US3258838A

US3258838A - Method and apparatus for finding centers

Info

Publication number: US3258838A
Application number: US392462A
Authority: US
Inventors: Jr Mclane Tilton
Original assignee: EQUIPMENT DEV CORP
Current assignee: EQUIPMENT DEV CORP
Priority date: 1964-08-27
Filing date: 1964-08-27
Publication date: 1966-07-05
Anticipated expiration: 1983-07-05

Description

July 5, 1966 Filed Aug- 27, 1964 M LANE TILTON, JR I 3,258,838

METHOD AND APPARATUS FOR FINDING CENTERS I 2 Sheets-Sheet 1 T I INVENTOR T1 II. 5. MUZAWE 7/470 4/2.

ATTORNEY S July 5, 1966 Filed Aug- 27, 1964 METHOD AND APPARATUS FOR FINDING CENTERS 2 Sheets-Sheet 2 INVENTOR We [4M5 7/2 7011/ 07a ATTORNEYS United States Patent 3,258,838 METHOD AND APPARATUS FOR FINDING CENTERS McLane Tilton, .Ir., New Canaan, (301111., assignor to Equipment Development Corporation Filed Aug. 27, 1964, Ser. No. 392,462 Claims. (Cl. 29-401) This invention relates to a method and apparatus for accurately locating the axis of an aperture in a body, and is particularly applicable to valve reconditioning operations for engines.

Valves of an internal combustion engine must be reground from time to time in order to obtain maximum performance from the engine. Optimum performance can be achieved only when each valve functions in exactly the proper manner, i.e. when each valve moves smoothly without slap or bounce, and is accurately seated so that leakage cannot occur when the valve is in the closed position. In order to achieve optimum valve operation, the internal surface of the valve guide must be rebuilt if it is worn beyond permissible limits, and also the valve face must be made precisely concentric with that portion of the stem that operates in the valve guide. The valve seat, therefore, must be ground precisely about the center of the valve guide and oriented so that its axis coincides with the longitudinal axis of the guide. Furthermore, in rebuilding the wall of the valve guide, it is extremely important that the central axis thereof be maintained as close as possible to the original central axis of the guide.

The known methods and tools employed for rebuilding the valve guide tend to follow the worn path on the valve guide wall. This automatically causes dislocation of the new central axis from the old central axis, the amount of dislocation being dependent upon the amount of wear. Further, considerable difficulty has been experienced in regrinding the valve seat so that its axis coincides precisely with the longitudinal axis of the valve guide. In fact, prior to this invention, there was not known any practical and predictable technique for rebuilding the valve guide so that its new central axis substantially coincided with the original axis, or for grinding the valve seats so that the desired registry between valve face and seat will be regularly obtained.

Accordingly, it is an object of this invention to provide a practical method and tool for rebuilding a worn bore in a body so that the longitudinal axis of the rebuilt bore coincides as close as possible with the axis of the original bore.

It is another object of this invention to provide a practical method for accurately ascertaining the location of the longitudinal axis of an aperture in a body.

A further object of the invention is to provide a method for locating the axis of a bore, so that the valve seat may be ground relative to the bore axis.

A still further object is to provide a novel tool by means of which the axis of a cylindrical aperture in a body may be more precisely located than was heretofore possible.

All of the objects, features and advantages of this invention and the manner of attaining them will become more apparent and the invention itself will be best understood by reference to the following description of an embodiment of the invention taken in conjunction with the accompaying drawing, in which:

FIG. 1 illustrates an exhaust valve, a valve guide in cross-section, and associated parts of an internal combustion engine,

FIG. 2 is an enlarged view in cross-section of the valve guide shown in FIG. 1,

' FIG. 3a illustrates one step in reconditioning the in- Patented July 5, 1966 ternal surface of the valve guide, using a novel tool in accordance with the invention,

FIG. 3b shows an enlarged view of a portion of the tool of FIG. 3a, illustrating the position of a cutting wheel in the tool,

FIG. 3c shows an enlarged view of the cutting wheel of FIGS. 3a and 3b, further illustrating its construction,

FIG. 4 illustrates a further step in reconditioning the internal surface of the valve guide,

FIG. 5 shows the valve guide as it appears after the reconditioning operation,

FIG. 6 illustrates one form of a two-piece tool employed to accurately locate the central axis of the guide valve in accordance with the invention,

FIG. 7 shows the tool of FIG. 6 in cross-section, the parts thereof being in cooperative contact relation with one another, and

FIG. 8 shows the tool in the manner employed for accurately locating the central axis of the valve guide.

Referring now to FIG. 1, there is shown a portion of an engine block 10, in which there is located an exhaust valve 12, which is adapted to move in a reciprocating manner in a cylindrical valve guide 14. The valve 12 is reciprocated by means of a cam 16 acting against the force of a spring 18 to open and close the valve. When the engine is new, the valve should open and close without occurrence of substantial friction between the valve stem 12a and the inner wall of the valve guide 14. If, however, the clearance between the valve stem 12a and the valve guide 14 is excessive or if through use, the head 12b of the valve becomes warped or distorted, the face 29 of the valve will not contact the valve seat 21 properly. Additionally, such malfunction can result from warping of the valve seat 21 due to strains resulting from uneven head bolt tension between adjacent head bolts and can also result from strain relief during operation of the engine as .a result of repeated heating and cooling of the engine block 10. Whatever the cause, when the valve does not seat properly, the valve will not move in a floating manner, but instead may slap or bounce, causing some sidewise movement. Such sidewise movement or rocker anm action can also result from, or be aggravated by, the side-directed force component of the cam 16 which actua-tes the valve 12. This is particularly true when there is excessive clearance between the valve stem 12a and the valve guide 14. The result of this rocker arm movement will appear on the internal surface of the valve guide as Worn portions, indicated at 14a and 14b in FIG. 2. These regions are generally out-of-round or somewhat egg shaped when viewed from either end of the valve guide.

When the internal surface of the valve guide is worn, as seen in FIG. 2, this surface must be reconstructed or reconditioned to rebuild the surface of the regions 14a and 14b, and also to bring the diameter of the internal surface generally to a size Where the valve stem can operate in close clearance relation therewith.

This may be accomplished by decreasing the internal diameter of the valve guide 14 by means of a novel knurling tool 20, seen in FIG. 3a. This knurling tool 20 comprises :an arbor having a lower portion 21 and an upper portion 22. The lower portion 21 is of a larger diameter than the upper portion 22 and is only very slightly smaller than the internal diameter of the valve guide bore, for a purpose which will be explained later. In the region intermediate the arbor upper and

lower portions

22 and 21 there is provided a cutout 23, see also FIG. 3b, :for receiving :a metal forming Wheel 24. This wheel 24 is positioned for rotation in the cutout 23 and is held therein by a circular spring 25 and portions 26 on the arbor lower portion 21 which are spaced apart a distance smaller than the diameter of the forming wheel axle 24a. The

- J wheel 24 is provided with a sharp metal forming edge 24b having a V-sh-aped cross-section.

In order to rebuild the inner wall or bore of the valve guide 14, the arbor upper portion 22 of the knurling tool 20 is first engaged in a suitable machine (not shown) for rotating the same. The tool 20 is then lowered so that the arbor lower portion 21 is received in the bore of the valve guide 14. The length of the arbor lower portion 21 is such that the metal forming wheel 24 cannot engage the bore until the arbor section 21 is well engaged int-o the central region 14 of the bore which is relatively unworn. Since the diameter of the arbor lower portion 21 is only slightly smaller than the unworn internal surface 140 of the bore, it will be seen that when the metal forming wheel does engage the bore it will commence the bore rebuilding process when rotating about the original longitudinal axis of the bore, and will not be affected by the extreme wear at the ends of the bore as is the case with known tools and processes.

As the tool 20 is rotated it is referenced against one side of the bore wall to cause the sharp edge 24b of the wheel 24 to operate on the opposite side of the guide wall to cold-form depressions 28. The material of the valve guide 14 is sufficiently ductile so that some of the material between the depressions 28 is displaced outwardly to form ridges 30; these ridges produce a smaller internal diameter than the unworked internal cylindrical portion seen at 140. As can be seen from FIG. So, this ridge forming operation rebuilds the badly worn sections 14a and 14b of the bore.

In order to obtain best results from the method described herein, it is important that certain criteria be met. One item of importance is that the rotational speed of the knurling tool 20 be properly selected. The speed depends upon a number of factors. One factor is the material of Which the valve guide is made, cast iron being commonly employed. The optimum speed of the tool 20, of course, also depends upon the diameter of the forming edge 24b of the wheel 24 relative to the diameter of the valve guide bore. It also depends somewhat upon the depth of penetration of the forming wheel 24 into the bore wall. -I have found that very satisfactory results are obtained by rotating the knurling tool 20 at a speed of 50- 150r.p.m.whenusing a forming wheel 24 of approximately diameter on a cast iron valve guide having :a bore diameter of approximately Too slow a speed will not produce ridges of suflicient height, resulting in insuflicient wall build-up. Too fast a speed produces local fracturing of the mate-rial in the ridge formations. I have also found that the lead angle, see FIG. 3b, is critical, best results being produced when this angle is between 1 and degrees.

The ridge forming wheel 24 of FIGS. 3a and 3b is shown in enlarged view in FIG. 3a. In a preferred embodiment the angle A may be approximately 75 where the diameter B is approximately and the diameter C is .060". Substantial viarations from these values may be made while still obtaining good results.

After the knurling tool 20 has traveled the full length of the valve guide bore and has been removed, a reaming tool 32 is employed, as seen in FIG. 4, to true up the internal surface of the valve guide 14. A second wheel slightly larger in diameter than the Wheel 24 described above is then inserted in the cutout 23 in the arbor in place of the first Wheel 24 by forcing it against the spring 25. The tool 20 is then employed in like manner as that already described to reduce further the internal diameter of the valve guide bore and to rebuild the worn areas 14a and 14b. After this second knurling operation a reaming tool of the same or smaller diameter is employed to ream the internal surface of the valve guide 14 to precisely the proper diameter for the particular valve stem to be used therewith.

The rebuilt internal structure of the valve guide provides several advantages. One advantage is that the depressions serve as oil retaining grooves. Another advantage is that the cold working of the metal imparts a greater hardness to the finished wall of the bore, so that it is more wear resistant than the original wall.

After the valve guide 14 has been reconditioned as described above and as seen in FIG. 5, the valve seat may then be ground, and as explained above, it is of great importance that the valve seat when ground be properly oriented with respect to the axis of the guide.

This is accomplished by means of a center locating tool as seen in FIGS. 6 to 8. This tool comprises a sleeve 36 and a tapered arbor 38. The sleeve 36 is provided with a longitudinal slot 40 extending the full length of the sleeve and a collar 42 at the top of the sleeve. The slot may also be a spiral or other suitable shape. The collar 42 acts as a stop when the sleeve is inserted into the reconditioned bore. The outer surface 44 of the sleeve 36 is of cylindrical shape and its inner surface is provided with a gradual taper. This taper is provided to match the tapered portion 46 of the arbor 38 as will be seen in FIG. 7.

The diameter of the outside portion of the sleeve 36 is slightly smaller than the valve guide 14 with which it is used so that it may be freely inserted into the guide, as seen in FIG. 8. After the sleeve is inserted, the tapered portion 46 of the arbor 38 is inserted into the sleeve 36', causing the sleeve to expand. This results in the outside surface 44 of the sleeve 36 engaging the internal wall or bore of the valve guide 14 along its entire length, so that the ntire center locating tool is rigidly held in the bore. Th top section 39 of the tapered arbor 38 is used to centrally position valve grinding apparatus, not shown. When the valve grinding apparatus is properly positioned and the valve seat 21 is ground, the valve seat will, in accordance with the invention, be accurately positioned with respect to both the longitudinal axis of the rebuilt bore and the original longitudinal axis thereof.

In order that the finished valve seat 21 will b concentric with the internal cylindrical surface of the valve guide 14, and also so that its plane will be perpendicular to the longitudinal axis of the valve guide, certain precautions are necessary to insure the high precision which is required. One of these precautions is that the outer surface of the sleeve 36 must be truly cylindrical so that when the sleeve is firmly engaged in the valve guide bore it cannot wobble in any direction. Another requirement is that the taper of the internal surface of the sleeve 36 and that of the tapered portion 46 of the arbor 38, be precisely identical so that the arbor does not Wobble in the sleeve. A final requirement is that the center of the arbor 38 must be located precisely on the longitudinal axis of the valve guide 14 when the tool is held in the guide.

It will be appreciated that if the bore of the valve guide is of the proper diameter and is not out-of-round, that the novel center-locating tool and method disclosed herein can be utilized without the preliminary reconditioning steps described. Furthermore, it will be apparent that although the center-locating tool is described in connection with locating the axis of a cylindrical aperture, the principles can also be applied to find the longitudinal axis of a rectangular aperture or one of still other shape. The invention is also applicable to many different uses where it is desired to locate a center or central axis with high precision.

It will be clear that the methods and tools of this invention afford substantial advantages over present practices employed in valve reconditioning and grinding operations. Thus there is now available for the first time (1) a practical method and tool for rebuilding a valve bore so that the longitudinal axis thereof coincides with the original longitudinal axis of the bore before becoming worn, and (2) a method and tool for methodically and practically locating the actual center of a bore. As a result, valves reconditioned in accordance with the teachings herein will more accurately seat and will function more smoothly since ideal floating valve action is now achieved.

This, of course, results in reduction of wear ordinarily caused by wobbling action upon opening and closing of the valve when the seat is oil-center, and also increases the period of satisfactory valve performance. Finally, engine performance and economy are improved substantially over that previously realized after valve regrinding, and such improved operation and economy continue for a much longer period of time.

While the foregoing description sets forth the principles of the invention in connection with specific apparatus, it is to be understood that the description is made only by way of example and not as a limitation of the scope of the invention as set forth in the objects thereof and in the accompanying claims.

What is claimed is:

1. A method for locating the longitudinal axis of a bore in a body which comprises the steps of engaging the bore With a knurling tool having a centerlocating portion of a diameter slightly smaller than said bore whereby said bore may be resized accurately about its original longitudinal axis,

rebuilding the bore by reducing the internal diameter thereof by continuing to advance said tool into said bore,

reaming the wall of the rebuilt bore to provide a smooth surface thereon which is concentric with said original longitudinal axis,

and accurately locating the longitudinal axis of said rebuilt bore by inserting a tool having a tight fit in said bore.

2. A method for reconditioning a worn valve assem bly which comprises the steps of engaging the bore of a valve guide with an arbor having a center-locating portion of a diameter slightly smaller than said bore whereby said bore may resized accurately about its original longitudinal axis,

rebuilding the bore by reducing the internal diameter thereof to a size slightly greater than the stem of the valve which it is adapted to receive,

inserting into said bore an expandable sleeve having a cylindrical outer wall and a tapered inner wall,

and inserting a cooperating member into said sleeve to expand the same into contact with the bore wall, whereby locating indicia on said member may be employed to position accurately valve grinding apparatus.

3. The invention described in claim 2 wherein the rebuilding of said bore includes the steps of knurling the internal surface of said valve guide by means of a cutting wheel in said arbor which rotates in the direction opposite to that of said arbor, and then reaming said bore to bring it to said reduced diameter.

4. A method for reconditioning a valve assembly which comprises the steps of engaging the bore of a valve guide with a knurling tool having a center-locating portion of a diameter slightly smaller than said bore whereby said bore may be resized accurately about its original longitudinal axis,

forming ridges on the inside wall of said bore to reduce the inside diameter of said bore,

reaming said reduced diameter bore to true-up the same,

inserting into said bore an expandable sleeve having a cylindrical outer wall and a tapered inner wall, and inserting a tapered rod into contact with the wall of said bore, whereby locating indicia on said tapered rod is employed to accurately position valve grinding apparatus adjacent said bore to grind the valve seat to a precisely desired positional relationship with respect to the longitudinal axis of said bore.

5. A method for rebuilding in a body a bore that is worn asymmetrically at the ends of said bore with respect to the longitudinal axis of said bore and relatively unwom in the central region thereof which comprises the steps of inserting into said bore an arbor having a diameter slightly smaller than the diameter of said central region so as to guide said arbor along the original longitudinal axis of said bore,

forming ridges on the inside wall of said bore by rotating said arbor to cause a sharp-edged wheel to displace local regions of material in said wall while said arboris guided as aforesaid and while said wheel is rotated in a direction opposite to that of said arbor, whereby said wall is rebuilt about said o-riginal longitudinal axis,

reaming said bore to a given diameter,

inserting into said bore a sleeve having a cylindrical outer wall and a tapered inner wall,

and inserting a cooperating member into said sleeve to urge the same into contact with the bore wall to rigidly and accurately position said member in said bore, whereby the longitudinal axis of the bore may be accurately ascertained.

References Cited by the Examiner UNITED STATES PATENTS 2,150,621 3/1939 Hall 51-241 2,567,319 9/1951 Christensen 51-241 2,795,904 6/1957 Arp 51-241 3,097,426 7/1963 Hill 29-567 3,133,344 5/1964 Keasler 29-401 3,148,564 9/1964 Ebner et al 72-126 XR 3,167,860 2/1965 Welles et a1 29-401 XR WHITMORE A. WILTZ, Primary Examiner, THOMAS H. EAGER, Examiner,

Claims

1. A METHOD FOR LOCATING THE LONGITUDINAL AXIS OF A BORE IN A BODY WHICH COMPRISES THE STEPS OF ENGAGING THE BORE WITH A KNURLING TOOL HAVING A CENTERLOCATING PORTION OF A DIAMETER SLIGHTLY SMALLER THAN SAID BORE WHERBY SAID BORE MAY BE RESIZED ACCURATELY ABOUT ITS ORIGINAL LONGITUDINAL AXIS, REBUILDING THE BORE BY REDUCING THE INTERNAL DIAMETER THEREOF BY CONTINUING TO ADVANCE SAID TOOL INTO SAID BORE, REAMING THE WALL OF THE REBUILT BORE TO PROVIDE A SMOOTH SURFACE THEREON WHICH IS CONCENTRIC WITH SAID ORIGINAL LONGITUDINAL AXIS, AND ACCURATELY LOCATING THE LONGITUDINAL AXIS OF SAID REBUILT BORE BY INSERTING A TOOL HAVING A TIGHT FIT IN SAID BORE.