US2109459A - Internal combustion engine - Google Patents

Description

March 1, 1938. F. c. BEST INTERNAL COMBUSTION ENGINE Filed June 15, 1935 2 Sheets-Sheet 1 March 1, 1938. F. c. BEST INTERNAL COMBUSTION ENGINE 2 shee cs-sneet 2 Filed June' 13, 1935 'llll Patented Mar. 1, 1938 Q INTERNAL COMBUSTION ENGINE Frank C. Best, Detroit, Mich asllgnor to Packon] Motor Car Company, Detroit, Mich a corporation of Michigan Application June is, 1935, Serial No. 26,484

9 Claims. (01. 122-90) This invention relates to improvements in the operating mechanism for the valves of internal combustion engines and is more particularly concerned with means for eliminating clearance and play in the mechanism in order to secure more efficient and quiet operation of the valves.

It has heretofore been proposed to employ take-up devices of the general character indicated, but such devices have not proven wholly satisfactory from a practical standpoint. Thus it is essential for satisfactory performance that such devices be capable of functioning properly over the extreme range of temperature estabwithstanding the stresses resulting from high frequency impulses to which they are subjected when employed with modern high speed engines, and that they shall be of su'fliciently small size and light weight to permit of use without adversely affecting the operation of conventional valve actuating mechanism or requiring material alteration of'the design of such mechanism.

It is proposed by the present invention to meet these various requirements and to provide a small and compact deviceiwhich is of light weight. and which will function, for an indefinite period without any attention, to automatically'regulate or eliminate clearance in the valve mechanism. In its more specific aspect the invention is concerned with the provision of a valve tappet which may be readily employed as a substitute for valve tappets or cam followers now commonly interposed between the cam shaft and the valve stem of poppet valves. It is a feature of the invention that the device, whether intended for use as a tappet or for association in some other way with conventional valve mechanism, may be readily assembled and sold as a complete unit.

It is a further object of the invention to provide a device of the character described in which a liquid medium is employed to oppose displacement of the working parts except when necessary for the purpose of taking up clearance in the valve mechanism, the construction preferably being such'that the liquid may, completely fill and be sealed within a closed fluid system, air being thus permanently excluded from the system so as to ensure uniformity of action.

It is a further object of the invention to provide a valve tappet which is preferably generally cylindrical in shape and of a length and diameter comparable to that of known nonadjustable or manually adjustable tappets, the working parts of the tappet being so arranged as lished in actual use, that they be capable of to occupy a portion only of the length of the tappet, whereby a roller or other anti-friction means for engagement with the operating cam may be utilized if desired.

A further object of the invention is to promote uniformity of action in devices of the character described by the provision of cooling means, whereby the plurality of devices required for the several valves of the engine may be maintained at substantially the same temperature.

The invention further contemplates an im-v proved method of assembling a clearance takeup device of the type employing a non-compressible fluid or liquid, whereby air may be discharged and the introduction of air into the fluid system permanently and completely eliminated. The method of assembly is preferably such that an initial compensation for variation in spacing between the valve stemsand the valve cams of internal combustion engines may be effected and precise similarity of function of the devices used with a plurality of valves may be'thus ensured.

Further objects and features of the invention will be apparent from the following description taken in connection with the accompanying drawings, in which Figure 1 is a sectional view through a portion of the valve mechanism of an engine illustrating the application of the invention to a valve tappet;

Figure 2 is a view partly in section of a por-- tion of the structure shown in Figure 1 taken at right angles to that figure;

Figure 3 is a side elevation of an internal combustion engine illustrating the application of a cooling system to the valve tappets;

Figure 4 is a sectionalview of a valve tappet illustrating a modified construction;

Figures 5 and 6 are sectional .and part-sectional views respectively illustrating alternative forms of a further modification; and

Figure 7 is a sectional view of a portion of a valve tappet illustrating a further modification.

In describing the invention reference is made to the preferred forms thereof illustrated in the accompanying drawings and specific language is employed. It will nevertheless be understood that no limitation of the scope of the invention is thereby-intended and that various further modi-' fications and alterations of the illustrated structure are contemplated.

In the arrangement shown in Figure lot the drawings, it will be observed that the valve stem is indicated at I2, the stem being provided with the usual spring seat i3 against which abuts the lower end of a coil spring l4, the latter serving to retain the head of the valve (not shown) on the valve seat in the conventional manner. The valve is reciprocated on rotation of the cam shait I which is provided with a radial cam i1, thrust being transmitted from the cam to the valve stem by means of a cam follower or tappet indicated generally at 23, the tappet being supported for reciprocating movement in a guide opening is formed in the stationary member 2|, the latter preferably constituting a part of the engine block. It will be appreciated that the structure thus far described is quite conventional and 'may assume other forms, the novel features of this embodiment of the invention residing in the construction of the valve tappet 20.

This valve tappet is shown as comprising a generally cylindrical casing 24, which slidably engages the walls of the opening is and which is preferably retained against rotative movement by means of a lug 25 which may be formed integrally with the casing 24 and which is received within the laterally extending slotted portion 26 of the member 2i. The structure whereby adjustment of the tappet to take up clearance is automatically efiected is located in what may be described for convenience as the upper portion of the casing 24, and thus the casing may be provided with an anti-friction device for engaging the radial cam i1 without increasing the conventional length of the tappet and consequently without redesigning to alter the spacing between the cam shaft and the valves ordinarily employed -in internal combustion engines.

This anti-friction means may take the form of a roller 28 provided with a bushing 29 which is journalled for rotation on a pin 30, the latter being secured in position in the lower end 3! of the casing 24 which is reduced in width for the purpose of more readily accommodating the roller.

Clearance in the valve actuating mechanism is eliminated by means which provides for automatically increasing the eilfective length of the valve tappet 20, and in the form of the invention shown in Figure 1 this means is located wholly within the upper end of the casing 24. Thus a cylinder 33 having a diameter substantially smaller than the internal diameter of the casing 24 is provided with a base portion 34, the latter being received within the cylinder and seating on an annular abutment formed within the casing. A piston 38 slides within the cylinder 33 and at its upper end carries and is preferably formed integrally with a valve stem engaging member 38, the latter having a sliding flt within the casing 24 and being retained therein by means of an expansion ring 33 or the like which seats in a groove formed internally of and at the upper end of the casing. The member 38 is provided with an upwardly directed, centrally disposed boss for engaging the lower end of the valve stem l2.

A coil spring surrounds the cylinder 33 and acts between the member 38 and the base 34 of the cylinder, thus serving to retain the cylinder in position within the casing and in engagement with the abutments 35 and also to urge the member 38 and piston 38 upwardly, or outwardly of the cylinder 33 to thereby expand the tappet. An annular flexible element, preferably in the form of a metallicbellows 43, surrounds the cylinder 33 and spring 42 and is secured at its upper and lower ends respectively to the member 38 and the base 34 of the cylinder 33. The manner in which the bellows 43 may be secured in position may vary, it being necessary, however, to provide a fluid-tight seal. Welding or soldering may be resorted to for this purpose.

A valve plate 48 is disposed within the cylinder 33 and is arranged to cooperate with the lower end of the piston 38 to close a passage 48 formed in the latter, a coil spring 48 being positioned in the lower end of the cylinder 33 to normally hold the valve plate 48 in seated position. Obviously this arrangement constitutes a simple form of one-way valve permitting fluid flow into but not out of the lower end of the cylinder 33, and other types of one-way valves may be employed in lieu of that shown. The passage 46 communicates through ports 49 formed in the lateral walls of the piston 38 with the reservoir defined by the interior of the bellows 43, the member 38, and the base 34 of the cylinder 33, this reservoir being designated by the numeral 50.

The base 34 of the cylinder is provided with a transversely extending passage 5| and axially directed passages 52 and 53 intersecting the passage 5l, the passage 82 communicating with the interior of the cylinder 33 and the passage 53 communicating with the reservoir 50. A tapered pin 54 may be driven into the passage 5i to close oil? the passages 52 .and 53 and complete the'sealing of the reservoir 50 and the parts with which this reservoir is in communication.

The piston 36 preferably fits somewhat loosely within the cylinder 33; at least there is sufiicient play to permit of seepage of liquid past the piston. Alternatively, a restricted by-pass may be provided to permit slow discharge of liquid from the closed end of the cylinder 33 into the reservoir 50. This is essential in order that expansion of liquid within the cylinder may be permitted without consequent upward movement of the piston as the temperature of the engine and associated parts increases during operation.

Preferably the boss 40 on the member 38 is dimensioned to receive a cup-shaped retainer 56 beneath which may be positioned one or more shims 51, the retainer 58 directly engaging the lower end of the valve stem. Thus with the parts in the position indicated in Figure 1 of the drawings, the upward thrust imparted by the cam I! to the roller 28 on rotation of the cam shaft will be transmitted through the tappet 20 to the valve stem i2 for the purpose of periodically raising the valve from its seat.

Assuming that the reservoir 50 and the interior of the cylinder 33 are completely filled with liquid, the spring 42 urges the member 38 outwardly and maintains the retainer 56 in engagement with the valve stem. Owing to the incompressibility of the liquid, the piston 38 will be prevented from moving downwardly within the cylinder 33, at least during the short period of time during which an impulse is actually applied to the tappet by the cam l1, and the tappet will function as a rigid unit to transmit thrust to the valve stem i2. As the engine heats up during the initial period of operation, the liquid within the closed end of the cylinder 33 will expand and will seep out into the reservoir past the piston 38 and through the ports 49. Expansion of liquid within the reservoir 50 is of course permitted by the flexible bellows 43 which is deformed to the extent required to accommodate the increased volume of liquid which is present at the higher temperature.

As the moving parts of the valve operating 7 2,109,469 mechanism wear, ordinarily tending to develop play and clearance between the tappet and the valve stem l2, the spring 42 forces the member 38 and piston 36 further outward to prevent the establishment of any clearance, flow of liquid past the valve 45 into the closed end of the cylinder 33 being permitted during this adjustment of the parts.

It is essential that the parts be assembled in such manner as to exclude air from the reservoir 50 and other liquid filled portions of the device. Obviously if air enters the closed end of the cylinder 33, even in extremely small quantity, downward movement of the piston 36 accompanied by compression .of this air is likely to occur on the transmission of thrust through the tappet, thus defeating the purpose of the fluid system. If air is present at any point in the fluid system, for instance in the reservoir 56, it is likely that an emulsion of air and liquid will form which will result eventually in the introduction of air into the closed end of the cylinder 33 in the form of minute bubbles. 'The preferred method of assembly whereby these difiiculties are avoided is substantially as follows.

The valve plate 45 and the spring 46 are first assembled in the lower end of the cylinder 33 and the spring 42 is assembled about the cylinder. The piston 36 is then introduced in the cylinder and the bellows 43 is secured to the member 38 and to the-base 34 of the piston to completely enclose the reservoir 56. The passages 5|, 52, and 53 are open so that a suitable liquid, for instance oil, glycerin, or the like, can be introduced in the passage 53, pressure being applied if necessary to open the valve 45, and when the reservoir 50, the passage 46, and the closed end of the'cylinder 33 have been completely filled with liquid, excess liquid will flow out of the passage 52, the air having all been discharged through this passage since there are no pockets within the system which might permit trapping of air. The pin 54 is now inserted to close the passages 52 and 53,

. engaging the valve seat.

the assembled piston and cylinder are placed within the casing 24, and the locking ring 39 is seated in the upper end of the casing. It will now be observed that the axial movement of the piston is definitely limited in either direction and the assembled device constitutes a self-contained unit which is in readiness for insertion as such in the tappet guide opening l9. While the dimensions of the casing 24 and the over-all length of the entire tappet are comparable to the dimensions of non-adjustable tappets, so that the present unit may be employed as a replacement unit without redesign of conventional valve actuating mechanism, the length of the tappet as measured between the cam engaging portion of the roller 28 and the remote end of the boss 40 when the member 38 is in engagement with the locking ring 39 is preferably less than the spacing between the lower end of the valve stem [2 and thedwell portion of the cam IT. The retainer 56 is then applied to the boss 40, a sufficient number of shims 51 being placed beneath the retainer, as determined by actual measurement, to depress the piston 36 to the extent necessary to provide a small clearance, say about .002 inch, between the member 38 and the locking ring 39 when the tappet is in assembled position with the engine valve It will be observed that by following this procedure, substantially the same degree of compression willbe applied to each ofthe springs 42 of the several tappets employed in a given engine regardless of variation in dimensions of the valve actuating mechanism resulting from conventional manufacturing tolerances. Thus uniformity of action of the several valve tappets is secured and each tappet is capable of expanding to the extent which will be required during the normal life of the engine. It

is of course obvious that if excessive wear takes place, further adjustment can ,be made by the introduction of additional shims 61 under the retainer 56, the retainer and the shims constituting in effect a manually adjustable device which may be regulated wholly independently of the automatic adjustment and which may therefore be substituted by other types of manually adjustable devices, for instance the more conventional threaded element commonly employed in manually adjustable tappets.

While care is preferably taken in the construction of the tappet to ensure that operation of the valve mechanism will not be aflected adversely by variation in'engine temperature, it may be advisable to providefor the cooling of the tappet guides so that several tappetsof an engine may.

53 for water leading from and communicating with the interior of the engine water pump '60, this passage extending rearwardly through the engine block and upwardly at the rear end thereof and passing forwardly in the tappet supporting. member 2|, being in communication with the water jackets 6| surrounding each of the tappet guides l9 and discharging at the forward end of the cylinder block into the engine cooling system. Obviously the details of this cooling arrangement may be varied to a considerable extent to suit the engine structure to which it is applied and to secure efficient circulation of cooling water about the tappet guides.

While Figure 4 illustrates a modified form of the arrangement shown in Figures 1 and 2, the construction is in general quite similar. Thus the tappet 20' comprises a casing 24 carrying a cam engaging roller 28', the moving parts of the tappet being located in the upper end of the easing.' These moving parts include a piston 36 which slides with a slight clearance in a cylinder 33', the piston being formed, at its upper end to provide an annular member 38 and an outwardly directed boss 40'. The piston 36*is urged outwardly of the cylinder by means of the coil spring 42, the spring being received within the piston. The valve plate 45' and the coil spring 48 which normally retains the valve in seated position against the passage 46 are also disposed within the piston, it being observed that the lower end of the cylinder is initially and completely closed piston and the flange 34"of the cylinder to seal the fluid system and to provide a reservoir 50'. A second flexible bellows 44 is secured to the lower side of the cylinder flange 34', the lower end of communicates with the valve controlled passage 46' through a transverse passage 49' in the upper end of the piston, and initial access to the valve controlled passage is also aflforded by a passage 62 extending through the boss 40' and bya passage 63 extending through the member 38'. Passages 62 and 63 are closed after the filling of the fluid system by plugs 65 and 66 respectively. A locking ring 39' provided in the upper end of the casing 24' retains the moving parts of the tappet in assembled position within the casing.

In operation this form of tappet is quitesimilar to that first described and is quite compact both axially and radially so as to permit of the use of the casing 24' having dimensions comparable with those of conventional manually adjustable tappets. The fluid system is filled with liquid through the passage 62, flowing downwardly into the cylinder past the valve plate 45' and through the ports 58 into the reservoir 55, air being discharged through the passage 63. When the system is completely filled, the plugs 65 and 66 are forced in to seal the system.

The flexible bellows 44 is readily extensible in an axial direction to accommodate expansion of fluid within the system as the engine temperature increases. The bellows 43 functions principally to permit inward and outward movement of the piston 36' and associated parts, lateral expansion of the bellows 43 in response to increased temperature being thereby rendered unnecessary with resultant avoidance of application of unnecessary stress to either bellows, increased uniformity of action resulting.

In the modified form of the invention shown in Figures 5 and 6 of the drawings, a general radially disposed flexible element 68 is employed, this element being preferably constructed in the form of a metallic disk having annular corrugations so as to permit of slight axial flexure to accommodate the increased volume of liquid resulting from increased temperature. The construction is otherwise quite similar to that il lustrated in Figures 1, 2, and 4, with the exception that the casing 24" and the cylinder 33" are preferably formed integrally. At its upper end the casing is provided with an annular flange 69 on which is seated and secured, in such manner as to' form a fluid seal, an annular plate Ill. The diaphragm 68 is secured to the plate 10 by crimping over the latter, as indicated at 12, the inner circumference of the diaphragm being received in an annular slot 13 formed in the member 38" which is in turn formed integrally with the piston 35", pressure being applied axially of the member 38" to clamp the diaphragm 68 securely in the slot 13. The plate 10 is also formed with a plurality of inwardly directed lugs 15 which cooperate with an annular flange 16 formed on the member 38" to limit outward movement of the latter and of the piston 36". The coil spring 42" surrounds the cylinder and acts between the latter and the member 38" to normally urge the piston outwardly, and a oneway valve comprising a valve plate 45" and a spring 48" prevents flow of liquid out of the cylinder except to the extent that seepage is permitted past the piston as in the first described embodiments.

The casing 24" is provided with two passages 18 and 19 through which the system may be fllled with liquid and air completely discharged therefrom in a manner quite similar to that hereinbefore described, these passages being both closed after filling by the insertion of a plug in the pasage 19. Ports 49" formed in the piston 36" aiIord communication between the reservoir 50" and the interior of the cylinder past the valve plate 45".

For the purpose of reducing the weight of the tappet shown in Figure 5, the lower end of the casing 24" may be apertured as indicated at 82 and the casing may be provided with a closed end 83 for direct engagement with the cam shaft in the conventional manner. Since, however, the moving parts of the construction illustrated in Figure 5 including the fluid system are extremely compact in an axial direction, it is possible to employ anti-friction means for engaging the cam, and this alternative arrangement is illustrated in Figure 6 in which the roller 28" is shown as mounted in a manner similar to that described in connection with the other embodiments of the invention.

In Figure 7a furthermodiflcation is shown which is closely related to the form of the invention shown in Figure 1, similar reference characters being employed to designate similar elements with the exception of a bellows 85 and a coil spring 86. The bellows 85 in this view is ribbed helically rather than circumierentially and receives within the recesses thus provided the coil spring 86 which is of corresponding helix. With this construction it is possible to employ a. coil spring of greater diameter without increase in the diameter of the casing 24, the stress applied to the spring being thereby reduced with resultant increase in life.

It will be observed that with the exception oi. the modified form of the invention shown in Figure 5, the several constructions illustrated in the drawings involve the employment of a fluid system for expanding the tappet, this fluid system being independent of the outside cylindrical casing of the tappet. In other words, pressure developed within the fluid system is not transmitted directly to the walls of the tappet casing. This is an important feature since it is desirable to reduce the total weight of the tappet to a minimum and thus to avoid the employment of outer casing walls or substantial thickness. If a thin wall is employed and fluid pressure is applied to the wall,

the casing is likely to expand with the result that the tappet will seize in the guide opening l9. By constructing the fluid system as a unit separate from the outer casing of the tappet, thisexpansion and seizure is avoided and thin casing walls can nevertheless be employed.

In all of the forms of the invention hereinbefore described it is preferred that a separate manually adjustable device be associated with the tappet, and similar devices have been illustrated in the drawings, but it will be appreciated-that this feature may be discarded if desired and reliance placed solely on the automatically operating portion of the tappet to eliminate clearance in the valve actuating mechanism. It will also be obvious that while the construction of the working parts of the tappet is preferably such as to permit of the use of an anti-friction cam engaging roller together with means for preventing the tappet from rotating during operation, such a roller may be eliminated together with its attendant advantages and reliance be placed on the more conventional arrangement shown in Figure v 5 and employing a casing having a closed end.

The invention is of course useful as a take-up device for valve actuating mechanism whether embodied in a tappet or whether employed in some other relation to the mechanism. A fur 1, 2, and 4 in which an axially arranged bellows is connected between the cylinder and piston,

this bellows may be made sufliciently flexible and elastic so that when initially compressed axially during assembling, an outward thrust will be exerted on the piston suflicient'to ensure that clearance will be properly taken up. This feature is not claimed specifically herein but is dealt with more particularly in my copending application Serial No. 26,483, filed June 13, 1935.

Having thus described the invention, what is claimed as new and desired to be secured by Letters Patent is:

1. A valve tappet operable automatically to take up clearance comprising a generally cylindrical casing, a cam engaging roller, means supporting said roller for rotation on the axis thereof in one end of said casing, and means carried by the other end of said casing for transmitting thrust to a poppet valve, said last named means including a valve stem engaging member supported within said casing for sliding movement in an axial direction, a cylinder mounted in fixed position in said casing and having one closed end, a piston carried by said member and movable in said cylinder, said piston and cylinder being constructed to provide a restricted fluid passage from one side to the other side of said piston, one-way valve means permitting fluid flow into said cylinder only, spring means urging said piston and member outwardly of said cylinder and away from said roller, means acting between said casing and member to limit outward movement of the latter, and means including a flexible diaphragm acting in conjunction with said cylinder and said member to provide a sealed reservoir completely filled with liquid and communicating with the open end of the cylinder, said flexible diaphragm yielding to compensate for expansion of fluid and to permit outward movement of said member to eliminate clearance between said member and valve stem.

2. In valve operating mechanism, the combination with a valve tappet having a generally cylindrical casing, of means supporting said casing for reciprocation, guide means acting between said first named means and said casing to prevent rotation of the latter, a cam engaging roller, means supporting said roller for rotation on the axis t ereof in one end of said casing, and means carried by the other end of said casing for trans mitting thrust to a poppet valve, said last named means including a valve stem engaging member supported within said casing for sliding movement in an axial direction, a cylinder mounted in fixed position in said casing and having one closed end, a piston carried by said member and movable in said cylinder, said piston and cylinder being constructed to providea restricted fluid passage from one side to the other side of said piston, one-way valve means permitting fluid flow into said cylinder only, spring means urging said piston and member outwardly of said cylinder and away'from said roller,-means acting betweensaidcasing and member to limit outward movement of the latter, and means including a-flexible diaphragm acting in conjunction with said cylinder and said member to provide a. sealed reservoir completely fllled with liquid and communicating with the open-end of the cylinder, said flexible diaphragm yielding to compensate for expansion of fluid and to permit outward movement of said member to eliminate clearance between said member and valve stem.. I

.-3. A valve tappet operable automatically to take up clearance comprising a generally cylindrical casing, a cam engaging roller, means supporting said roller 'for rotation on the axis thereof in one end of said casing, and means carried by the other end of said casing for transmitting thrust to a poppet valve, said last named means including a valve stem engaging member supported within said casing for sliding movement in an axial direction, a cylinder mounted in fixed position in said casing and having one closed end,

a piston carried by saidmember and movable in said cylinder, said piston and cylinder being constructed to provide-a restricted fluid passage from one side to the other side of said piston, one-way valve means permitting fluid flow into said cylinder only, spring means urging said piston and member outwardly of said cylinder and away from said roller, means acting between said casing'and member tolimit outward movement of the latter, and meansincluding a flexible diaphragm of the metallic bellows type arranged generally coaxially of and about the cylinder and acting in conjunction with said cylinder and said member to provide a sealed reservoir completely filled with liquid and communicating with the open end of the cylinder, said flexible diaphragm yielding to compensate for expansion of fluid and to permit outward movement of said member to eliminate clearance between said member and valve stem..

4. A valve tappet operable automatically to take up clearance comprising a generally cylindrical casing, a cam engaging roller, means supporting said roller for rotation on the axis thereof in one end of said casing, and means carried by the other end of said casing for transmitting thrust to a poppet valve, said last named means including a valve stem engaging member supported within said casing for sliding movement in an axial direction, a cylinder mounted in fixed position in said casing and having one closed end, a piston carried by said member and movable in said cylinder, said piston and cylinder being constructed to provide a restricted fluid passage from one side to the other side of said piston, one-way valve means permitting fluid flow into said cylinder only, spring means urging said piston and member outwardly of said cylinder and away from said roller, meansacting between said casing and member to limit outward movement of the latter, and means including a flexible diaphragm formed as a metallic disk having annular corrugations and acting in conjunction with said cylinder and said member to provide a sealed reservoir completely filled with liquid and communicating with the open end or the cylinder,

acting yieldingly to lengthen the tappet, said elastic mean's being ineflective to oppose the seating of the valve by the valve spring, said elastic means being interposed between said casing and cylinder and surrounding the latter.

6. A valve tappet operable automatically to eliminate clearance in the valve actuating mechanism, said tappet comprising a casing having dimensions comparable to those of standard manually adjustable tappets, and means disposed withinsaid casing operable on, occurrence of clearance in the valve actuating mechanism to increase the effective length of the tappet, said means including a sealed fluid system completely fllled with liquid for resisting axial compression of said tappet and comprising a cylinder and pistcnlocated within said casing, and elastic means acting yieldingly to lengthen the tappet, said elastic means being ineflective to oppose the seating of the valve by the valve spring, said elastic means comprising acoil spring surrounding said cylinder and piston and acting between the latter to urge the piston outwardly.

'7. A valve tappet operable automatically to eliminate clearance in the valve actuating mechanism, said tappet comprising-a casing having dimensions comparable to those of standard manually adjustable tappets, and means associated with said casing operable on occurrence of clearance in the valve actuating mechanism to increase the, effective length of the tappet, said means including a sealed fluid system completely filled with liquid for resisting axial compression of said tappet and comprising a cylinder and, piston located within said casing, elastic means acting yieldingly to lengthen the tappet, said elastic means being ineffective to oppose the seating 01' the valve by the valve spring, said elastic means comprising a coil spring surrounding said cylinder and piston and acting between the latter to urge the piston outwardly, and expansiblesealing means comprising a bellows disposed within said casing and surrounding and secured at its ends to said piston and cylinder.

8. In an automatically expansible valve takeup device, the combination with a piston, of a unitary member affording a cylinder portion for the reception of said piston, said cylinder portion and piston constituting a part of a closed fluid system resisting compression of said device, elastic means acting between said member and said piston to yieldingly expand said device, means for completely sealing said system, and a generally cylindrical casing, said fluid system being housed within and readily removable as a unit from said casing without discharge of liquid from the system.

9. In an automatically expansible valve takeup device, the combination with a closed fluid system resisting compression of said device, of means acting to yieldingly expand said device, means for completely sealing said system, and a generally cylindrical casing, said fluid system being housed within and removable as a unit from said casing without discharge of liquid from the system.

FRANK C. BEST.

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