Retrofitting 6.75hp Briggs To Sea King Lower

Discussion in 'DIY Marinizing' started by YOSHIBG, May 25, 2007.

  1. YOSHIBG
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    YOSHIBG Junior Member

    Hello All, This Is My First Post, Hope It Works Ok. I Have An Old 7 Hp Montgomery Wards Sea King That The Powerhead Is Bad. I Want To Replace It With A 6.75hp Briggs Vertical I Have. I Hope Someone Can Help Guide Me. How Would I Hook Up Some Sort Of Centrifugal Clutch Between The Shafts So As To Not Be Direct Driven? It Appeares My Only Option Is To Have One Custom Made For $150.00, Which Defeats The Purpose. Any Help Would Be Appreciated...
    Thanks
     
  2. alan white
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    alan white Senior Member

    If you can put a pulley on the prop shaft down, and one on the engine, offset by a couple of inches, you could have an idler pulley with a lever (pulley inside the belt, not outside, otherwise can't have shafts close enough).
    use a spring to force the idler into neutral, and a notch in the lever to catch a detent and hold in forward. Make detent adjustable.
    The belt will act as a clutch, will cost a few dollars, pulleys won't be much either, will allow different ratios to be tried out (Briggs will be higher torque, lower RPM than original).
    I picture a pair of plates, 1/4"-3/8" aluminum, one to mount to engine, one to lower unit, with maybe an inch and a half between them, spacers between with bolts inside them holding the plates on. The pulleys and idler go between, with idler pivot and arm also between. All drill press and table saw work, and maybe a couple of square feet of aluminum.
     
  3. YOSHIBG
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    YOSHIBG Junior Member

    That Sounds Good

    What About The Same Setup But With Some Sort Of Centrifugal Clutch (say Off A Go-cart Set Up)? Would That Work? How Would I Know About What Rpm's The Clutch Engaged?
     
  4. alan white
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    alan white Senior Member

    The clutch will work of course, and without the idler, it's simpler. Can you save the one it had? RPM is what engages the clutch, regardless of power. Chain can be used (but a belt is cleaner). The clutch of any four stroke Briggs should be based on 3600 RPM governed redline. Your engine will accept any clutch with (is this right?) a 3/4" shaft that came off a 4 stroke flathead and possibly some OHV models (though I think they go higher--- but still should work.
    You can change the springs in the clutch too, easily.
    Those clutches must engage at around 1000 RPM, just a guess. Disadvantage against idler/belt is you can't putt-putt, which gives amazing fuel economy and surprising speed depending on hull type.
    Another issue is the prop, which is designed for higher RPMs, maybe 5000?
    Rather than change it, figure the difference between the designed RPM and the 3600 of the Briggs. My guess is you want to speed it up by at least 1.5.
     
  5. TerryKing
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    TerryKing On The Water SOON

    Alan has given you some good perspective...

    Question: What did the original engine have??? Forward-neutral-reverse, or just "start and Run"??
     
  6. YOSHIBG
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    YOSHIBG Junior Member

    The Original Engine Had

    Only Forward, And Some Sort Of Inline Clutch, That Doesn't Work Anymore. To Be Completely Honest, It Never Ran For Me, It May Have Been Direct Driven. I'm Thinking Of Going The Centrifugal Clutch Route, Belt Driven - Only Now I Have To Determine What Size Pulley To Put On The Lower Unit Shaft To Have The Correct Ratio. This Is Confusing For Me.
     
  7. YOSHIBG
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    YOSHIBG Junior Member

    Ok I Just Looked...

    It Had Forward And Neutral, To Put It In Forward, Had To Pull A Lever, That Apparently Engaged It Into Forward Somehow...does This Help? Clinton Engine Model # K7002107a
     
  8. alan white
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    alan white Senior Member

    No kidding--- a Clinton. There's an old name. Clinton made a lot of two cycle engines way back. The lower unit pulley might want to be half the size of the engine pulley. I used to rebuild them as a teen and run them on all kinds of contraptions.
    There will be someone here who is good with props. The prop should be marked with two numbers. find the numbers and hen see how many turns of the lower unit shaft equal one turn of the prop. With that, and the 3600 RPM engine max, we should arrive at the right pulley sizes.
     
  9. TerryKing
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    TerryKing On The Water SOON

    It HAD a clutch??

    So it had a 'clutch', probably a typical outboard 'dog clutch' which is OK because of the propeller slip.

    So maybe you don't NEED a clutch, especially as you can probably idle even lower than the original....
     
  10. YOSHIBG
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    YOSHIBG Junior Member

    Is There A Way To Post Pictures Here

    If So I Can Post A Pic Of The "clutch" And Let You Guys See It...
     
  11. alan white
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    alan white Senior Member

    True, if there's a clutch, it might be functional. However, once the ratio is changed to speed up the lower unit shaft, the clutch will again work at the same speed--- that is if you increase the speed by pulleys, which makes sense given a two cycle is a much higher RPM engine than a four cycle.
    I'm imagining a dog clutch now, never having seen one. I imagine two arms held in by springs on fixed pivots. The end of each arm has a semi-circular knob that goes outward at a certain threshold RPM. Around this, a drum has a scalloped inner surface. There is also a rubber damper built in between two parts that interlock like a typical shaft coupler. The rubber takes up the shock of engagement enough to soft-start the shaft to the prop.
     
  12. YOSHIBG
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    YOSHIBG Junior Member

    Here Are Some Pics...

    Of The Clutch - I Think It's Not As Complicated As Some May Thing. Really, It May Just Be A Shaft Adapter...
     

    Attached Files:

  13. YOSHIBG
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    YOSHIBG Junior Member

    Oh, I Forgot To Add. There Are No Numbers On The Prop - But 1 1/2 Turns On The Shaft Equals One Turn Of The Prop
     
  14. alan white
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    alan white Senior Member

    Not what I expected. A shaft coupling wouldn't have a square hole in the side with what looks like a nub with a shiny surface inside.. Must be a very simple clutch, but looks a bit dry/corroded. Should be self-explanatory, once free and lubed.

    where's Terry?
     

  15. YOSHIBG
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    YOSHIBG Junior Member

    Let Me Tell You More

    About This "clutch". If You Try To Spin It Counter Clockwise, Holding The Top And Bottom, Only The Top Spins. Clockwise, The Entire Thing Spins, Which Is The Correct Direction To Go Forward. The Little Nub, I Don't Know What That Is, I Want To Take It Apart, But Can't Figure Out How Without Tearing It Up. Some One With Some Knowledge Of The Montgomery Ward Sea Kings Would Be Very Helpful.
     
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