driver

81
Q

valve seat cutters

A

usually turned by hand

82
Q

valve seats can be reground for an interference fit by

A

grinding the valve seat angle 1 to 1/2 degrees greater then the valve face
or grinding the valve face 1 to 1/2 smaller then the valve seat

83
Q

interference fit of a valve face

A

will raise the initial seat pressure and promote quick seating
will wear to full width in a short time after start up

84
Q

when checking the valve face for proper seating

A

spread a light film of Prussian blue on the valve face and snap the valve face against the seat

85
Q

regrinding a valve seat normally done in three stages to produce the proper profile

A

first use a 45 to remove worn or damaged areas
then use a 15 to move the sealing face to proper location on valve
finish with a 60 to narrow the seat to proper width

86
Q

if a valve seat is to wide

A

it will lower seating force and cause carbon build up leakage and poor cooling

87
Q

if a valve seat is to narrow

A

reduced contact area poor cooling and rapid wear

88
Q

free length of a valve spring

A

is the free standing or uncompressed length of a spring

89
Q

maximum allowable out of square on a valve spring

A

1/16”

springs with out of square will place side load on valves as they open and close

90
Q

when testing spring tension

A

test under a specific load at a given height

91
Q

low valve spring tension will cause

A

poor valve sealing
poor valve cooling
valve float or flutter

92
Q

worn or damaged threads on a rocker arm

A

will make valve adjustments impossible or difficult

93
Q

a cracked tubular pushrod that fills with oil will cause

A

greater mass and creates more valve train inertia

94
Q

pushrods will bend under normal loads and return to normal a permanently bent rod can be the result of

A

fatigue
mechanical failure
service problem

95
Q

basic check for push rod runout

A

roll along a flat surface

96
Q

after installing valve springs

A

check for proper spring height
if springs are to loose shims can be installed
no more then 2 shims with a total thickness of .060”

97
Q

when pressure testing valves before installation

A

apply a vacuum of 20 HG on the valve head
if there is a drop of 10 HG or more that is to excessive
disassemble and find the cause

98
Q

make sure to adjust vale bridges before valve clearance because

A

movement of the crosshead or bridge adjusting screw will the change valve clearance

99
Q

excessive valve clearance can cause

A

poor engine performance and noisy valve train

100
Q

insufficient valve clearance can cause

A

poor engine performance or damage to valve train components

crankshaft bearings and related components (3 decks)

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