Abstract:
Valve clearance adjusting shims in an internal combustion engine having an overhead cam, are removed and replaced by compressing a valve spring through a cam follower forcibly held against the spring pressure by a valve clearance tool. A method for relieving pressure against the valve spring and for replacing the valve clearance adjusting shims is described.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to the art of adjusting valve clearances in an overhead cam internal combustion engine, and more particularly to the method and apparatus for back biasing the valve spring. 
     2. Background of the Invention 
     In internal combustion engines, air is taken into, and forced out of the combustion chambers through carefully timed operation of valves opened and closed in a combustion cycle or Otto cycle, in most designs by cam lobes mounted on, or integral with, camshafts. The valves seat within the air intake or exhaust ports, and are opened on the engagement of a cam lobe with the valve assembly, by engaging a cam follower which is connected with a valve spring through a valve spring retainer. The cam lobe engages the cam follower either directly, as through a shim, or indirectly, which is usually through a rocker arm assembly. The valve spring biases the valve into the closed position, in which position the valve head is seated within the port. Because of the great number of repetitive valve operations during the cycles of the camshaft during operation, the valve head wears on the valve seat structure and itself, so that the valve head will, with time, sit deeper within the valve seat in the cylinder head. 
     When the valve seating structure deteriorates, it is likely that the. valve will seat too far within the seating structure, reducing the clearance between the cam and the cam follower. Correction of the clearance can be accomplished by replacing the cam follower shim or other clearance adjusting instrument. Moreover, the clearance between the cam and the cam follower is sometimes important in fine tuning an engine for special performance. 
     The pressure on the cam follower-to-cam lobe interface passes through the shim or similar device. When it is desired to adjust the cam-to-cam follower clearance, either for maintenance or for performance reasons, the adjustment therefore is normally made by replacing the shim or similar device. To make such a replacement, it is necessary to obtain relief from the valve spring pressure. 
     Furthermore, the shim is very small, and normally is placed in a very inaccessible location. The shim, for example, is on the order of 0.150 inches thick. The pressure on the shim is on the order of, e.g. 160 to 220 pounds per square inch (“psi”) the pressures are on the order of as much as 600 psi. 
     Various methods and tools have been designed to assist the automobile mechanic in relieving the valve spring pressure. For example, Kammeraad, U.S. Pat. No. 3,979,811 teaches an overhead camshaft and valve tool that can be attached to the cylinder head, the ultimate objective of which is to relieve the pressure of the cams on the cam followers. The tool must be attached first to the cylinder head below the cam shaft, with shoes that each has a flange that must be positioned laterally of the cam followers. The flanges must be inserted between the cam shaft and the cam followers so that the flange in each case will be engaged by a corresponding cam lobe to depress the corresponding cam follower and valve spring. A bolt for each cam follower is positioned in a space adjacent to the cam follower but not in-line or over the cam follower, and is selectively connected to the flange through the shoe, which is rotated about a fulcrum in the form of a rod. When the cam lobe for each cam engages its corresponding cam follower through the flange, the bolt is then screw-turned into a position to maintain its corresponding cam follower in the depressed position against the valve spring&#39;s bias. Each cam follower is made to be depressed in like manner. The camshaft, with all of the valve springs&#39; pressure thus relieved, can then be removed. 
     Other tools for relieving the pressure on the cam follower from the valve springs, are shown and described in, for examples, Mote, et al., U.S. Pat. No. 3,977,064, Johnson, U.S. Pat. No. 4,446,608 and Zdral, U.S. Pat. No. 5,499,434. Mote. et al. teaches a series of steps for the removal and replacement of a valve spring assembly in a push rod and rocker arm motor. The push rod must be removed and the rocker arm must be disengaged, after which a plate is inserted over a pair of valve springs, and a threaded shaft is used to move the plate and consequently the pair of springs against their bias. 
     In each of the Johnson and the Zdral teachings, an elongated lever is rotated about a line of rotation to depress the valve spring. In Johnson, the lever is hooked onto a pivot shaft and a leg attached to the other end of the lever engages the retainer for the spring which is depressed. In Zdral, the lever is hooked around the camshaft itself, making the camshaft itself act as the pivot line. Another location on the lever engages a depressor member which depresses a retainer connected to the valve spring. Upon rotating the lever about the pivot line, the depressor member depresses the spring&#39;s retainer. In both of these devices, as well as in the device of Kammeraad, identified above, the lever must be locked in the spring-depressed mode to prevent the spring from applying pressure back against the cam or cam lobe. It has been known for the locking mechanism to surprise the mechanic and become unlocked. The result can be injury as well as sore knuckles. 
     In many engine designs, furthermore, there is no space or room for an elongated lever to be inserted into the cavity around the shim&#39;s location. 
     It is still desired, therefore, to provide a valve spring pressure relief apparatus that can be mounted so as to contact the valve spring cam follower directly, without the necessity of removing any part in the linkage between the cam lobe and the cam follower before the replacement of any part. It is desired, further, to provide a valve spring pressure relief apparatus that has a direct, or straight line of pressure without the necessity of having pressure transferring apparatus that is articulated around the camshaft. It is desired, furthermore, to provide a valve spring pressure relief apparatus that does not rely upon the working of a lever about a fulcrum or pivot line. Yet further, it is desired to provide a valve spring pressure relief apparatus which, when depressing the valve spring, does not require a locking mechanism to remain and be maintained in the spring-depressed state. 
     SUMMARY 
     In brief, in accordance with one aspect of the present invention, a valve clearance adjusting tool has a body which is mountable onto a cam bearing cap of an overhead cam internal combustion motor. A threaded screw is selectively moveable in a linear direction through the body of the valve clearance adjusting tool, to linearly position a dowel pin and its foot positioned linearly to the threaded screw. The valve clearance adjusting tool is removably mounted to a cylinder head through a cam bearing cap by an already existing cam bearing cap bolt. The methods of the present invention include the engagement by the dowel pin foot directly onto a corresponding cam follower on its edge without engaging the clearance adjustment shim, by way of movement of the threaded screw to depress the valve spring against the spring&#39;s bias, thereby enlarging the space between the cam follower and the cam and allowing better ease of access to the shim positioned on the head of the cam follower. 
     Other novel features which are .believed to be characteristic of the invention, both as to organization and methods of operation, together. with further objects and advantages thereof, will be better understood from the following description in which preferred embodiments of the invention are described by way of example. 
    
    
     DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view of a section of a camshaft in a dual overhead cam motor showing mounted therein a valve clearance adjusting tool in accordance with the preferred embodiment of the present invention; 
     FIG. 2 is a cross-section elevation of the camshaft section taken along line  2 — 2  in the perspective of FIG. 1; 
     FIG. 3 is a perspective view of a valve clearance adjusting tool in accordance with the preferred embodiment of my present invention not mounted; 
     FIG. 4 generally bottom view of the preferred embodiment of my invention as seen in FIG. 3; 
     FIG. 5 is a cross-section, elevation view of the preferred embodiment of my invention, taken along line  5 — 5  of the view of FIG. 3; and, 
     FIG. 6 is a cross-section, elevation view of the preferred embodiment of my invention taken along line  6 — 6  of the view of FIG.  3 . 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring initially to FIG. 1 of the accompanying drawings, where reference numerals correspond to like numerals used in this specification, a section  10  of a dual overhead cam motor is shown having a camshaft  12  rotatably mounted within it. The camshaft  12  has a cam  14  with a lobe  15 , and a cam  16  having a lobe  17 . In the view of FIG. 1, a third cam  18  is also shown. The camshaft  12  is held onto the cylinder head  24  by, among other things, a series of cam bearing caps including cam bearing caps  20 ,  22 . The cylinder head  24  has a space or recess  25  in which the camshaft  14  operates. The cam bearing caps  20 ,  22  are secured to the cylinder head  24  by cam bearing cap retention bolts  26 ,  28 . 
     A valve clearance adjusting tool  30  in accordance with the preferred embodiment of my invention includes a body  32 , also shown in FIG.  1 . The tool body  32  has an attaching bolt hole  33  and a pair of threaded holes, each for receiving a threaded adjusting screw assembly or threaded member assembly  34 . An Allen wrench  44  for turning a screw or threaded member  36  of the screw or threaded member assembly  34  is depicted engaged with one of the threaded adjusting screw assemblies  34 . 
     In the view of FIG. 1, the cam bearing cap bolt  28  is inserted through the attaching bolt hole  33  of the valve clearance adjusting tool  30  and through the cam bearing cap  20 , and is threaded into the cylinder head  24  to secure the adjusting tool  30  and the cam bearing cap  20  to the cylinder head  24 . 
     As better seen in the cross-section, elevation view of FIG. 2, each of the threaded adjusting screw assemblies  34  is comprised of a screw portion or threaded member  36 , a hollow hex socket head  38  for receiving an Allen wrench  44 , a dowel pin  40  and a foot  42  forming the end of the dowel pin  40 . The valve clearance adjusting tool  30  is shown in FIG. 2 positioned abutting the cylinder head  24 . The body  32  of the tool  30  has received the screw or threaded member  36  of the adjusting screw assembly or threaded member assembly  34 . The screw or threaded member  36  moves axially, when turned, along the axis of centerline  39 . 
     The cam  16  with its lobe  17  rotate about the axis of centerline  46 . The cylinder head  24  has a port  50 , here shown as an exhaust port. A poppet valve  52  is made within the cylinder head  24 , the valve  52  having a valve head, a valve stem  56  and a valve guide  58 . The valve is seated within a cam follower  60 . A spring retainer  62  is fixed on the valve stem  56 , to retain the valve spring  64 . The valve spring  64  is seated fixed to the cylinder head  24  at the lower end as shown in FIG. 2, so as to bias normally the valve head  54  in the closed position. A valve clearance adjusting shim  66  is positioned on the cap of the cam follower  60  to be engaged by the lobe  17  of the cam  16  in the rotation cycles of the camshaft  12 . 
     The dowel pin  40  and its foot  42 , as depicted in the view of FIG. 2, have been advanced axially along centerline  39  by turning of the screw or threaded member  36  so that the foot  42  has traveled through the cylinder head space  25  to abut or engage the cam follower  60  at its head. The foot  42  has been advanced so as to move the cam follower  60  axially along the centerline  70  and consequently to depress the valve spring  64 . 
     The valve clearance adjusting tool  30  of the preferred embodiment of the present invention is seen more clearly in the perspective views of FIGS. 3 and 4, where the tool  30  is shown separate and apart from its position within the cylinder head  24  of FIGS. 1 and 2, above. In FIG. 3, a perspective view seen from above the tool  30 , the body  32  of the tool  30  has the attaching bolt hole  33 . As seen better in FIG. 4, which is a perspective view seen from the bottom of the tool  30 , and in FIG. 5, which is a cross-section, elevation view taken along line  5 — 5  of FIG. 3, the hole  33  extends through the tool body  32 . The tool body  32  is shaped so as to provide a generally U-shape, defining a space  70  for fitting over the cam bearing cap, the bearing cap not being shown in these FIGS. 3 and 4. 
     The pair of adjusting screw assemblies  34  are shown threaded through the tool body  32 , best seen in FIG. 6 of the drawings, having the dowel pins  40 .and the connected feet  42  extending beyond the tool body  32 . The threaded members or screws  36  have the hexagonally shaped head  38 , seen best in FIG. 3, for receiving an hexagonal Allen wrench  44 . The screws or threaded members  36  as shown in FIGS. 3,  4 ,  5  and  6  have been turned so as to recede the assemblies  34  back through the tool body  32  from the position as shown in FIGS. 1 and 2. 
     In operation, cam bearing bolt  28  is removed from the cam bearing cap  20 . The valve clearance adjusting tool  30  then is positioned over the cam bearing cap  20 , which fits within the space  70  of the tool body  32 . The cam bearing cap bolt  28  then is inserted through the attaching bolt hole  33  and through the cam bearing cap  20  to mount, removably, the valve clearance adjusting tool  30  to the cylinder head  24 . 
     An hexagonal Allen wrench  44  is inserted into the hexagonally shaped socket head  38  of the threaded member or screw  36 , and turned to advance the adjusting screw assembly or threaded member assembly  34  into the space  25  of the cylinder head  24 . By continuing the advance of the screw assembly  34 , the foot  42  attached to the dowel pin  40 , in turn attached to the screw or threaded member  36 , engages the cam follower  60  but not the adjusting shim  66 . The cam follower  60  thus depresses the valve spring  64  to create a separation space  68  between the cam  16  and the cam follower  60  and to expose the adjusting shim  66  to being handled through the spaces  25 ,  68 . The separation space  68  is on the order of 0.23 inch, and thus presents sufficient space to dislodge the adjusting shim  66 . The adjusting shim  66  is then removed, and a new adjusting shim  66  is inserted in its place. 
     The Allen wrench  44  then is turned retrogressively to recede the screw assembly  34  back upwardly, and to allow the valve spring  64  to force, through the retainer  62 , the cam follower  60  back to its normal, biased position to seat the valve head  54  closing the port  50 . The valve clearance adjusting tool  30  is then removed from the cylinder head  24  by first retrogressively turning the cam bearing bolt  28  and freeing the tool  30 . The tool  30  is removed from over the cam bearing cap  20 , and the cam bearing bolt  28  is re-inserted into the cam bearing cap  20  to secure the cam bearing cap  20  back to the cylinder head  24 . 
     In the normal operation of the internal combustion engine, the camshaft  12  rotates, in turn rotating the cams  14 ,  16 ,  18  and cam lobes  15 ,  17 . In the combustion cycle or Otto cycle, the cam lobe  17  will engage the adjusting shim  66  once each cycle to depress the cam follower  60  against the pressure bias of the valve spring  64 . The cam follower  60 , with the appurtenant cam follower head and valve  52 , thus will move reciprocally back and forth in opposing directions along the axis  70 , best seen in FIG. 2 of the drawings. The axial alignment of the threaded member assembly or adjusting screw assembly  34  is indicated by centerline  39  in FIG.  2 . The centerline  39  is substantially parallel to the axis  70  of the valve  52  and cam follower  60 . 
     It may be seen that in the complete operation of removing the adjusting shim  66 , no normal operating component of the engine is removed, except of course for the adjusting shim  66  itself. Moreover, no operating component is moved except in a course and direction of movement which that component normally moves in the Otto cycle. 
     The foregoing detailed description of my invention and of preferred embodiments thereof as to products, compositions and processes, is illustrative of specific embodiments only. It is to be understood, however, that additional embodiments may be perceived by those skilled in the art. The embodiments described herein, together with those additional embodiments, are considered to be within the scope of the present invention, which is to be limited only by the appended claims.