KNOCKING NOISE THREAD INTERFERENCE OF SCREWS

1982 VEHICLES EQUIPPED WITH THE HT4100 ENGINE MAY EXHIBIT A KNOCKING NOISE CAUSED BY IMPROPER CLAMPING OF THE FLEXPLATE TO THE CRANKSHAFT. THREE (3) #45 TORX BUTTON HEAD SCREWS, TORQUED TO 50 N.M (35 FT. LBS.), ARE USED TO HOLD THE FLEXPLATE TO THE CRANKSHAFT, BUT MAY NOT BE CLAMPING THE PLATE SECURELY DUE TO THREAD INTERFERENCE OF THE SCREW TO THE THREADED CRANKSHAFT HOLE. TO CHECK FOR THIS CONDITION: 1.REMOVE THE FLEXPLATE. 2.INSTALL THE THREE TORX HEAD SCREWS FINGER-TIGHT INTO THE CRANKSHAFT. 3.MEASURE THE DISTANCE BETWEEN THE CRANKSHAFT FACE AND THE UNDERSIDE OF THE SCREW HEAD (SEE FIGURE 1). THIS DISTANCE MUST BE LESS THAN 2MM (.080") ON ALL SCREWS. 4.IF THE MEASURED DISTANCE IS LESS THAN 2MM AT ALL THREE SCREWS, REINSTALL THE FLEXPLATE AND TORQUE THE SCREWS TO 50 N.M. 5.IF THE DISTANCE IS GREATER THAN 2MM AT ANY SCREW, THE CRANKSHAFT SCREW THREADS ARE IMPROPERLY MACHINED SUCH THAT THE SHOULDER OF THE FLEXPLATE SCREW BOTTOMS OUT AGAINST THE THREADS IN THE CRANKSHAFT. 6.TO CORRECT THIS CONDITION, IT WILL BE NECESSARY TO CHAMFER EACH IMPROPERLY MACHINED CRANKSHAFT HOLE USING A 9/16" DIA. DRILL. DRILL ONLY UNTIL THE CHAMFER SHOWN IN FIGURE 2 AS THE "MODIFIED HOLE" IS OBTAINED. THIS SHOULD ELIMINATE THE FIRST FULL THREAD IN THE HOLE. DO NOT CONTINUE DRILLING TO PRODUCE A COUNTERBORE. 7.CHASE THE THREADS WITH AN M10 TAP AND CLEAN OUT THE HOLE WITH COMPRESSED AIR. 8.REPEAT STEPS 2 AND 3 TO ASSURE THAT THE MODIFICATION HAS BEEN EFFECTIVE.

General Motors bulletins are intended for use by professional technicians, not a "do-it-yourselfer". They are written to inform those technicians of conditions that may occur on some vehicles, or to provide information that could assist in the proper service of a vehicle. Properly trained technicians have the equipment, tools, safety instructions and know-how to do a job properly and safely. If a condition is described, do not assume that the bulletin applies to your vehicle, or that your vehicle will have that condition. See a General Motors dealer servicing your brand of General Motors vehicle for information on whether your vehicle may benefit from the information.