1971 LT-1 replacement harmonic balancer - NCRS Discussion Boards

1971 LT-1 replacement harmonic balancer

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  • Patrick H.
    Beyond Control Poster
    • December 1, 1989
    • 11643

    1971 LT-1 replacement harmonic balancer

    Trying to help a friend with his car, and it appears that the harmonic balancer outer ring may have slipped. We hope to remove it in the next few days to verify, but it appears that the TDC mark is far away from actual TDC based on using a piston stop to find TDC and verify its position.

    Since the car is just a driver, he would rather order a replacement balancer and not worry about rebuilding what is on the car currently.

    In looking for a balancer, all of the 8 inch balancers marketed through Jegs, Summit, or other similar sellers note "except special high performance" for this size. I have a hard time believing that there is much difference between any stock replacement 8 inch balancers that would not allow any of them to work on an LT-1, but I thought I'd check here first and see if I'm missing something.

    Looking at balancers like these:

    Free Shipping - PowerBond Premium OEM Replacement Harmonic Balancers with qualifying orders of $109. Shop Harmonic Balancers at Summit Racing.




    https://www.jegs.com/i/JEGS/555/5165...791+4294828856

    Thanks for any comments.
    Vice-Chairman (West), Michigan Chapter NCRS
    71 "deer modified" coupe
    72 5-Star Bowtie / Duntov coupe. https://www.flickr.com/photos/124695...57649252735124
    2008 coupe
    Available stickers: Engine suffix code, exhaust tips & mufflers, shocks, AIR diverter valve broadcast code.
  • Ed H.
    Very Frequent User
    • November 19, 2015
    • 192

    #2
    Re: 1971 LT-1 replacement harmonic balancer

    I used these guys: https://www.damperdoctor.com/

    It was cheap and quick. I know you are looking for a replacement, but...

    Comment

    • Joe L.
      Beyond Control Poster
      • February 1, 1988
      • 43219

      #3
      Re: 1971 LT-1 replacement harmonic balancer

      Originally posted by Patrick Hulst (16386)
      Trying to help a friend with his car, and it appears that the harmonic balancer outer ring may have slipped. We hope to remove it in the next few days to verify, but it appears that the TDC mark is far away from actual TDC based on using a piston stop to find TDC and verify its position.

      Since the car is just a driver, he would rather order a replacement balancer and not worry about rebuilding what is on the car currently.

      In looking for a balancer, all of the 8 inch balancers marketed through Jegs, Summit, or other similar sellers note "except special high performance" for this size. I have a hard time believing that there is much difference between any stock replacement 8 inch balancers that would not allow any of them to work on an LT-1, but I thought I'd check here first and see if I'm missing something.

      Looking at balancers like these:

      Free Shipping - PowerBond Premium OEM Replacement Harmonic Balancers with qualifying orders of $109. Shop Harmonic Balancers at Summit Racing.




      https://www.jegs.com/i/JEGS/555/5165...791+4294828856

      Thanks for any comments.
      Patrick------


      These balancers are all the size and configuration of the 8" balancers used for 1969-70 Corvettes with 300 HP (i.e. GM #3947704 and 6272222). They have a thinner balancer ring (1-5/16") than those used for L-46 and LT-1 (1-11/16"). Actually, I think they would work OK for an LT-1 but I'd be reluctant to use one myself. Using one of these balancers would not affect pulley alignment, though, as most, if not all, small block harmonic balancers have the same dimension from end of snout to pulley mounting surface.

      The last GM version of the LT-1 balancer I can find, GM #12555879, is discontinued. I do not know if there are any aftermarket equivalents. The original LT-1 balancer was GM #3947712. This was replaced by GM #6272224 and, later, GM #12555879. The 12555879 differed from the earlier in having degree marks embossed about the perimeter.

      Incidentally, the reason why the 1-5/16" X 8" balancer, including the GM #6272222 is still available, is that this balancer was used for many 350 cid truck applications. Thus, its popularity as a replacement is great.
      In Appreciation of John Hinckley

      Comment

      • Patrick H.
        Beyond Control Poster
        • December 1, 1989
        • 11643

        #4
        Re: 1971 LT-1 replacement harmonic balancer

        Thanks Joe. I've noticed that a lot of them list as applicable to trucks, so that makes sense.

        Paragon wants over $300 for a balancer, which is ridiculous.
        We might end up getting his rebuilt, since replacements seem difficult to find.
        Vice-Chairman (West), Michigan Chapter NCRS
        71 "deer modified" coupe
        72 5-Star Bowtie / Duntov coupe. https://www.flickr.com/photos/124695...57649252735124
        2008 coupe
        Available stickers: Engine suffix code, exhaust tips & mufflers, shocks, AIR diverter valve broadcast code.

        Comment

        • Mark G.
          Very Frequent User
          • January 31, 2007
          • 177

          #5
          Re: 1971 LT-1 replacement harmonic balancer

          My personal feeling on those Summit/Jegs balancers. made in China would need to verify their accuracy, and not SFI rated. The stock ones weren't SFI rated either, but I would trust it over a made in China balancer. I'd get the original rebuilt and if originality is not a concern, I'd use a ATI balancer.

          Comment

          • John S.
            Very Frequent User
            • June 15, 2015
            • 505

            #6
            1973 L82 M21 4 Speed, very original and well documented driver/survivor
            NW Chapter Member, 2016 Bend Regional Top Flight
            73/74 TIM&JG 3rd Edition Revision Team Member

            Comment

            • Richard G.
              Extremely Frequent Poster
              • July 31, 1984
              • 1715

              #7
              Re: 1971 LT-1 replacement harmonic balancer

              You don't have to remove it to verify ring creep.

              Disconnect the battery.
              Use a stop in-place of the #1 plug. (You can buy one but I make them with an old plug)
              Rotate the motor by hand till the piston touches the plug.
              Do the same thing in the other direction.
              Split the difference between the two marks.
              The new mark is TDC on the balancer.
              Even with everything correct the TDC mark can be off because of factory tolerances.
              If you are blue printing a motor this is typically checked and verified.

              I see more incorrectly parts than slipped rings on balancers.
              Remember GM moved the TDC mark in relation to the key-way and incorrect balancers occasionally do get installed.

              Comment

              • Patrick H.
                Beyond Control Poster
                • December 1, 1989
                • 11643

                #8
                Re: 1971 LT-1 replacement harmonic balancer

                Richard,

                See my first paragraph. We already did this - twice. It’s WAY off.
                The outer ring seems to have also moved inward, which would fit the “loose ring” scenario.

                I spoke with the owner yesterday and at this point the balancer is likely going to be rebuilt.

                Patrick
                Vice-Chairman (West), Michigan Chapter NCRS
                71 "deer modified" coupe
                72 5-Star Bowtie / Duntov coupe. https://www.flickr.com/photos/124695...57649252735124
                2008 coupe
                Available stickers: Engine suffix code, exhaust tips & mufflers, shocks, AIR diverter valve broadcast code.

                Comment

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