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Thread: 1937 Knuckle motor: Currently 74", is 61" original better?

  1. #1

    Default 1937 Knuckle motor: Currently 74", is 61" original better?

    Dilemma; i just bought a 1937 Knuckle motor and it was rebuilt to a 74", but i got the old heads with it (bare). Is it better and worth more if i put it back to original? Or leave it? What would be the right thing to do before building the bike?

  2. #2
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    The early Knuck cases have been proved to be weak when bumped to 74". What flywheels are in your engine?
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  3. #3
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    If it still has the 61" flywheels in it and 74" cylinders it is a 68".
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  4. #4

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    I don't know i haven't opened it up...Is there a way to know without taking it apart?

  5. #5

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    It says 37ELXXXX on the bottom left case and matching belly numbers (original). I also got the frame, tanks speedo, engine rebuilt,tranny and floor boards (all original parts).

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    74 flywheels will not fit into '37 cases unless they are turned down in diameter or the cases were machined out. Neither option is good, the machined case being the worse of the two. Are you sure it is a 74 or does it just have later large port heads on it? If one head is off you can determine engine size easily by measuring bore and total stroke. Does it have 4 fin or 5 fin cylinders?
    Robbie Knight Amca #2736

  7. #7

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    5 fins, thanks for the help.

  8. #8
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    Quote Originally Posted by elvisp1956 View Post
    5 fins, thanks for the help.
    With or without the Fire Ring?
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