Retrofitting 6.75hp Briggs To Sea King Lower

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

  1. alan white
    Joined: Mar 2007
    Posts: 3,731
    Likes: 121, Points: 0, Legacy Rep: 1404
    Location: maine

    alan white Senior Member

    Yeah, that's a clutch. Very simple, but as said by Terry, props offer little startup resistence. The long shaft down must torque around like a torsion bar too to take up the load. Are you aware of the relative rotation directions of the two engines? The Briggs will be clockwise viewed from shaft output, and all you need to do is to look at the prop to know what direction the engine should go.

    Any case, a soaking in kerosene wouldn't hurt, and blow out clean and dry, then grease. That aluminum looks pretty eaten up, by the way. Maybe someone here knows how to seal it while you're at it.
     
  2. YOSHIBG
    Joined: May 2007
    Posts: 11
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: CORSICANA,TX

    YOSHIBG Junior Member

    Yes, I Checked And The Rotations Are The Same...do You Think This Clutch Is Rpm Engaged? I Recall There Was A Lever You Would Pull To Put It Into Forward. Is There A Way To Take It Apart And Clean It? If It Would Work For Me, Then That Would Save $$ And All I Would Have To Do Is The Pulley Set Up
     
  3. alan white
    Joined: Mar 2007
    Posts: 3,731
    Likes: 121, Points: 0, Legacy Rep: 1404
    Location: maine

    alan white Senior Member

    Right. There is a relationship between the clutch and the lever. So the relationship is through an increase in RPM unless the lever also mechanically effects the clutch (by raising or lowering a sleeve around the clutch and causing a part of the clutch to be thus effected, for example).
    Again, common sense will apply. Any lever that would effect the clutch would be beefy and have a decent sized hole for the attachment of a rod.
    Or, if centrifugal, there would only be a small hole for a light rod to the carburator only. And that thin rod or mechanism must now be altered to make the new engine do the same thing as the old one. The choke is easier, since the old cover won't fit now.
    You really should be able to play with the clutch and maybe hook a drill up to it while its on the lower unit, COUNTERCLOCKWISE because you're looking backwards at it, meaning run the drill (hopefully a 1750 RPM reversing drill, plug in type) in reverse.
    Do you still have the old engine and paraphenalia?
     
  4. YOSHIBG
    Joined: May 2007
    Posts: 11
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: CORSICANA,TX

    YOSHIBG Junior Member

    ok, if you pick the engine up and hold it over your head, looking at the shaft, then it is counterclockwise. But looking down at the shaft going to the propeller, it needs to spin clockwise to spin the propeller the correct direction. does this sound correct? I took the old "clutch" apart and it's gone. basically rusted through, then I broke it worse taking it apart. So that being said, what kind of go cart belt clutch should i but. the shaft is 7/8" by the way. also, i am kinda worried about when the clutch kicks in, it putting too much torque on the shaft and propeller getting them started.
     
  5. alan white
    Joined: Mar 2007
    Posts: 3,731
    Likes: 121, Points: 0, Legacy Rep: 1404
    Location: maine

    alan white Senior Member

    It sounds correct. Seems almost all lawnmower type engines are CCW.
    You should mount the clutch on the engine, so either 3/4" or 7/8" is my guess of the diameter, so long as it's a straight shaft and not tapered with a threaded end. Either that or find a replacement for the original clutch.
    The clutch, if a common centrifugal one, has to have a pulley and not a sprocket, and while go-carts usually use chains, many kinds of power equipment use belts, so look into getting a replacement clutch for a piece of power equipment that uses the engine you have. Briggs makes an outboard line too, and perhaps something they use will work, don't know.
    The lower unit shaft is another story. It would be wise if you could re-use the part of the broken clutch that connects to the lower unit shaft, if sound.
    Then you have to adapt that to a common 5/8" jackshaft. If the original lower case shaft used the engine to carry the upper end of the shaft, meaning no bearing is at the top of the lower case inside, it will be easier, because the jackshaft will align the LC shaft with a solid connection. If an inside bearing is there, it will require a soft fit to the jackshaft so as not to stress it. What is needed then is a rubber-isolation type coupling, something used a lot between electric motors and pumps when inline.
    The lower half of the rubber damped coupling would have to sleeve around a 5/8" section of shafting that is welded to the top of the clutch part that fits the LC shaft. So what you'd see before adding the mounting plates would be a stump of 5/8" shaft sticking out a couple of inches--- enough to slip the lower half of the isolation coupling down onto it. It can be below the lower mounting plate by a little bit, because the "jackshaft" can have bearings mounted on each of two plates and also pass through the bottom plate a little ways, enough to almost meet the shaft coming up (1/4--1/2" inch clearance is fine). So the clutch, belt, and pulley are all sandwiched between two thick aluminum plates. The "jackshaft" is coaxial to the LC shaft.
    All that's left is to tension the belt, and I suggest the idler be a big 1/2" wide ball bearing outside of the belt. That would need an arm of 1/2"x 1 1/2" steel and a shaft stub welded to the flat of one end, and a hole in the shaft for a cotter pin near the top of the stub shaft. Its length would allow it to swing against the side of the belt on a bolt pivot, and a spring to hook the arm to pull it inward.
     
  6. YOSHIBG
    Joined: May 2007
    Posts: 11
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: CORSICANA,TX

    YOSHIBG Junior Member

    that sound possible,

    i think i'll look farther into finding a clutch now...when i finish i'll post pictures. any one else care to give two cents?
     
  7. Capt-Ron
    Joined: Jul 2008
    Posts: 6
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: SC Lowcountry

    Capt-Ron Junior Member

    I do believe that the item pictured is a spring loaded shock absorbing adapter. I've run and worked on a few of this size/year motor and most were direct drive.

    Good Luck,
    Capt-Ron
     
  8. ben2go
    Joined: Jul 2008
    Posts: 183
    Likes: 4, Points: 18, Legacy Rep: 13
    Location: Upstate, South Carolina,USA

    ben2go Boat Builder Wanna Be

    I know I'm bringing up an old thread.There is a big rpm issue with this.The original 2 stroke rpm were between 5000 and 7000 rpm.The new engine spins 3600 rpm max.The prop will turn at half it's rated speed.It not very effiecent but it will work.Stepping up the rpm through gears or pulleys would help.If the unit had a forward/neutral/reverse lower unit a clutch would be counter productive.The lower unit will need to be spinning in order for gears to mesh while shifting.If it's a direct drive,then a clutch would be a lot of help at start up and during idle.Just remember that slow speed operation may be reduced.
     
  9. ned L
    Joined: Nov 2008
    Posts: 76
    Likes: 7, Points: 8, Legacy Rep: 105
    Location: N.E. Connecticut

    ned L Junior Member

    Again, yes the topic is getting old.... That is a clutch. The way it works is that there is a coil spring inside the metal shell , the spring nautally has an inside diameter smaller than the upper & lower shafts so that it couples the shafts together, making both shafts turn together, and the torque from the engine tightens the spring even more (a bit like how 'Chinese handcuffs' work on your fingers). When you want to go into neutral the shift lever has a pawl which come into line with that small square end of the coil sping (visible in the picture) and forces the spring to stop spinning, and at the same time forces the spring to open up in diameter enough so that it no longer grabs onto the shafts, allowing the crank shaft to turn while the prop shaft doesn't turn.
     
  10. pistnbroke
    Joined: Jan 2009
    Posts: 1,405
    Likes: 33, Points: 48, Legacy Rep: 404
    Location: Noosa.Australia where god kissed the earth.

    pistnbroke I try

    the trick with all these engine conversions is to take the crankshaft out of the old engine and cut the end off with the mating spline...you weld or collar this to the new engine crank and that mates the two together...then you need spacers to positon the engine in place atop the old outboard
     
  11. ehuntersullivan
    Joined: Mar 2009
    Posts: 1
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: lansing michigan

    ehuntersullivan New Member

    sea king motor

    hello i have a non running old sea king motor and lower end it is complete i bought it from a garage sale guessing i can make it work
    but if it would serve you better then let me know
    ehuntersullivan@yahoo.com
     
  12. ben2go
    Joined: Jul 2008
    Posts: 183
    Likes: 4, Points: 18, Legacy Rep: 13
    Location: Upstate, South Carolina,USA

    ben2go Boat Builder Wanna Be

    You can make a plate and adapter to mount a small push mower engine in place of the power head.
     

  13. pistnbroke
    Joined: Jan 2009
    Posts: 1,405
    Likes: 33, Points: 48, Legacy Rep: 404
    Location: Noosa.Australia where god kissed the earth.

    pistnbroke I try

    Thanks ehuntersullivan but I think you did not spot I was in australia !!!
    We got lots of old motors here ....if you are adding a lawnmower motor then
    1/ ensure you have the end of the engine crankshaft with the internal spline to make your adaptor from. Make the adaptor to the drive shaft first and then with the motor balaced on the top take measurements for the plate or spacers .. If you dont use a splined adaptor then you cannot lift the motor off.
    2/ make sure it has FNR gears and a 3..75 B & S drives a 8 x7.5 fine


    Photo is of a 4hp suzuki I adapted ..sorry the photo is the wrong way
     

    Attached Files:

Forum posts represent the experience, opinion, and view of individual users. Boat Design Net does not necessarily endorse nor share the view of each individual post.
When making potentially dangerous or financial decisions, always employ and consult appropriate professionals. Your circumstances or experience may be different.