Method for forming valve seats

A method of forming cylinder heads having bonded valve seat inserts. The method reduces the machining operations necessary to place the insert in place by forming the cylinder head casting with reference surfaces that are employed for determining the pressing axis and location for the valve seat insert.

BACKGROUND OF THE INVENTION 
This invention relates to a valve seat arrangement for a reciprocating 
machine and more particularly to an improved method of forming a bonded 
valve seat for an internal combustion engine. 
In internal combustion engines, it frequently is the practice to employ 
aluminum or aluminum alloys as the material for a number of the major 
engine castings such as the cylinder heads. When the cylinder heads are 
formed from aluminum or aluminum alloys, however, certain components of 
the cylinder head are formed from a dissimilar material so as to improve 
performance. For example, the valve seats of the cylinder head are 
normally formed from a harder, less heat conductive material such as iron 
or ferrous iron alloys. By utilizing such harder materials, the valve seat 
life can be extended. However, the attachment of the dissimilar valve seat 
insert into the cylinder head presents a number of problems. 
Conventionally, it has been the practice to form the cylinder head passages 
with recesses adjacent the seating area into which the insert rings which 
form the valve seat are press fit. The use of press fitting has a number 
of disadvantages. These disadvantages may be understood by reference to 
FIG. 1 which shows a conventional pressed in type of valve seat. 
The cylinder head material 21 is formed with a counter-bore 22 at the 
cylinder head recess side of the flow passage 23. The flow passage 23 may 
be either an intake passage or an exhaust passage. The insert ring is 
indicated by the reference numeral 24 and may be formed from any suitable 
material, such as a Sintered ferrous material. Such materials have the 
advantage of having high wear capabilities. After the insert 24 has been 
pressed into place, its surface is machined as at 25 so as to form the 
actual valve seating surface. 
As may be seen, this technique requires relatively large valve seat inserts 
in order to withstand the pressing pressures. In addition, the press fit 
must be such that the insert ring will not fall out when the engine is 
running. As a result, there are quite high stresses exerted both on the 
cylinder head and on the insert ring. The stresses can result in loads 
which may eventually cause cracks in the cylinder head. 
These types of construction also limit the maximum size and spacing of the 
valve seats in order to ensure adequate cylinder head material between 
adjacent valve seats to reduce the likelihood of cracking. In addition, 
the large seats compromise the configuration of the intake passages, 
particularly at the critical valve seating area. Finally, these 
constructions result in somewhat poor heat transfer from the valve to the 
cylinder head due to the poor thermal conductivity of the valve seat 
material and the poor contact area between the insert 24 and the cylinder 
head 21. 
In addition, the interface between the insert ring and the cylinder head 
frequently leaves voids or air gaps which further reduce the heat transfer 
and thus cause the valves to run at a higher temperature. This higher 
temperature operation of the valves requires the valves to be made heavier 
and stronger and thus reduce the performance of the engine and increase 
its size and costs. 
Many of these problems become worse as the engine reaches operating or 
higher temperatures. Because of the higher coefficient of expansion of the 
cylinder head material, the press fit force diminishes and the contact 
area for heat transfer also decreases. 
In addition to these problems which deal primarily with the ultimate 
performance of the resulting cylinder head and associated engine, there 
are certain additional manufacturing disadvantages with the pressed-in 
type of insert. These have to do with the cost and the complicated 
manufacturing process by which the pressed-in inserts are formed. 
As has been previously noted, the insert ring is press-fit into a bore or 
counterbore 22 which is machined on the cylinder head recess side of the 
flow passage 23. Because of the techniques which are employed, the 
positioning and formation of this bore must be done very accurately so as 
to ensure that the resulting valve seat will be appropriately positioned 
so that it will cooperate with the associated poppet valve. Thus, a 
machining operation has been required to accurately form the valve seat 
receiving counterbore 22. In addition and frequently at the same time, the 
bore in the cylinder head which receives the respective valve guide also 
is machined. 
Furthermore, to accommodate both the pressing of the valve seat insert and 
of the valve guide, separate heating steps are required for heating the 
cylinder head and/or cooling the valve seat insert and the valve guide so 
as to facilitate installation. 
The machining operations require a cleaning operation before the subsequent 
heating so as to ensure that particles will not be present in the cylinder 
head that can interfere with the subsequent press-fitting. Thus, the prior 
art methods are not only expensive but also time-consuming. In addition to 
resulting in a cylinder head that has less than optimum performance. 
To overcome the disadvantages in the performance of the cylinder heads 
having pressed in inserts it has been proposed, therefore, to employ a 
technique wherein the insert ring is metallurgically bonded but not 
alloyed to the cylinder head material. This is accomplished by pressing 
the insert into place and passing an electrical current through the insert 
which is sufficient to cause the cylinder head material to plastically 
deform upon insertion of the insert ring. The plastically deformed phase 
of the cylinder head material forms a metallurgical bond at the interface 
with the insert ring without any significant resulting alloying of the 
cylinder head material to that of the insert ring. Such an arrangement is 
disclosed in our copending application entitled, "Valve Seat Bonded 
Cylinder Head and Method for Producing Same," application Ser. No., 
08/483,246, filed Jun. 7, 1995 and assigned to the assignee hereof. In 
addition, certain of these techniques are also described in our copending 
application entitled "VALVE SEAT," application Ser. No. 08/278,026, filed 
Jul. 20, 1994, in our names and also assigned to the Assignee hereof. 
These techniques have a number of advantages over the conventional 
structures. First, they permit the use of much smaller insert rings since 
the pressing pressure is reduced and thus the shape of the intake passage, 
particularly the shape of the cylinder head passages, particularly in the 
critical area of the valve seats are not compromised. In addition, the 
bond strength is considerably higher than more conventional methods. 
Furthermore, this technique, because of the improved way in which the 
adhesion is formed, permits the use of much smaller insert rings and thus 
permits the valve seat openings to be positioned closer to each other 
without the likelihood of causing defects in the cylinder head which may 
manifest themselves during the engine running and life. 
Therefore it is an object of this invention to provide a further improved 
method for bonding such valve seat inserts into place. 
It is a further object of this invention to provide a further improved 
method for bonding such valve seat inserts into place that minimizes the 
machining and other steps required to form the valve seat. 
SUMMARY OF THE INVENTION 
This invention is adapted to be embodied in a method of forming a valve 
seat for a cylinder head having a flow passage ending in a combustion 
chamber recess. The method comprising the steps of casting a cylinder head 
having a flow passage. The cast cylinder head is formed with reference 
surfaces used to establish three mutually perpendicular reference axes 
that intersect at a common point. A recess is formed at the combustion 
chamber side of the flow passage. An insert is formed to be received in 
the recess. The insert has an opening adapted to form a flow opening 
registering with the cylinder head flow passage and an outer surface 
positioned to engage the part of the cylinder head defining the recess. 
The insert is then placed in alignment with the recess. Pressure is then 
applied to the cylinder head and the insert along an axis defined by the 
reference axes. An electrical current is passed through the insert and the 
cylinder head during at least a portion of the pressing operation to heat 
the cylinder head and form a metallurgical bond between the cylinder head 
and the insert.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
It should be noted that the actual mechanical way in which the bond is 
formed with the valve seat is as described in the aforenoted co-pending 
applications, the disclosures of which are incorporated herein by 
reference. Even though these disclosures are incorporated herein by 
reference and the invention in this application deals primarily with the 
pressing method, a general description of the bonding process will also be 
included. However, where further information is required, reference may be 
had to the aforenoted co-pending applications. 
Referring first to FIG. 2, a cylinder head for an internal combustion 
engine utilizing the invention is identified generally by the reference 
numeral 31. The cylinder head includes a base cylinder head casting 32 
which is formed from an aluminum or aluminum alloy. Such materials are 
highly desirable for use in engine components and particularly cylinder 
heads because of their light weight and high thermal conductivity and 
specific, preferred materials will be disclosed later herein. 
The cylinder head 32 as cast is formed with combustion chamber recesses 33 
which cooperate with the associated cylinder bore and piston (both of 
which are not shown) of the associated engine to form its combustion 
chambers. An intake charge is delivered to these combustion chambers 
through one or more intake passages 34 that are formed in the cylinder 
head material 32 and which terminate at valve seat 35 within the cylinder 
head recess 33. Poppet type intake valves 36 are supported within the 
cylinder head 32 by valve guides 37 for controlling the opening and 
closing of the valve seats 35 in a well known manner. The intake valves 36 
may be operated by any known type of valve actuating mechanism. 
One or more exhaust passages 38 extend from the cylinder head recesses 33 
and specifically from valve seats 39 formed therein for the discharge of 
the combustion products from the combustion recesses 33 in a manner also 
well known in this art. Exhaust valves 41 are slidably supported in the 
cylinder head 32 by valve guides 42. These exhaust valves 41, like the 
intake valves 36 are operated by any known type of mechanism. 
When the cylinder head casting is initially made the recesses for the 
insert rings, which will be described, and which ultimately form the valve 
seats 35 and 39 are as will be described. In addition, the combustion 
chamber recesses 33 and other surfaces such as the lower surface of the 
cam chamber in which the valve operating cam shafts (not shown) are formed 
so as to provide reference surfaces. These reference surfaces are employed 
so as to define three mutually perpendicular intersecting reference axes 
which may be considered to be the X, Y and Z axes for determining the 
pressing direction and insert location for forming the valve seats 35 and 
39, as will become apparent. 
The invention, as should be readily apparent from the foregoing 
description, deals in the method in which the valve seats 35 and 39 are 
formed and the apparatus for performing this method. This apparatus is 
shown best in FIGS. 3-5 and will be discussed and described by reference 
to these figures. 
The apparatus is indicated generally by the reference numeral 43 and may be 
considered to be similar to a pressure welding apparatus. However, and as 
will become apparent, the actual electrical current flow is not sufficient 
to cause any welding of the insert rings to the cylinder head material. 
The apparatus 43 is comprised of a press base 44 that has a support element 
45 on which a fixture 46 is mounted so as to accommodate a cylinder head 
32. The fixture 46 is disposed so that the cylinder head 32 will be held 
at an angle. This angle is such that one of bores 47 or 48 (FIG. 2) that 
received the valve guides 37 or 42 will be in line with the pressing axis 
of the equipment. The actual axis of the pressing direction is determined 
by the aforedescribed reference axes defined by the cylinder head casting 
as also described. 
Supported above the table or base 45 is a ram 49 which is driven by a 
hydraulic or pneumatic motor 51. The ram 49 carries a pressing electrode 
member, indicated generally by the reference numeral 52. 
Affixed to the pressing electrode member 52 is an adjustable post 53 which 
cooperates with a proximity sensor or detector 54 such as a laser which is 
utilized to determine the degree of movement during the pressing of the 
inserts in place and the degree of movement of the ram 49 specifically. 
The output of this detector 54 indicates the depth at which the insert is 
pressed into the cylinder head, as will become apparent. 
The base 44 carries a source of high energy electricity that is transmitted 
to the base plate 45 through a first conductor 55 and to the pressing 
member 52 through a second conductor 56. The conductors 55 and 56 will 
accommodate vertical movement and the conductor 56 is so configured in 
this embodiment. The pressing electrode 52 is preferably charged 
positively and the support base 45 is negatively charged. 
The actual pressing apparatus and its association with the cylinder head 
will now be described by reference FIG. 5. As seen in this figure, a 
mandrel post, indicated generally by the reference numeral 57, is placed 
into the valve guide opening 47 of the cylinder head 32. The mandrel post 
57 is formed from a central post part 58 that is formed from a suitable 
material, such as a metallic rod. However, in order to provide electrical 
insulation, for a reason which will become apparent, the rod 58 is 
provided with an insulating coating 59. Although the insulating coating 59 
may be of any material, a ceramic material, such as alumina, is preferred. 
The alumina coating 59 is flame sprayed onto the rod base 58 and then is 
finished by polishing. 
A stopper ring 60 is affixed to the mandrel 57 and contacts the inner 
surface of the cylinder head intake passage 34 around the valve guide 
opening 47 so as to limit how far the mandrel post 57 extends into the 
valve guide opening 47. 
A further pressing member, indicated generally by the reference numeral 61, 
is provided with an opening 62 complementary in shape to the mandrel and 
is slid thereover. The pressing member 61 has an actual pressing surface 
that is formed by a hardened body 63 formed from an appropriate material 
and which either is magnetized or which carries a magnetic body 64 so as 
to attract and hold an insert ring 65 thereupon. The body surface 63 is 
formed with a tapered end 66 that is complementary to the shape of the 
insert ring 65, as will be described later by reference to FIG. 6. Because 
the pressing body 61 is engaged the electrode 52, electrical current will 
flow through the pressing body 61 and through the insert ring 65. As will 
become apparent later, when the insert ring 65 is engaged with the 
cylinder head 32, an electrical path will be formed through the cylinder 
head and base 45 to the conductor 55 to complete the electrical path. The 
insulated coating 59 on the mandrel 57 prevents short-circuiting around 
this area. 
The construction of the insert ring 65, its shape and the shape of a 
cooperating recess 67 formed in the cylinder head at the mouth of the 
intake passage 34 will now be described by primary reference initially to 
FIG. 6. FIG. 6 is an enlarged crosssectional view of one of the intake 
valve seats 35 and this description may be considered to be typical for 
that which may be utilized with the exhaust valves 41 to form the exhaust 
valve seats 39. 
Basically, the valve seat 35 is formed by the insert ring, indicated by the 
reference numeral 64 and which has a metallurgical construction as will be 
described. This insert ring 64 is bonded to the cylinder head material 32 
by a relatively thin metallurgical bonding layer that is formed in a 
manner which will be described. Adjacent this bonding layer, there is 
formed a portion of the material of the cylinder head 32 which has been 
plastically deformed. It should be noted that the alloy of the cylinder 
head 32 is of the same chemical composition and same physical structure, 
except for being slightly work hardened in the area adjacent the bonding 
layer, as in the remainder of the cylinder head material 32. 
The insert ring 64, is formed from a Sintered ferrous alloy base 67 having 
a coating material filled within its intercices and also on its external 
surface as desired, which coating is indicated at 68. This material is 
preferably formed from a good electrical conductor such as copper. Copper 
also has another useful function as a coating for a reason to be 
described. 
The insert ring 64 in accordance with this embodiment is formed with a 
cylindrical inner surface 69 that is relatively short in axial length and 
which merges into a tapered conical surface 71 which extends for a 
substantially length. The surface 71, which is actually the pressing 
surface, as will be described, ends in an end surface 72. 
A first, conical outer surface section 73 extends at an acute angle to the 
axis of the cylindrical section 69 and merges at a rounded section 74 into 
an inclined lower end surface 75 which is formed at a greater angle than 
that of the conical surface 73. However, this angle is still an acute 
angle to a plane perpendicular to the axis of the cylindrical section 69. 
The cylinder head material 32, preferably as cast, is formed with a recess 
that is comprised of a first section 76 that is connected to a second 
section 77 that are joined by a horizontal surface that forms a projecting 
ledge 78 that contacts the rounded portion 74 of the insert ring 64 upon 
initial installation (FIG. 6). This tends to form a localized area that 
will begin the plastic deformation phase. 
It has been noted that the copper coating serves the function of improving 
the electrical conductivity of the insert ring 64. Also, it has been noted 
that the copper performs additional functions. As should be apparent from 
the foregoing description, it is important that the bonding process not 
result in any alloying of the insert ring material and specifically that 
of the base 67 with the base material of the cylinder head 32. 
The copper also serves the function of forming a eutectic alloy with the 
material of the cylinder head 32 which eutectic alloy has a lower melting 
point than either the melting point of the copper or that of the cylinder 
head material. As a result, the plastic deformation is accomplished with 
added ease and the metal can flow out during the pressing process as will 
be noted without large heat generation. In addition, the copper will react 
with any aluminum oxides that may be present on the surface of the recess 
66 of the cylinder head 32 so as to extrude these oxides and provide a 
purer finish. 
Preferably, the copper plating is done by electroplating and has a 
thickness in the range of 0.1-30 .mu.m. Also, the cylinder head material 
of the body 32 is preferably an aluminum alloy as set forth in Japanese 
Industrial Standard (JIS) AC4C. Also the AC4B and AC2B aluminum alloys or 
other light alloys may be utilized. 
Beginning now to describe the pressing operation by reference to FIGS. 
6-10. FIG. 6 shows the conditions comparable to that in FIG. 5. The 
pressing force is then applied by actuating the hydraulic ram operating 
motor 51 so as to move the electrode 52 into contact with the pressing 
mandrel electrode 59. Prior to this the mandrel 59 may be rotated to 
ensure that the insert ring 64 is correctly seated. 
A pressing force is then applied at a force indicated at the force P1 in 
FIG. 11. This force acts along an axis defined as noted based upon the 
three reference axes determined from the reference surfaces of the 
cylinder head casting. This pressing axis will be coincident with the 
final axis of the seat. Pressure is maintained up until the time T1 
wherein an electric current flow through the joint is initiated. When this 
occurs, there will be a high electrical resistance due to the small 
contact area and a plastic deformation begins in the range indicated at A 
in FIG. 7 so as to displace the material of the cylinder head 32. 
As the current is built up, the material will reach a temperature wherein 
the internal resistance is high enough to cause the copper coating layer 
74 to defuse into the cylinder head material in the area 78 or shown in 
the range A so as to form the eutectic alloy that results in the area 
indicated at A in FIG. 7 and which eventually causes displacement and a 
plastic deformation and the valve seat 64 will begin to become embedded in 
the material of the cylinder head 32. 
The eutectic layer is displaced as indicated at B in FIG. 8 toward the area 
which will be removed from where the final valve seat will be formed. Said 
another way, this material will be later machined away. 
The actual deformation of the insert into the cylinder head body, as 
measured by the sensor 54, begins at the point in time T2. At some time 
thereafter, the electric current will have reached its maximum amount at 
the first level at the point T3 and then the pressing pressure is 
increased from the pressure P1 to a new higher pressure P2 which is then 
held. 
This plastic deformation then continues and after a certain deflection and 
at the time period T4, the electric current is reduced sharply toward zero 
as shown in FIG. 11. This is done to avoid overheating and to ensure that 
there will be no alloying of the insert ring material and that of the 
cylinder head material. There will, however be atomic diffusion of the 
materials in the area C. 
The electric current is then built up higher to a new level equal to or 
slightly higher than that before and is held at this level until the point 
in time T5. This pressing is continued after this still at the pressure P2 
during which time period the current flow is dropped back to zero at the 
time period T6 while pressing is continued. The final joint appears as 
shown in FIG. 9 and it will be seen that substantially all of the eutectic 
alloy has been pushed from the area between the insert base 67 and the 
base cylinder head material resulting in only the work hardened adjacent 
the joint and atomic bonding in the area C. In addition, the metallurgical 
bonding will be completed. 
During this time and after the completed bonding, the apparatus measures 
the amount of actual embedding of the insert ring 67 into the cylinder 
head 32. There is an allowable range as indicated by the dimension D in 
FIG. 11 which range is about 0.5 millimeters to 2 millimeters and 
preferably in the range of 1 to 11/2 millimeters. If the sinking level is 
not reached in this range, then it can be assumed that the joint is not 
satisfactory. This judgment may also be made during the actual pressing, 
bonding operation. If the deflection is not in the proper range, the 
process may be discontinued. 
In addition, a judgment may be made whether the main current values and 
total energization time are in the allowable range. If this is also met, 
then certain cylinder head valve seats may be actually pull testing to 
assure accuracy and satisfaction of the entire lot of cylinder head 
formed. 
The way this testing is done is that a tensile force is applied by putting 
an appropriate fixture under the projecting edge of the insert ring as 
shown in FIG. 9 and applying a pulling force. This way, the actual force 
necessary to separate the bonded joint can be measured. If the samples are 
within the predetermined range, then it can be assumed that all heads in 
the lot, which have also passed the other test, are satisfactory. 
In addition to these tests, there can be a heat endurance test and/or heat 
shock test applied to the finished cylinder head. All of these things are 
done before the final machining. 
The heat endurance test is performed on the cylinder head in the state 
shown in FIG. 9. The head is kept in a furnace at 300.degree. C. and 
atmospheric pressure in the range of 24 to 200 hours. A further pulling 
test is then performed and the area inspected for separation or cracks. In 
a heat shock test, the finished cylinder head in the condition shown in 
FIG. 9 is heated to 300.degree. C. in a furnace at that temperature and 
atmospheric conditions. The thus heated head is then immediately immersed 
in ice water at 0.degree. C. This procedure is repeated ten times and then 
the cylinder head is checked for separation and cracks and the separation 
test aforenoted is performed. 
Assuming that the tests indicate that the head lot is satisfactory, then 
the heads are finish machined by grinding or the like to the conditions 
shown in FIG. 10. Thus, it will be seen that all of the eutectic alloy 
phase B is removed and only the metallurgical bonding area C remains. The 
finished joint has no melt reaction layer or no actual alloying between 
the cylinder head material and that of the insert ring. 
A visual inspection is also made after the bonding is completed. In this 
inspection it is checked to see that the eutectic alloy portion B (FIG. 9) 
extends around the entire insert without voids. If not the piece should be 
rejected as the bond may have voids. 
FIG. 12 shows another embodiment of the invention and in this embodiment 
the electrode 52 of the pressing head is provided with a ferrous 
semi-circular shield 101 which functions to provide a magnetic flux in the 
magnetic field which directs the eutectic alloy that is removed from the 
bonded area. This can be done so as to ensure that more of the eutectic 
alloy is disposed in the area where the most machining will occur so as to 
minimize the amount of machining necessary. Also this is done to insure 
complete bonding around the joint. 
The actual process by which the axis of the pressing force is operated and 
certain alternative pressing methods will be described by first reference 
to FIG. 13. At the step S1, the cast working reference planes of the 
cylinder head are utilized to define the aforenoted reference axes. From 
these axes are located the desired axis of the cylinder head recess that 
will receive the individual valve seat and also the axis location of the 
valve guide opening 47 which is, in accordance with a preferred embodiment 
of the invention, coaxial with the cylinder head recess. The axis of 
pressing is also determined in this same manner. 
Then, at the step S2 the valve seat insert receiving recess is machined and 
at the step S3 the cylinder head valve guide opening 47 is machined. 
Although these machining steps are described as separate steps, the 
machining may be performed at substantially the same time by a single 
compound tool. 
The valve seat insert ring 64 is then placed in position at the step S4, 
this being the position described in conjunction with FIGS. 5 and 6 
previously. 
If desired, a washing step may precede this at the step S5 although this is 
alternative. This washing may either be done with a fluid or a merely an 
air pressure cleaning. 
At the completion of step S4, the pressing operation previously described 
in conjunction with FIGS. 6-9 is performed in the manner then described. 
Subsequently at the step S7, the actual valve guide is press-fit into 
position. In order to assist the press-fitting, either the cylinder head 
may be preheated and/or the valve guide may be chilled as seen at the step 
S8. 
After the valve guide is pressed into position at the step S7, at the step 
S9 there is a rough machining of the valve seat and then at the step SiO 
there is the final machining of the valve seat surface. 
The program then moves on to succeeding processes such as the machining of 
the bearing surfaces for the cam shafts and other machining operations 
which may be required. 
FIG. 13 also shows an alternative method for bonding the valve seat inserts 
into place. This method involves the use of the valve guide itself as the 
support for the pressing mandrel. In accordance with this method, at the 
step S3 the program then may move to the desired washing step at S5 and 
subsequently the heating and/or cooling step at S8 may be employed so as 
to perform the pressing in of the valve guide at the step S7. 
Then, the program may move to the step S4 so as to position the valve seat 
insert and to the step S6 so as to press in the valve seat insert and 
achieve the bonding as previously described in conjunction with FIGS. 5-9. 
In the methods described in conjunction with FIG. 13, the actual pressing 
axis has been defined by the formation of the valve guide receiving recess 
47 in the cylinder head. However, the pressing axis may be defined by 
another bored or machined hole in the cylinder head and FIG. 14 shows such 
a method. 
In this method, the program again starts at the step S1 so as to define the 
reference axes. From these axes, then the valve seat receiving recess is 
machined at the step S2. A further machined hole in the cylinder head such 
as a knockout pin hole is formed at the step S20. From this step the 
program can then move to the step S4 so as to position the valve guide 
insert and to press and bond it into place at the step S6. As previously 
mentioned, if desired, a washing operation may precede this at the step 
S5. 
After the valve seat insert is bonded at the step S6, the program then 
moves to the step S3 so as to bore the final opening 47 to receive the 
valve guide. The valve guide is then pressed in place at the step S7. As 
previously described, the pressing in of the valve guide may be preceded 
by heating of the cylinder head and/or cooling of the valve guide at the 
step S8. 
Once the valve guide is positioned, then the rough machining steps S9 and 
final machining steps S10 for the valve seat surface may be performed. 
This routine shown in FIG. 14 may also employ an arrangement wherein the 
valve guide is pressed in place before the valve seat insert is pressed in 
place. This routine follows the alternate path also shown in FIG. 13. If 
this methodology is followed, then the valve guide receiving hole 47 of 
the cylinder head is machined at the step S3 after the completion of the 
boring of the knockout pin hole at step S20. The routine then continues 
through the alternate steps S5, S8, and the steps S7, S4, and S6 in that 
order as shown and described in conjunction with FIG. 13. Because of the 
fact that this method is the same as that described in conjunction with 
that figure, a further description of this embodiment is not believed to 
be necessary. 
In the embodiments thus far described, it has been assumed that the recess 
in the cylinder head to receive the inserts must be machined. In 
accordance with the methodology that is employed it may not be necessary 
to machine these recesses and thus further time and cost savings can be 
generated. This is primarily possible because of the fact that the 
pressing operation and the use of the mandrel can be employed in order to 
form the desired location for the valve seat insert rather than relying on 
the recess to perform this function, as in the prior art pressed in insert 
methods. 
Referring to this figure, the initial step indicated at S1a is performed 
which includes not only the casting of the working reference plane so as 
to define the reference axes but also to cast the desired valve seat 
recess configuration and location. Thus, after this is accomplished then 
at the step S4 the valve seat insert may be placed and subsequently 
pressed and bonded at the step S6 in the manner as previously noted. 
Then, the program moves to the step S3 so as to form, as by boring, the 
cylinder head recess 47 that will receive the valve guide. 
The valve guide is then pressed in place at the step S7 with, if desired, 
the preceding heating of the cylinder head and/or cooling of the insert at 
the step S8. 
The rough and finish machining of the valve seat insert are then performed 
at the steps S9 and S10, respectively. 
FIG. 16 shows another methodology by which the inserts may be bonded in 
place. This methodology follows generally the embodiments shown in FIG. 13 
and where that is the case the steps have been identified by the same 
reference numerals and will not be described again. However, in accordance 
with this embodiment, the valve seat insert receiving recess of the 
cylinder head is also not machined like the embodiment shown in FIG. 15. 
Thus the program begins at the step S1a wherein the reference surfaces and 
recess are formed in the cylinder head by casting. In this embodiment, 
however, like the embodiment of FIG. 13, the program the moves to the step 
S2 so as to bore the recess 47 in the cylinder head to receive the valve 
guide. 
The program then continues on with the steps as shown in FIG. 13 or the 
alternatives thereof. Therefore, these steps and their sequence will not 
be repeated again. 
FIG. 17 shows a routine which, like the embodiments of FIGS. 13 and 16 
begins at the step S1a so as to form as cast the cylinder head recess to 
receive the valve seat insert. However, this embodiment also employs the 
use of another hole in the cylinder head than the valve guide receiving 
hole for locating the components and thus follows the alternate control 
routine shown in FIG. 14 beginning with the step S20. Again, since the 
steps and their order follow from this point that of the embodiments shown 
in FIG. 14, this description will not be repeated. 
In the foregoing description, a specific shape of insert and cylinder head 
recess has been depicted and described. The insert and recess may take 
different configurations as shown in FIGS. 18-20. FIG. 18 shows a 
configuration similar to that of the previous embodiment, but the cylinder 
head recess is merely formed with a simple taper. In addition, the insert 
is not rounded, but the bonding operating will begin at a small area as in 
the previously described embodiment. 
FIG. 19 shows another embodiment using a different shape ring and that 
lends itself to what is called end pressing. However, the shape of the 
insert ring is again such that the initial deformation of the cylinder 
head will begin at the middle of its tapered area. In addition, an outer 
peripheral groove will assist in locating. 
FIG. 20 shows a simplified form of shape of insert ring that adapts itself 
to the pressing method which can be utilized with all of the embodiments 
of FIGS. 1-17. Again, however, the arrangement is designed so as to ensure 
localized initial deformation. Also, each of these embodiments are 
designed so as to provide the desired length of bonding surface to provide 
the desired bonding strength. Also, although a specific cylinder head 
material and insert material have been disclosed, various other materials 
may also be practiced. 
Thus, from the foregoing description it should be readily apparent that the 
described pressing and bonding methods provide very effective valve seats 
that will eliminate sacrifices in strength and port configuration over 
conventional methods. In addition the manufacturing process is simplified 
and the cost reduced. Furthermore because of better heat transfer, lighter 
weight valves can be utilized and larger valve areas can be employed so as 
to increase the performance of the engine without shortening its life. Of 
course, the foregoing description is that of the preferred embodiments of 
the invention, and various changes and modifications may be made without 
departing from the spirit and scope of the invention, as defined by the 
appended claims.