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Technical Early 270ci GMC Cranks

Discussion in 'Traditional Hot Rods' started by Little Terry, Nov 25, 2021.

  1. Little Terry
    Joined: Oct 17, 2007
    Posts: 537

    Little Terry
    Member

    Hi there. I have an early (46-54) GMC motor and am looking into mating it up to a Winters internal clutch transmission. They are available with a range of crank couplers. These basically bolt to the rear of the crank and have a female splined section that the input shaft locates into.

    The question is, will I be able to bolt one of their early or late SB Chevy couplers to the rear of my GMC, or will I end up redrilling or making something to fit? I guess i need to consider flange diameter and bolt pattern.

    Any experience of using this type of transmission would be greatfully recieved. Apparently they are available for cloded driveline applications and can be fitted with a starter.

    It is to replace the in/out box that is currently fitted to my sprint car to make it more useable and so that i can start it independently. IMG-1250.jpg IMG-1247.jpg

    Thanks
    Mark
     
  2. 50John
    Joined: Jun 24, 2005
    Posts: 160

    50John
    ALLIANCE MEMBER

    There are two different GMC flywheel bolt patterns but to my knowledge neither match the small block. I did have a small block steel flywheel redrilled to fit a GMC so that might be a solution.
     
    Okie Pete and Little Terry like this.
  3. Bump up for the late crowd..........
     
  4. Gofannon
    Joined: Feb 8, 2007
    Posts: 722

    Gofannon
    Member

    Is your crank flange 4 bolt or 6 bolt? Early cranks were 4 bolt, later were 6. 4 bolt is the same as pre war Chevy. I have heard but cannot confirm that the 6 bolt is the same as late 50's Pontiac.
     

  5. jimmy six
    Joined: Mar 21, 2006
    Posts: 10,303

    jimmy six
    ALLIANCE MEMBER

    6 was a pattern of their own as the timing marks were on the back side and seen thru a hole in bell housing.. I fits only one way. A friend has an in-and-out coupler to bolt to the 6 bolt GMC crank flange but loves 500 miles from me.
    I can give you the diameter of a 6 bolt Crank flange if you want to see how it matches up with the Chevrolet. I believe the center purchase is the correct size. If the SBC-BBC flange is large enough redrilling it will work. I too have a BBC flywheel with 12 holes.
     
  6. Little Terry
    Joined: Oct 17, 2007
    Posts: 537

    Little Terry
    Member

    Thanks guys. I don't know whether i have 4 or 6 bolt yet. as the car is still assembled. However, it sounds like i will need to redrill the Chevy coupler or maybe even make one to fit.
    Appreciate your help on this.
     
  7. jimmy six
    Joined: Mar 21, 2006
    Posts: 10,303

    jimmy six
    ALLIANCE MEMBER

    A 4 hole crank maybe a little harder to miss the 6 on the adapter. Every 270 4 bolt crank I saw used for racing was drilled for 8 bolts. The 4 hole did have registers on the crank flange as I remember…
     
    Little Terry likes this.

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