BACKGROUND OF THE INVENTION 
   1. Technical Field 
   This invention relates generally to a timing tool for measuring and setting the timing of fuel injectors and more particularly to such a tool for measuring and setting plunger position and travel of unit fuel injectors. 
   2. Background Art 
   Injection timing is a critical parameter for meeting emission standards on all diesel engines, including those used in locomotive and marine engines. Exact timing of the injectors is important because retarding the injection timing can reduce NO x  emissions. However, if the injection timing is retarded beyond a target value, smoke emissions can increase above acceptable limits and the fuel consumption penalty can be excessive. 
   On many diesel engines, such as the General Motors Electro-Motive Division (EMD) engines, the fuel injection pump and spray nozzle are combined in a single compact unit called a unit injector. Unit injectors meter, atomize, and spray fuel into an associated cylinder of the engine. The pumping function of the injector is accomplished by the reciprocating motion of a constant stroke injection plunger which is actuated by an injector cam on the engine camshaft through an injector rocker arm. In the EMD engine unit injectors, the position of the plunger, and thereby the timing, is adjusted by means of a ball stud and lock nut at the injector actuating end of the rocker arm. The quantity of the fuel injected into each cylinder is varied by rotating the plunger mechanically by means of an injector control rack, or by electronically controlled valves. The plunger stroke remains constant at about ¾ of an inch. 
   The standard injection timing tool used for setting the injection timing in General Motors EMD engines is used to check the height of the injector plunger as the flywheel is set at a predetermined position. The tool has a steel shaft having a knurled end by which the tool is gripped. An end of the shaft opposite the knurled end has a narrow section that is inserted into a hole in the injector body. At the top of the narrow section, there is a step that acts as a stop to control extension of the tool into the hole so that the step rests directly on the top of the injector body. Above this step there is a larger shoulder that is adapted to be seated on a retainer element of the injector, and is spaced a predetermined distance from the step, for example 2.430 inches. It is this fixed distance between the step and the shoulder that allows the tool to be used as a feeler-type gauge for timing adjustment. The stock timing tool must be held in precise vertical alignment and requires considerable experience and a good sense of “feel” to achieve accurate and repeatable injector timing settings. 
   Injector timing tools have been developed for measuring injector plunger height on engines in which injector plunger position is controlled by an adjustable push rod connected to an end of the rocker arm opposite the plunger actuator end of the rocker arm. For example, U.S. Pat. No. 4,503,619 issued Mar. 12, 1985 to Nelsen, et al. for an INJECTOR HEIGHT MEASURING TOOL ASSEMBLY describes such a tool. However, the Nelsen, et al. timing tool cannot be used on rocker arm/injector arrangements that have the plunger adjustment means at the plunger actuator end of the rocker arm. For example, an adjustable ball stud mounted in the plunger actuator end of the rocker arm and an associated lock nut are used in the aforementioned EMD series diesel engines. This arrangement requires direct tool access to the ball stud and lock nut for adjustment of injector timing, a requirement prohibited by the Nelsen et al. timing tool which covers the plunger actuator end of the rocker arm. 
   The present invention is directed to overcoming the problems set forth above. It is desirable to have a fuel injector timing tool that does not require subjective “feel” and critical alignment to measure and set injector plunger position. It is also desirable to have such a tool that allows access to plunger position adjustment components mounted in the plunger activator end of the rocker arm. 
   SUMMARY OF THE INVENTION 
   In accordance with one aspect of the present invention, a timing tool for a fuel injector includes an elongated tubular member having a central passageway extending between upper and lower open ends. The upper end of the tubular member is adapted to receive a linear displacement measuring device. The timing tool also includes a base member having a first surface that is attached to the lower end of the elongated tubular member in perpendicular relationship with the central passageway of the tubular member. The base member also includes a second surface spaced from and parallel to the first surface that is adapted to be seated in contacting relationship on a retainer element of the fuel injector. The base member also has an aperture extending between the first and second surfaces in axially aligned relationship with the central passageway of the tubular member. The base member also has an end portion spaced from the aperture and is adapted to only partially circumscribe a plunger follower disposed on the retainer element of the fuel injector. 
   Other features of the timing tool embodying the present invention include the base member being magnetically attachable to the retainer element of the fuel injector. 
   Another feature of the timing tool embodying the present invention includes the aperture in the base member having a guide bushing disposed therein. The guide bushing has an internal diameter that is sufficient to provide guiding contact with a movable stem element of the linear displacement measuring device when the device is mounted on the upper end of the elongated tubular member. 


   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     A more complete understanding of the present invention may be had by reference to the following detailed description when taken in conjunction with the accompanying drawings, wherein: 
       FIG. 1  is a vertical view of the plunger actuator end of a rocker arm and the fuel injector timing tool for measuring and setting plunger position in accordance with the present invention; 
       FIG. 2  is a top view of the plunger actuator end of the rocker arm and the fuel injector timing tool for measuring and setting plunger position in accordance with the present invention; and 
       FIG. 3  is a vertical view of the fuel injector timing tool and a calibration block used to preset a desired extension of the stem of a measuring device below a bottom surface of the base of the timing tool. 
   


   DETAILED DESCRIPTION OF THE INVENTION 
   In accordance with the present invention, a timing tool  10  for measuring and setting the position of a fuel injector plunger  12  of a fuel injector  14 , is shown in  FIGS. 1 and 2 . The plunger  12  of the fuel injector  14  is biased upwardly by a spring  16  acting on a retainer element  18  attached to an upper end of the plunger. A cup-shaped plunger follower  22  is slidably disposed on top of the retainer element  18  and is adapted to mate with a ball end  20  of an adjustable stud  24 . The adjustable stud  24  is threadably mounted in a plunger actuator end  26  of a rocker arm  28 . A roller follower  30  is rotatably mounted at an opposite, or cam follower, end  32  of the rocker arm  28  The plunger  12  of the fuel injector  14  is reciprocally moved along a generally vertical central axis  11  by the plunger actuator end  26  of the rocker arm  28  as determined by a cam  34 . The roller follower  30  follows the predetermined profile contour surface  36  of the cam  34  and thereby controls the actual timing and position of the plunger  12 . The adjustable ball stud  24  is maintained at a desired position within the plunger actuator end  26  of the rocker arm  28  by a lock nut  38 . 
   In the preferred embodiment of the present invention, the timing tool  10  includes an elongated tubular member  40  having a central passageway  42  extending between a first, or upper, open end  44  and a second, or lower, open end  46 . The upper end  44  of the tubular member is adapted to receive a linear displacement measuring device such as a dial indicator  48 , as shown, or, if desired, other measuring devices, such as a digital linear indicator. 
   The timing tool  10  has a base member  50  having an upper, or first, surface  52 . The lower end  46  of the elongated tubular member  40  is attached to the first surface  52  of the base member  50  such that the central passageway  42  of the elongated tubular member  40  perpendicular to the upper surface  52  of base member  50 . The base member  50  also includes a lower, or second, surface  54  that is spaced from and generally parallel to the first surface  52 . The lower surface  54  is adapted to be seated directly on an upper surface  56  of the retainer  18 , perpendicular to the axis  11 . The base member  50  has an through hole, or aperture,  58  that extends between the upper surface  52  and the lower surface  54  and is in axially aligned relationship with the central passageway  42  of the tubular member  40 . Importantly, the base member  50  also an open end  60  that is spaced from the aperture  58  and is adapted to only partially circumscribe the plunger follower  20  disposed on the upper surface  56  of the retainer element  18 , and abut an outer circumferential surface of the plunger follower to accurately center the timing tool  10  on the retainer  18 . 
   The measuring device  48  has a stem portion  62  that extends through the central passageway  42  of the elongated tubular member  40 , the aperture  58  in the base member  50  and further extends for a distance sufficient to contact a predetermined upper surface of the fuel injector  14 . A distal, or contact end  64  of the stem  62  is suitably adapted to contact the upper surface of the fuel injector  14 . In one embodiment, the contact end  64  of the stem  62  is knurled to reduce the effect of an oil film that may be present on the top surface of the fuel injector  14 . 
   Desirably, a guide bushing  66  is disposed in the aperture  58  in the base member  50  and has an internal diameter sufficient to provide guiding contact with the movable stem  62  of the linear displacement measuring device  48 . 
   In a preferred embodiment of the present invention, the base member  50  of the timing tool  10  is magnetically attachable to the upper surface  56  of the retainer element  18 . The base member  50  may be formed of a magnetic or magnetized metal, or have one or more magnets recessed in, or otherwise fixedly mounted on, the bottom surface  54  of the base member  50 . Thus, when the timing tool  10  is seated on the upper surface  56  of the retainer  18 , the timing tool  10  can advantageously be used hands-free, allowing both hands to be used when adjustment is required, to loosen the lock nut  38 , adjust the ball stud  24 , and subsequently retighten the lock nut  38 . By maintaining the timing tool  10  on the retainer  18  during the adjustment process, it can be easily observed that the critically set distance adjustment is not altered during tightening of the lock nut  38 . 
     FIG. 3  shows the timing tool  10 , embodying the present invention, seated on a calibration block  68 . The calibration block  68  has an upper surface  70  that is a closely toleranced predetermined distance from a top surface  72  of a base  74 . Before using the timing tool  10  to measure and set plunger position, and accordingly the timing, of the fuel injector  14 , the timing tool  10  is positioned on the base  74  as shown in  FIG. 3 . If desired, the upper surface  70  may have a cylindrical boss (not shown) extending upwardly from the upper surface with a diameter substantially the same as the diameter of the plunger follower  10 . The cylindrical boss is thus suitably adapted to be received within, and partially circumscribed by, the open end  60  of the base member  50  and thereby center the timing tool  10  on the calibration block  68 . The movable stem  62  of the linear distance measuring device  48  is then extended until the distal, or contact, end  64  of the stem  62  is in contact with the top surface  72  of the base  74 . The indicator  48  is then “zeroed,” or if desired, offset by a predetermined value. Also, if desired, separate calibration blocks may be used to provide different timing settings. For example, specific calibration blocks can be constructed to provide calibration of the measuring device  48  equivalent to the desired position of the retainer element  18  at various predetermined crankshaft settings, such as TDC or 0°, −2°, −4°, or −6° BTDC. After the thus calibrated measuring device  48  is removed from the calibration block  68  and seated on the upper surface  56  of the retainer  18  of the fuel injector  14 , any deviation from the preset distance can be easily measured. For example, if the position of the plunger  12  is too high, the measuring device  48  will indicate a greater distance than desired between the top  56  of the retainer  18  and the predetermined surface of the fuel injector  14 . To adjust the distance, the lock nut  38  is loosened with a suitable wrench, and an adjusting tool such as a screwdriver is inserted into a slot  76  provided on a projecting end  78  of the ball stud  24 . The ball stud  24  is then adjusted downwardly until the desired predetermined distance, as indicated by the measuring device  48 , is achieved. The lock nut  38  may then be retightened to retain the ball stud  24  at the adjusted position. In a similar manner, if the dial indicator indicates that the distance between the top surface  56  of the retainer  18  and the predetermined surface of the fuel injector  14  is too short, the lock nut  38  is loosened, the adjustable ball stud  34  screwed in a reverse direction to achieve the required predetermined distance, and the lock nut  38  retightened. 
   An important benefit of the timing tool embodying the present invention includes being able to rotate the linear distance measuring device  48  so that it is readily observable during timing adjustments. Also, the timing tool  10  can be used to measure injector plunger position as a function of crank angle degrees. Such measurements are typically done to verify that the lobe on the injector cam shaft is phased correctly with the crankshaft. Heretofore this measurement has been carried out by using a dial indicator on the top of the injector rocker arm. However, the geometry of the rocker arm follows an arc, thereby contributing some error to the accuracy of the measurement. The timing tool  10 , embodying the present invention, measures only true vertical motion, thereby increasing the accuracy and repeatability of the measurements. 
   An important advantage of the injector timing tool  10 , embodying the present invention, is that it may be used with a specific software program capable of accepting readings from a digital displacement measuring device  48  as an input value and perform specific calculations. Such a process may be easily automated by using an electronic digital indicator in connection with the timing tool  10  and a shaft encoder on the engine. The digital indicator output signal and the shaft encoder output signal may both be connected to a PC, the sensed values provided directly to the software, and a plot or table made of the entire plunger travel profile. To further automate this process, the engine may be turned by a hydraulically actuated bar tool. Alternatively, the PC could be replaced with a PDA or other small microprocessor based unit that accepts the measurement signals, stores the data, performs the calculations, and displays the results. The displayed results are very beneficial in checking a unit that has been timed in the traditional manner or if one is unsure about the timing at which the engine is set. It should be noted that cam shafts are sometimes replaced to provide specific timing events. Heretofore there has been no way to easily and quickly measure injector timing variations attributable to different cam shafts. 
   Although the present invention is described in terms of a preferred illustrative embodiment, those skilled in the art will recognize that the dial indicator described herein is for the purpose of illustration, and that other measurement devices, such as digital indicators, may be used in conjunction with the injector timing tool embodying the present invention. Such measurement devices are intended to fall within the scope of the following claims. Other aspects, features, and advantages of the present invention may be obtained from a study of this disclosure and the drawing, along with the appended claims.
A fuel injector timing tool has an elongated tubular member on which a measurement device may be mounted. A lower end of the tubular member is attached to a base member disposed perpendicularly to the tubular member and has an open end that only partially circumscribes a plunger follower slidably disposed on a retainer element of the fuel injector. The timing tool permits ready access to an adjustable ball stud and associated lock nut mounted in a plunger actuator end of an injector rocker arm so that accurate plunger position can be set while the timing tool remains in place on the retainer element of the fuel injector.