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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
types of valve springs
single coil double coil progressive or variable
26
single type spring
often have a flat inner damper coil to counter act vibrations at higher rpm
27
dual type spring
have an inner and outer spring to increase spring tension | can operate at higher rmp with less chance of valve float
28
progressive or variable spring
have coils wound closer together at one end for a variable rate of spring tension as it is compressed
29
what is valve float
what a spring allows the valve to oscillate uncontrolled resulting in valves not sealing properly resulting in loss of power and damaged valve mechanisms
30
spring seat
helps keep spring centered over guide | provides hardened surface to prevent erosion of casting material
31
valve retainers and locks
keeps the valve centered keeps the spring and valve as a unit sometimes referred to as collets or keepers
32
positive valve rotators
provides a changing wear surface and creates a wiping action at cleans the valve of carbon commonly used in place of spring retainers
33
valve seals
control the lubrication of the valve stem without them an excessive amount of oil would be consumed generally made of synthetic rubber
34
two types of valve seals
positive | non-positive
35
positive type valve seals
have a Teflon insert for wear resistance and reduced friction provides the best control of valve stem lubrication
36
non positive valve seal
act as a shield or deflector up and down with the valve stem commonly referred to as umbrella type
37
rocker arms
form the link between the push rod and the valve tip
38
rocker arm ratio
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
39
valve bridges (crossheads)
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
40
valve cover
keeps out dirt and moisture | contains oil that lubricates valve operating mechanism
41
cylinder head gaskets are
most complex in design must resist high temp and pressure subject to expansion and contraction and corrosive elements
42
two types of head gaskets
steel and composition
43
steel gaskets
offer maximum resistance to forces of pressure and heat | lack conformability
44
composition gaskets
multi layer construction | offer maximum conformability
45
advantages of using cap screws for cylinder heads
easy removal and installation | clear access to cylinder block deck and liner after head removal
46
disadvantages of cap screws on cylinder heads
threads are subject to stress during torque procedures | threads can become damaged during removal and install
47
advantages of cylinder head studs
aid in alignment more consistent torque value provide grater clamp force stress on block threads is reduced
48
disadvantages of cylinder head studs
more room required for disassembly reduced access around cylinders studs must be removed for deck machining
49
why should you remove fuel injectors before lifting off the cylinder head
because injector heads can protrude below the machined surface of the cylinder head and can be easily damaged
50
a damaged fuel injector tip can cause
altered spray pattern witch can lead to exhaust smoke loss of power and piston or liner damage
51
when removing cylinder head studs they should be
loosened in a sequence to release clamping load evenly to prevent damage
52
when visually checking the cylinder head for cracks you should pay close attention to these areas
valve seats | injector holes
53
when preforming a bench test for valve leakage
rest the head on a bench with the valve surface vertical and fill the ports with liquid and watch for sings of leakage
54
combustion or compression leakage of a head gasket
indicated by blow or burnt out sections
55
coolant or oil leakage of a head gasket
indicated by damaged grommets or eroded sections
56
compressing the valve springs for removal is done with
a valve spring compressing tool
57
when removing valve springs with the compressing tool you may have to
tap the valve locks with a soft face hammer to release them from the tapered locks
58
if the valve will not pass through the guide easily
may be a burr on the valve stem tip remove the burr with a flat smooth file to prevent valve damage
59
before pressure testing a cylinder head
make sure all coolant passages are sealed
60
when pressure testing the cylinder head
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
when measuring the cylinder head for flatness
use a straight edge and try to insert a .0015" feeler gauge
62
high concentration of minerals in water when mixed with coolant will show up as
white scale
63
over concentration of coolant cooling system chemicals will cause
green blue deposits
64
insufficient corrosion inhibitors in the cooling system will cause
rust
65
worn valve guides will cause
accelerated wear of valve face and seat preventing from sealing resulting in loss of power and excessive oil consumption
66
two most common valve seat angles
30 and 45 degrees
67
30 degree angle of a valve face
often used on intake valves because it has better air flow characteristics
68
45 degree angle of a valve face
often used on exhaust valves because it creates more sealing force and heat transfer and helps keep the seat clean
69
before regrinding a valve face you should check for
valve run out | valves with excessive run out should be replaced
70
after regrinding a valve face the margin of the valve should not measure less than
1/2 the margin of a new valve | a valve with insufficient margin will run to hot and burn out premature
71
two methods for repairing integral valve guides
Knurling | repair sleeve
72
valve guide repair sleeve
most common type of valve guide repair
73
knurling a integral valve sleeve
special die is rolled down the valve guide to expand the metal then honed to specific dimension
74
tools for removing valve guides
ball peen hammer or air chisel
75
when installing valve sleeve back into cylinder head you should
drive the valve sleeve in the opposite direction from witch you drove it out use a limiting sleeve to install to proper depth
76
removal of valve seat inserts
use a special chisel weld a bead around the insert to shrink use an insert puller
77
insert puller
safest and easiest way to remove a valve seat insert
78
after installation of a valve seat insert you should check for
concentricity using a special concentricity gauge | runout should not exceed .002"
79
tools used for valve seat refinishing
valve seat grinding stones or cutters
80
when using valve seat grinder
mounted on holder and driven at high speeds by electric or air powered driver
81
valve seat cutters
usually turned by hand
82
valve seats can be reground for an interference fit by
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
interference fit of a valve face
will raise the initial seat pressure and promote quick seating will wear to full width in a short time after start up
84
when checking the valve face for proper seating
spread a light film of Prussian blue on the valve face and snap the valve face against the seat
85
regrinding a valve seat normally done in three stages to produce the proper profile
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
if a valve seat is to wide
it will lower seating force and cause carbon build up leakage and poor cooling
87
if a valve seat is to narrow
reduced contact area poor cooling and rapid wear
88
free length of a valve spring
is the free standing or uncompressed length of a spring
89
maximum allowable out of square on a valve spring
1/16" | springs with out of square will place side load on valves as they open and close
90
when testing spring tension
test under a specific load at a given height
91
low valve spring tension will cause
poor valve sealing poor valve cooling valve float or flutter
92
worn or damaged threads on a rocker arm
will make valve adjustments impossible or difficult
93
a cracked tubular pushrod that fills with oil will cause
greater mass and creates more valve train inertia
94
pushrods will bend under normal loads and return to normal a permanently bent rod can be the result of
fatigue mechanical failure service problem
95
basic check for push rod runout
roll along a flat surface
96
after installing valve springs
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
when pressure testing valves before installation
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
make sure to adjust vale bridges before valve clearance because
movement of the crosshead or bridge adjusting screw will the change valve clearance
99
excessive valve clearance can cause
poor engine performance and noisy valve train
100
insufficient valve clearance can cause
poor engine performance or damage to valve train components

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