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366861N Flywheel

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  • Mark H.
    Very Frequent User
    • July 31, 1998
    • 384

    366861N Flywheel

    Anyone know what this flywheel is from? Google tells me anything from boats to trucks to Corvettes. I have my doubts. In addition to the casting number, there is "GM3" and "B294/" cast on the back side. Just took it off my '64. Thanks!
  • Tom P.
    Extremely Frequent Poster
    • April 1, 1980
    • 1814

    #2
    Re: 366861N Flywheel

    Ummmmmmmmmmmmmmmmmmmmmmmm, maybe a picture would help?

    Comment

    • Mark H.
      Very Frequent User
      • July 31, 1998
      • 384

      #3
      Re: 366861N Flywheel

      Originally posted by Tom Parsons (3491)
      Ummmmmmmmmmmmmmmmmmmmmmmm, maybe a picture would help?

      Sure. Here are a couple.
      Attached Files

      Comment

      • Tom P.
        Extremely Frequent Poster
        • April 1, 1980
        • 1814

        #4
        Re: 366861N Flywheel

        Originally posted by Mark Hedberg (30810)
        Anyone know what this flywheel is from? Google tells me anything from boats to trucks to Corvettes. I have my doubts. In addition to the casting number, there is "GM3" and "B294/" cast on the back side. Just took it off my '64. Thanks!
        That looks like a VERY tyical Chevy flywheel-----------could have been used for many applications.
        The GM3 identifies the mold/die that was used when the flywheel was made (In case there was a problem, the mold could be inspected for any irregularities).
        The B294 translates to Feb 29, 1964.
        So, it seems to fit for a flywheel for a 1964 model Chevy engine-----------thus, probably the original flywheel for your car.

        Comment

        • Duke W.
          Beyond Control Poster
          • January 1, 1993
          • 15667

          #5
          Re: 366861N Flywheel

          That's a replacement that was released in the early/mid seventies, so the casting date is probably 1974, but could be '84 or possibly even '94. As is the case with finished camshafts and the assembly of camshaft and indexing pin, 366860 is the replacement part number called out in my '80 P&A catalog, and is likely the assembly of finished 366861 flywheel and ring gear.

          Early/mid seventies was the time frame when GM was running out of seven digit part numbers so they went back into the system and found old unused six digit numbers (most of which start with "3", but I've seen a few that start with "4") that tied them over until the eight digit system came online. There were no six digit part numbers released prior to about 1973 unless you go back to the forties before the seven digit system went into effect.

          A lot of Cosworth Vega unique parts are six digits because they were released in the '73 to '74 time frame.

          All Chevrolet parts that were released from the late fifties to the mid sixties begin with 37 or 38, and 39 began showing up on newly released parts in the late sixties.

          I believe the "N" stands for for nodular iron, but I don't think nodular iron was used until the L-88 flywheel, so if my understanding of the "N" is correct, what you have is a considerable upgrade from OE flywheel, which was gray iron.

          How much does it weight? The OE 327 flywheels are 30+ pounds. The L-88 flywheel is only 18 pounds.

          Duke
          Last edited by Duke W.; August 8, 2010, 11:42 AM.

          Comment

          • Cecil L.
            Very Frequent User
            • May 31, 1980
            • 449

            #6
            Re: 366861N Flywheel

            There was no Feb 29 in 1974. There was a Feb 29 in 1964 and 84.
            I believe Chevy started working with nodular iron in 62 and, as I recall, the nodular cast cranks started showing up in 64 283's.
            Aside from the 6 digit part number issue, 64 seems a possibility. Were they still casting these in 84?
            Last edited by Cecil L.; August 8, 2010, 11:52 AM.

            Comment

            • Duke W.
              Beyond Control Poster
              • January 1, 1993
              • 15667

              #7
              Re: 366861N Flywheel

              The flywheel listed in my '77 P&A catalog (the oldest one I have) is 3973452, "CAST 3791021", so an early sixties casting number was used for a late sixties release flywheel/ring gear assembly. The OE assembly number was probably an earlier sequence number. If someone has an early to mid sixties P&A, perhaps they could tell use what it says.

              Something like a change in ring gear part number would require a new assembly number even if the finished flywheel was unchanged.

              Then sometime between 1977 and 1980 a new nodular casting was released as a replacement for 327 and probably other earlier flywheels.

              I know of a known unmolested '65 L-76 that has the 021 flywheel, and I think this casting number was common to all 327s from '63 to '68.

              If there was no Leap Year in '74, but if there was in '84 then that pretty much nails down when the subject flywheel was cast. It could not have been cast in 1964. There were no six digit part numbers released in the sixties nothwithstanding the fact that the part number does not show up until after 1977.

              Duke
              Last edited by Duke W.; August 8, 2010, 12:46 PM.

              Comment

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

                #8
                Re: 366861N Flywheel

                All------


                The original flywheel used for all 1963-68 Corvettes with small block was GM PART #3791022 and CASTING #3791021.

                The GM #3791022 was discontinued from SERVICE in December, 1971 and replaced by GM PART #3973452. I'm not sure what the casting number of this flywheel was. It may have remained 3791021 or it may have changed to 3973453 or some other number. However, I believe it did change to 3973453 or some other number close to that and I believe this was a nodular iron, "N" suffixed flywheel.

                The GM #3973452 was discontinued from SERVICE in June, 1977 and replaced by GM #366860, CASTING number 366861N. The "N" does refer to nodular iron material.

                All of the above flywheels are "standard weight" (i.e. 28-30 lb), 12-3/4", 153 tooth ring gear pieces.

                In the case of the particular flywheel in question, the year portion of the date code must refer to 1984 since the flywheel was not in production as of 1964 or 1974. It was still in production as of 1994 but there was no 2/29 in 1994. It was out-of-production and discontinued by 2004.
                In Appreciation of John Hinckley

                Comment

                • Tom P.
                  Extremely Frequent Poster
                  • April 1, 1980
                  • 1814

                  #9
                  Re: 366861N Flywheel

                  Most interesting and informational!
                  Thanks for that information regarding 6 vs 7 digit parts numbers.

                  Comment

                  • Duke W.
                    Beyond Control Poster
                    • January 1, 1993
                    • 15667

                    #10
                    Re: 366861N Flywheel

                    As I said in my previous post, my [September] 1977 P&A catalog lists 3791021 as the casting number for the 3973452 flywheel/ring gear assembly for '63 to '68 327s.

                    Likely the next release of the P&A carried the new part number, or it was added when the existing supply of old parts was exhausted. IIRC a new P&A catalog was published every three months in that era, but if the old supply was exhausted you got the new part.

                    Duke

                    Comment

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

                      #11
                      Re: 366861N Flywheel

                      Originally posted by Duke Williams (22045)
                      The flywheel listed in my '77 P&A catalog (the oldest one I have) is 3973452, "CAST 3791021", so an early sixties casting number was used for a late sixties release flywheel/ring gear assembly.

                      Duke
                      Duke-----

                      Parenthetical casting number information found in the "part description" column of P&A Catalogs can be very inaccurate. In many cases, and particularly for a part which has been superceded one or more times, it will be an anachronism. That's because the parenthetical casting number information is rarely, if ever, updated when the part number and/or casting number changes. So, the casting number information is accurate for the ORIGINAL part used for an application but not necessarily accurate for a replacement part.
                      In Appreciation of John Hinckley

                      Comment

                      • Duke W.
                        Beyond Control Poster
                        • January 1, 1993
                        • 15667

                        #12
                        Re: 366861N Flywheel

                        Originally posted by Tom Parsons (3491)
                        Most interesting and informational!
                        Thanks for that information regarding 6 vs 7 digit parts numbers.
                        Thanks to Art Armstrong who explained it here a few years ago and solved the mystery (to me) of why so many Cosworth Vega engine and fuel system parts are six rather than seven digits.

                        There are also six digit Corvette parts from that era, and I expect other GM divisions may have also used some six digit numbers in that era.

                        Duke

                        Comment

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

                          #13
                          Re: 366861N Flywheel

                          Originally posted by Duke Williams (22045)
                          Thanks to Art Armstrong who explained it here a few years ago and solved the mystery (to me) of why so many Cosworth Vega engine and fuel system parts are six rather than seven digits.

                          There are also six digit Corvette parts from that era, and I expect other GM divisions may have also used some six digit numbers in that era.

                          Duke

                          Duke-----

                          With respect to the 3XXXXX and 4XXXXX series of 6 digit part numbers, these apply to about 1973 through about 1979 released Chevrolet part numbers. After about that time Chevrolet went to 8 digit part numbers of the series 14XXXXXX and other 8 digit series.

                          I don't think the other car lines went to the 6 digit, "reclaimed" part number series because, for the most part, they did not run out of 7 digit part numbers of their assigned part number series as early as Chevrolet did. Of course, the other divisions often used Chevrolet parts for their cars, so the 6 digit Chevrolet part numbers would show up on their cars and in their P&A Catalogs.

                          Supposedly, the need for Chevrolet using the "reclaimed" 6 digit number series was because they ran out of 7 digit numbers after about 1972 and the system was not ready for the introduction of 8 digit part numbers. Curiously, though, other GM divisions started using 8 digit part numbers WAY before Chevrolet did. For instance, AC-Rochester started using 8 digit numbers in late 1973.
                          In Appreciation of John Hinckley

                          Comment

                          • Mark H.
                            Very Frequent User
                            • July 31, 1998
                            • 384

                            #14
                            Re: 366861N Flywheel

                            Thanks to all!

                            Comment

                            • Mark G.
                              Very Frequent User
                              • March 1, 2001
                              • 227

                              #15
                              Re: 366861N Flywheel

                              Mark -

                              This is a possibility.



                              Mark

                              Comment

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