72 LT1 timing tab - NCRS Discussion Boards

72 LT1 timing tab

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  • Fred H.
    Very Frequent User
    • December 4, 2019
    • 309

    72 LT1 timing tab

    Does anyone sell a correct 72 LT1 replacement timing tab? Presently our LT1 (8" harmonic balancer) has what apparently is a 71 LT1 timing tab and we would like to replace it for judging purposes.
    Fred Hickey
    Care taker of Top Flight 72 LT1 C60 Convertible #26756

  • David L.
    Expired
    • July 31, 1980
    • 3310

    #2
    Re: 72 LT1 timing tab

    Fred,
    IN my 40 year collection of parts I do have a NOS timing tab, GM # 3991436, for a 72 Corvette w/SHP 350.
    Dave

    Comment

    • David H.
      Extremely Frequent Poster
      • June 30, 2001
      • 1521

      #3
      Re: 72 LT1 timing tab

      Originally posted by Fred Hickey (66564)
      Does anyone sell a correct 72 LT1 replacement timing tab? Presently our LT1 (8" harmonic balancer) has what apparently is a 71 LT1 timing tab and we would like to replace it for judging purposes.
      Fred

      What is the assembly date of your engine?

      Dave
      Judging Chairman Mid-Way USA (Kansas) Chapter

      Comment

      • Fred H.
        Very Frequent User
        • December 4, 2019
        • 309

        #4
        Re: 72 LT1 timing tab

        Hi Dave, the casting date is F 10 72 the build date is 7/21/1972
        Fred Hickey
        Care taker of Top Flight 72 LT1 C60 Convertible #26756

        Comment

        • Fred H.
          Very Frequent User
          • December 4, 2019
          • 309

          #5
          Re: 72 LT1 timing tab

          To hopefully clarify my inquiryimage000000014.jpg I've attached photo that represents the correct 72 LT1 (8" harmonic balancer equipped) timing tab.
          Fred Hickey
          Care taker of Top Flight 72 LT1 C60 Convertible #26756

          Comment

          • Joe L.
            Beyond Control Poster
            • February 1, 1988
            • 43211

            #6
            Re: 72 LT1 timing tab

            Originally posted by Fred Hickey (66564)
            To hopefully clarify my inquiry[ATTACH=CONFIG]108998[/ATTACH] I've attached photo that represents the correct 72 LT1 (8" harmonic balancer equipped) timing tab.

            Fred------


            How do you know that this is a correct configuration 1972 LT-1 timing tab?
            In Appreciation of John Hinckley

            Comment

            • Leonard M.
              Very Frequent User
              • September 7, 2009
              • 236

              #7
              Re: 72 LT1 timing tab

              Joe, His picture looks identical to the original shown in the J.G., Fig, M 8.9

              Comment

              • Fred H.
                Very Frequent User
                • December 4, 2019
                • 309

                #8
                Re: 72 LT1 timing tab

                Reference 1970 -1972 7th edition TiM & JG pages 138 -139NCRS tt 2.jpgncrs tt 1.jpg
                Fred Hickey
                Care taker of Top Flight 72 LT1 C60 Convertible #26756

                Comment

                • Fred H.
                  Very Frequent User
                  • December 4, 2019
                  • 309

                  #9
                  Re: 72 LT1 timing tab

                  I recently received a alleged correct photo 72 LT1 timing tab, from (a restored)
                  survivor (with an November 71 build date). This timing tab looks the 71 tab (in the TIM / JG) ?

                  Jim 2.jpg



                  Jim Steele's.jpg
                  Last edited by Fred H.; November 5, 2021, 01:15 PM.
                  Fred Hickey
                  Care taker of Top Flight 72 LT1 C60 Convertible #26756

                  Comment

                  • Terry M.
                    Beyond Control Poster
                    • September 30, 1980
                    • 15595

                    #10
                    Re: 72 LT1 timing tab

                    Originally posted by Fred Hickey (66564)
                    I recently received a alleged correct photo 72 LT1 timing tab, from (a restored)
                    survivor (with an August or September 71 build date). This timing tab looks the 71 tab (in the TIM / JG) ?


                    [ATTACH=CONFIG]109011[/ATTACH]
                    I suggest you begin to track the engine build dates of the examples you are seeing. In the TIM&JG the word "typical" carries a lot of weight. It basically means that we haven't tracked the examples cited. Yopu would be doing yourself and many others taking on this task.
                    Terry

                    Comment

                    • Fred H.
                      Very Frequent User
                      • December 4, 2019
                      • 309

                      #11
                      Re: 72 LT1 timing tab

                      I'm attempting to determine when GM began using the the 72 tag (from the 71 timing I believed used in the early 72 production run) as referenced in the TIM / JG

                      Hopefully I will receive some additional input on any survivor 72 LT1's (and be possibly able to correlate the date GM started using what is really OEM correct.
                      Fred Hickey
                      Care taker of Top Flight 72 LT1 C60 Convertible #26756

                      Comment

                      • Joe L.
                        Beyond Control Poster
                        • February 1, 1988
                        • 43211

                        #12
                        Re: 72 LT1 timing tab

                        Originally posted by Fred Hickey (66564)
                        I recently received a alleged correct photo 72 LT1 timing tab, from (a restored)
                        survivor (with an November 71 build date). This timing tab looks the 71 tab (in the TIM / JG) ?

                        [ATTACH=CONFIG]109012[/ATTACH]



                        [ATTACH=CONFIG]109011[/ATTACH]

                        Fred------


                        This is the only configuration of the 1971-80 8" balancer timing pointer that I am aware of. The only part number ever catalogued by GM for this part is 3991436. It's possible there were 2 configurations of this part number but every known example of the 3991436 that I have ever seen is of the configuration pictured here.
                        In Appreciation of John Hinckley

                        Comment

                        • Fred H.
                          Very Frequent User
                          • December 4, 2019
                          • 309

                          #13
                          Re: 72 LT1 timing tab

                          That's the timing tab we have. I began chasing the issue when e received a deduction (mechanical page 2 #8 distributor & coil) with the note "timing tab is 71 SB like Fig M 8.9". If that is correct we'll accept it, however there appears to be both 71 & 72 tabs used in the 72 production run?
                          Fred Hickey
                          Care taker of Top Flight 72 LT1 C60 Convertible #26756

                          Comment

                          • David L.
                            Expired
                            • July 31, 1980
                            • 3310

                            #14
                            Re: 72 LT1 timing tab

                            I am sure that Chevrolet used up the 71 tabs until they were all gone and probably mixed them up with 72 tabs. Neither I or Joe has ever found GM part numbers for the 71 or 72 tabs because apparently the different part numbers do not exist. GM was in the business to make money and substitutions on the assembly were sometimes necessary.
                            As best as I can recall the assembly line ran out of 1965 grills near the end of 1965 production so they installed 1966 grills on late 1965 Corvettes.
                            Dave

                            Comment

                            • Gary B.
                              Very Frequent User
                              • July 31, 1979
                              • 926

                              #15
                              Re: 72 LT1 timing tab

                              The tab in the 70-72 TIM&JG is from 72 LT1 VIN 20571. Very original, unrestored car. J04 (May) build date.
                              Gary B

                              Comment

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