Tell me why I can't use a 4strk prop on a 2strk

Discussion in 'Prop Shop' started by TomFL, Mar 8, 2009.

  1. TomFL

    TomFL Well-Known Member

    I swapped the prop from the 4-stroke to the 2-stoke and the shaft size is the same, although the hub depth is a little shallower, something that could easily be made up with 2-3 thick washers or a spacer.

    Is there a specific reason why they are designated 2 vs 4 stroke props?

  2. Brett

    Brett > PRO STAFF <

    Pitch is pitch, and diameter is diameter. It's not the blades.
    I wonder if the exhaust openings are different.
    Could be different lower units on the 2 types.

  3. B.Lee

    B.Lee Well-Known Member

    Tell us what motors we are comparing, and I'll tell you why.  

    Most times it's as simple as needing the correct thrust washer for the prop application, sometimes they are completely different.
  4. TomFL

    TomFL Well-Known Member

    4-stroke merc 25 efi 2006
    2-stroke merc 25 1994 and 1998

    can PM serial #'s if you like

  5. Un-shore

    Un-shore Well-Known Member

    When 2 strokes are phased out there will be tons of 2 stroke props out there and they won't be able to sell any 4 stroke props.

    I dunno, are the pitches the same or do the 2 stroke turn at higher RPM so the pitch would be different from 4 stroke?
  6. Brett

    Brett > PRO STAFF <

    I wonder if you could press the spline out of the hub from one prop
    and press it back into another. That'd be something any machine shop could do.
    Yes, no, maybe?
  7. costefishnt

    costefishnt Cost Efish'nt³

    i know my 07 merc efi 4 stroke woud not accept any props from merc 2 strokes. the spline was completly different.

    brett, you can swap hubs for just about any prop (within reason)
  8. Brett

    Brett > PRO STAFF <

    Cool, I see me and my micrometer wandering around prop shops
    looking for similar size hubs and exhausts. That ought to confuse
    the sales guys. I'm so easily entertained.

  9. TomFL

    TomFL Well-Known Member

    That's what I had always heard as well, but the props are interchangeable between the three motors. Would be worth checking final drive ratios to see how the pitch would work between motors before going further with hub swapping.