Abstract:
A method and apparatus for the removal of a broken stud from a cylinder head, and rehabilitation thereof, includes a precise alignment block for attachment to at least two intact studs or stud bores of a cylinder head for alignment of a pilot port over the broken stud. Further holes in the block along the length of the block match a stud pattern of a cylinder head of pre-determined stud spacing. The apparatus comprises a series of replaceable steady pilots and corresponding rotary tools in pairs, including an end mill and cooperating milling pilot for flat or concave milling of the end of the broken stud; a drill bit and cooperating drilling pilot for drilling the end of the broken stud; and a tap and cooperating threaded tapping pilot to form new threads in the cylinder head for accepting a new replacement stud. Optionally, a threaded coil insert can be used in the newly prepared stud bore, having outer threads matching the new threads and having inner threads matching a replacement stud.

Description:
FIELD OF THE INVENTION  
       [0001]     This invention relates to automotive tools, more specifically to a method and apparatus to remove a broken cylinder head stud and to prepare a stud bore for a replacement stud.  
       BACKGROUND OF THE INVENTION  
       [0002]     Stud breakage in cylinder heads is a well-known problem and typically occurs with exposure to severe heat over time and subsequent attempts at removal. Most commonly, the threaded fastener such as a stud nearest the firewall is prone to breakage, as it is exposed to the highest degree of heat. When a stud bolt breaks off in the cylinder head, it leaves in the threaded bore a threaded portion which must be removed prior to insertion of a new stud. Due to restricted and tight access to the broken stud in the engine compartment, typically the entire cylinder head is removed from the vehicle and is repaired at a bench utilizing, among other tools, including and drill press and extractors. This process is time consuming and can requiring days for this service.  
         [0003]     Others have contemplated providing jigs or drill guides for removal of broken studs for other uses. Some having a series of pilots adapted for rotary tools, and others aligning a hole over a broken stud by bolting onto two remaining studs.  
         [0004]     For instance, in another instance of automobile maintenance, others have modified an engine timing case to include a perpendicular locking bolt to secure a dowel alignment. As suggested by a Doge Truck enthusiast at a web page www.dodgeraw.org, a jig includes an alignment block with two parallel holes to secure a guide plate to a flange attachment to the timing case. A third hole perpendicular to the first two holes accepts removable and interchangeable steady pilots. The pilot holes or guides are adapted for a variety of different rotary tools such as a drill, tap, and counter sink. The intact flange is drilled, tapped and countersunk for accepting a dowel pin locking bolt. The procedure is not to replace a broken component but to add a bolt where none existed previously.  
         [0005]     Others have applied three-hole jigs to remove broken studs including drilling a jig hole for removal of a broken axle-end studs using two other intact studs. A drill and an extractor are applied. Applicant is not aware of such devices including means for replacement of the stud.  
         [0006]     A device is needed that provides precise alignment over a broken cylinder head stud, while providing the tools to not only effectively remove the broken stud, but to adequately prepare the stud bore for insertion of a new stud.  
       SUMMARY OF THE INVENTION  
       [0007]     An alignment block attaches to a cylinder head and acts as a precise guide to efficiently remove a broken stud in a stud bore of the cylinder head while the cylinder head remains in the vehicle. The alignment block also allows for the preparation of the stud bore for insertion of a new intact stud. Herein, the term stud applies equally to the use of threaded fasteners including studs and cap screws and one, or the other, or both may be used or substituted throughout.  
         [0008]     Broadly, a tool for removal of a broken stud in a stud bore of a cylinder head, and rehabilitation thereof, comprises an alignment block adapted for attachment to at least two intact stud bores of a cylinder head. At least one pilot port is located in the block for alignment over the broken stud. A series of steady pilots for removing the broken stud and rehabilitating the stud bore, are removeably secured to the pilot port. A series of rotary tools correspond to the steady pilots and form pairs, the rotary tools for removal of the broken stud from the stud bore, and rehabilitation thereof. The series of pilot and rotary tool pairs comprise an end mill and cooperating milling pilot for flat or concave milling of the end of the broken stud; a drill bit and cooperating drilling pilot for drilling the end of the broken stud; and a tap and cooperating threaded tapping pilot to form new threads in the cylinder head.  
         [0009]     Preferably, the tap forms oversized threads for installation of a coiled insert into the stud bore. The shape of the alignment block is an elongate, running a length of the cylinder head. A full or partial block member are available and comprise at least 2 holes for securing to two intact studs or stud bores, and at least one hole acting as a pilot port and aligning over the broken stud.  
         [0010]     In one aspect, a process for removal of a broken stud in a stud bore of a cylinder head, and rehabilitation thereof, comprises the steps of removing an exhaust manifold to reveal the broken stud and the intact bores or studs; fitting an alignment block over at least two intact studs, or stud bores, and securing in place the alignment block over at least two stud bores, or stud bores, in the cylinder head and securing in place through holes in the alignment block, such that a pilot port in the block is aligned over the broken stud; installing a milling pilot to the pilot port and milling using a cooperating end mill for flat or concave milling of the end of the broken stud; installing a drilling pilot to the pilot port and drilling using a cooperating drill bit to remove the stud and threads for drilling the end of the broken stud; installing a tapping pilot to the pilot port and tapping the stud bore using a cooperating tap to form new threads in the stud bore; and fitting a replacement stud into the rehabilitated stud bore.  
         [0011]     More preferably, the process further comprises inserting a coiled insert into the stud bore, after the tapping step, the coiled insert having outer threads matching the new threads and having inner threads matching a replacement stud.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]      FIG. 1  is an example of a prior art repair of a cylinder head utilizing removal from the vehicle and extraction of broken bolt at a drill press;  
         [0013]      FIG. 2  is a perspective view of a cylinder head such as that from a Chevrolet 350 cu/in engine and jigs according to two embodiments of the invention, either a short length, rotatable jig and a singe long jig plate suitable for the entire head;  
         [0014]      FIG. 3  is a perspective view of a cylinder head, intact bolts and a broken bolt awkwardly positioned adjacent a vehicle firewall;  
         [0015]      FIG. 4  is an exploded top view showing the short length jig of  FIG. 2  aligned with the head of  FIG. 3  and further illustrating a sequence of pilots and rotary tool pairs used to remove and replace the broken stud; and  
         [0016]      FIG. 5  is a perspective view of a vehicle engine compartment requiring exhaust stud extraction using a preferred embodiment of the invention to remove the broken stud.  
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0017]     With reference to  FIG. 1 , a conventional prior art technique involves a labor intensive removal of a cylinder head  12  from the vehicle  4  for repair on the bench including use of a drill press  5  and then a re-installation of the head on the vehicle, including use of new head gaskets.  
         [0018]     With reference to  FIGS. 2-5 , embodiments of the invention are illustrated for ease of repair on the bench or the head can remain in the vehicle and increasing productivity by increasing the efficiency of the process.  
         [0019]     In either instance, an alignment block  10  removeably attaches to a cylinder head  12  and aids in providing a precise guide to efficiently remove a broken threaded fastener  30  such as the broken threaded end  14  of a stud  30  or cap screw  30   b  in a stud bore  16  of the cylinder head  12 . The invention also allows for the preparation of the stud bore  16  for insertion of a replacement fastener  54 .  
         [0020]     As shown in  FIG. 2 , alignment block members  18  are provided and which are adapted to a particular cylinder head  12  having known pre-determined spacing of studs  30  (although Chevrolet typically uses cap screws  30   b ) fit to intact stud bores  16 . A short length alignment member or block  10   a  is adapted with a minimum of three holes  20 . The holes  20  are spaced to fit a particular cylinder head  12 . A head from a particular line of Ford Motors heads will have one pattern  33  and those from a different Ford engine or those from a Chevrolet engine will have a different spacing. There are a finite number of engine and head patterns  22 . As shown in  FIG. 2 , a short block  10   a  fits a stud pattern  22  of a Chevrolet 350 cylinder head, or another cylinder head carrying the same stud pattern  22 . Similarly, a larger full length alignment block  10   b  can be implemented and which extends along the entire head  12 . Any one of the holes  20  of an alignment block  10  can act as a pilot port  24  as a broken stud  14  may appear at any one of the locations on the head. Other combinations of alignment blocks can be provided having lesser or greater numbers and arrangements of holes  20 .  
         [0021]     As shown in  FIG. 3 , one can see that after removal of the exhaust manifold and any other interferences, the broken threaded end  14  is typically the last stud nearest a firewall  26 .  
         [0022]     With reference to  FIG. 4 , a series of steady pilot and rotary tool pairs  28  (A-C) correspond with the pilot port  24 , and removeably attach to the pilot port  24  for removal of the broken threaded end  14  and preparation of the stud bore  16  for a replacement stud  54 .  
         [0023]     The alignment block  10  acts as a base plate and securely attaches to a clean surface of the cylinder head  12 . At least two holes  20  in the alignment block  10  fit over two sound or intact studs  30 , or intact stud bores  16 , while the pilot port  24  aligns over the broken stud  14 . A short alignment block  10  is shown and is illustrated with at least one threaded pilot port  24 . All three holes may be threaded (two outside holes shown for illustration) so as to alternatively acting as a pilot port  24  or as a mere bolting port  25  (middle hole shown with dotted lines for an optional threaded port  24 , or the solid line option for a mere bolting port  25 ). Accordingly, a bolting/pilot port  25 , 24  can include a bolting pilot  26  for close fit to an intact stud bore  16  and stud  30   a  or cap screw  30   b  for precise aligning of the alignment block  10 . Optionally, the alignment block  10  may have only one pilot port  24 , and at least two bolting ports  25  (illustrated with one bolting/pilot port  25 , 24  and one solely acting as a bolting port  25 ) which are sized to the existing and intact studs. Such an alignment block would be suitable only for repair at one stud location.  
         [0024]     As shown, the alignment block  10  is secured to each of the two intact studs  30 , or stud bores  16  with suitable means, such as a nut  31 , or where the intact stud has already been removed then with a cap screw  30   b  or bolt (not shown), respectively.  
         [0025]     The pilot port  24  in the block  10  accepts a series of pilot and rotary tool pairs (also shown in  FIG. 4 ). Two pairs (A,B) aid in the removal of the broken stud, while a third pair (C) prepares the stud bore for a replacement fastener  54 .  
         [0026]     The first pair of tools (A) is a milling pilot  34  and an end mill  36 . This tool pair (A) is used to remove a small amount of the broken threaded end  14 , squaring off the exposed end of the broken threaded end  14  for preparation for the next step. The second pair of tools (B) is a drilling pilot  40  and a drill bit  42 . Precise drilling can commence at the milled face. This tool pair (B) allows the broken threaded end  14  to be drilled out of the head. Preferably, a left-hand (LH) drill bit is used to aid in removal of the broken threaded end  14 . Usually the technician will note the milling and drilling depth due to a change in resistance, however, depth gauges or tools of limited length may be used to avoid over drilling.  
         [0027]     Clearly in some cases, early in the drilling step, the LH bit will break the broken stud free of the head and extract it without the need for further repair. In such cases, only a replacement fastener  54  need be re-installed. However typically, the broken threaded end  14  will not yield so easily. Accordingly, the drill bit  42  drills out the broken threaded end  14  and at least a portion of the threads of the stud bore  16 , resulting in an oversize hole.  
         [0028]     Thus, the third and final tool pair (C) is a tapping pilot  46  and a tap  48 . The tap  48  is slowly rotated down into the now empty stud bore  16 , re-threading the stud bore  16  to allow for the insertion of a threaded coiled insert  50 , such as a Heli-coil™, which fits the oversized threaded stud bore  16  and accepts a new standard size stud  30   b . It is possible to use a custom stud having an oversized root diameter for threading into the oversize hole, but is more usual to use the insert and a standard stud  30 .  
         [0029]     Each pilot  34 , 40 , 46  is secure as it threads into the pilot port  24  to ensure the correct alignment of its corresponding rotary tool  36 , 42 , 48 . The tool pairs (A), (B), and (C) ensure the drilling and tapping are precise and permit reinstallation of the intact stud and exhaust manifold after repair. The rotary tools  36 , 42 , 48  attach to a rotary drive tool (not shown), such as a drill.  
         [0030]     Referring back to  FIG. 2 , an alternative embodiment of the invention is to have a longer or even a full length alignment block  10  with enough holes  20  to provide access to all stud bores  16  in the cylinder head  12 . Similarly, this option provides at least two holes  20  for securing the block  10  to the cylinder head  12 , while all other holes  20  align over other intact or broken studs  14 . All holes  20  can act as pilot ports  24  allowing the series of pilots and rotary tool pairs (A)-(C) to access any one of the stud bores  16  in the cylinder head  12 .  
         [0031]     The process for in-the-vehicle repair is best shown in  FIG. 5 . To attach the alignment block  10  to the cylinder head  12 , an exhaust manifold is removed to reveal the cylinder head  12  containing the broken stud  14 , as well as the intact studs  30 . Once the exhaust manifold is removed the surface of the cylinder head  12  may be cleaned of residual gasket material as necessary. As previously described, the alignment block  10  is mounted to the cylinder head  12  such that the pilot port  24  is over the broken stud  14 . The other 20 holes are fit with bolting pilots  25  as necessary secured to intact studs or stud bores  30  using suitable bolts.  
         [0032]     The milling pilot  34  is first threaded into the pilot port  24 . The mill  36  is installed in a rotary drive tool (not shown). The mill  36  is stabilized by the milling pilot  34  and the rotary drive tool to protect the stud bore  16  from damage by ensuring the broken threaded end  14  is milled along its major axis. The milling pilot  34  accurately guides the mill  36  such that it is in square and axial alignment with the broken threaded end  14 . Once the accessible surface of the broken threaded end  14  is relatively flat, or concave, the mill  36  and then milling pilot  34  are removed from the pilot port  24 .  
         [0033]     The drilling pilot  40  is now threaded into the pilot port  24  to replace the milling pilot  34 . The drill bit  42  is installed in the rotary drive tool. The stud bore  16  is protected and the drill bit  42  is guided as described above for the milling process. The drill bit  42  is preferably left-handed allowing the bit  42  to aid in an early extraction of the broken threaded end  14  as discussed previously for extraction of a broken stud  14  without the need for further drilling or the conventional extraction tool.  
         [0034]     In cases where the stud bore  16  is drilled, the drill bit  42  and drilling pilot  40  can be removed from the pilot port  24 .  
         [0035]     The tapping pilot  46  is now threaded into pilot port  24 . The tap  48 , such as a Heli-coil™ STI tap, is rotated into the tapping pilot  24  and carefully rotated down into the oversize stud bore  16  using an appropriate socket and ratchet, or other similar drive tool. A forward and backward motion of the tap  48  as it is slowly rotated into the stud bore  16  creates new threads along the stud bore  16 . Once the stub bore  16  has been re-threaded, the cuttings are cleared away and the tap  48  and tapping pilot  46  are removed from the pilot port  24 .  
         [0036]     The tap  48  creates oversized threads in the stud bore  16 . In such a situation, a coiled insert  50 , such as a commercially available Heli-Coil™, is threaded down into the newly threaded stud bore  16 , the coiled insert  50  having outer threads matching the new threads and having inner threads matching a replacement fastener  54 .  
         [0037]     A suitable hand tool  51  is employed to drive the Heli-coil™ into the threaded stud bore  16 . The coiled insert  50  accommodates a standard bolt or stud. The alignment block  10  is removed from the cylinder head  12  and a new, intact stud is installed in the rehabilitated stud bore  16 . One could also remove the alignment block  10  before inserting the Heli-coil™ as this is a matter of convenience and mechanic preference.