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Thread: Yamaha 115 4 Stroke Jet to prop conversion

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    Default Yamaha 115 4 Stroke Jet to prop conversion

    Main motor:
    2006 Yamaha F115TJRD
    115 horsepower (80 at the jet output)

    Question is what do I need to do to convert my jet drive to a prop

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    A prop Lower unit! and probably the shift mechanism... If it's not there already, ya gotta remove the power head to install / remove. ouch$$ other wise a prop lower will bolt right up

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    the hard part is finding the prop lower unit. I have a buddy that has the same motor and he has been looking for quite some time for a used lower unit and not been able to find one. Otherwise the switch over is rather simple. i personally have a merc and it only takes me 20 min to change between the prop or jet. there are a few extra cables that are needed but not too be of a deal.

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    Thanks for the reply.

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    We end up with those lower units from Jet conversions fairly often, occasionally have used ones, but mostly new take-off's. The last F115Jet from Yamaha still had the shift shaft in the motor, so I wouldn't think you'll need to put one of those in. After that, is should be an easy swap between the two.
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  6. #6

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    No body has mentioned that the engine will need to be lowered when adding the prop. I had a Yamaha 175 hp and would switch between prop/jet units several times a season and used a combination hydraulic likt and a bay kit adapter. You can accompish this by either unbolting the engine and movnig it up/down (requres 2 sets mounting holes) which is a pain or you can add a high lift adapter to raise/lower the engine with electric/manual hydraulics. I think you need about 6" of travel to interchange between prop/jet and there are a few of the lifts that have that range of travel. Or there is a bay adapter kit which is an insert between the engine and lower prop unit which eliminates having to raise/lower the engine. You will need to extend the drive shaft if you use the bay adapter.

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    This is true, when you put that lower unit on, it will be 5-6 inches too high to run. The bay kit comes with all the extensions you need for driveshaft, water tube, shift shaft and housing, plus longer bolts. These will still leave you about an inch or so high, but some boats can run with that, some can't. In that case moving the motor mounting down one or two bolt holes can do the trick.
    Casey, Rocky's Marine
    www.rockysmarine.com

    Yamaha Outboards, Hewescraft, Wooldridge, SeaArk, G3, Lund, Garmin

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    Another thing to consider if using a lift is the setback, which is typically about 5", maybe not a big deal on bigger boats with wide bottoms. But short narrow hulls can be affected negatively, the boat will set another 3-4 inches in the water at rest and will take longer to get on step. If your hull has a tunnel that will need to be extended to perform well.

    When I got my current boat setup, I intially just used the jet and thought I would never go to prop, now that I have made the conversion I am glad I did, but it did take a a few steps to get it right, I added some floatation pods to alleviate the set back of the motor, extended the tunnel and used a power trans lift which will allow the conversion w/o a bay kit.

    if you could just use a bay kit that would be cool and eliminate the expense weight and setback of the lift, however the lift does give you a lot of trimming adjustments.

    If the bay kit works but is just a little short you may be able to compensate for that with a cavitation plate, I have been using one from Permatrim and it has worked very well. http://www.permatrims.com/
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    I have a Wooldridge AK II with both lower units and the bay kit- the previous owner said that he couldn't leave the motor in one place and run either lower unit? I have a 5"CMC lift I'm planning on installing this weekend- but if I don't need it I'd rather not. Anyone have any experience they can share? Not trying to hijack- figured it's all related- Thanks

  10. #10

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    I ran the CMC lift along with the bay kit. The lift does set the jet foot back off the transome ~5" which can cause the jet to suck soft water. I had a tunnel and never really had problems. You can add some type of extension to the bottom to keep hard water to the jet. The CMC lift was nice with the jet and prop allowing fine tune adjustment. On my boat witht the jet I could drop the lift the jet in smooth water and drop it in chop, eliminating sucking air like you sometimes hear with OB jets when guys are running rapids. Some hard core river runner guys may say I am crazy to set a jet up like I did but it worked and if you go around town and ask the boat shops you will get a different story form every one of them. The main part is to set it up see how it performs and keep making mods till you are happy with it.

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    Quote Originally Posted by Kandiyohi Kid View Post
    I have a Wooldridge AK II with both lower units and the bay kit- the previous owner said that he couldn't leave the motor in one place and run either lower unit? I have a 5"CMC lift I'm planning on installing this weekend- but if I don't need it I'd rather not. Anyone have any experience they can share? Not trying to hijack- figured it's all related- Thanks
    All related and good info, the CMC lift will not have enough adjustment by itself. It will work but you wil still need to use the bay kit when you go to a prop. Bottom line is you need more than 5" of adjustment to be able to get it just right, does the prop lower have a Cavitation plate? I assume the original owner had to lower the motor one set of holes to run the bay kit.......?

    Thats about 3/4" if memory is right, a cav plate will help and may work at that height? If he had to lower 2 sets of holes than you will most likely need the lift as well...
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    Quote Originally Posted by Kandiyohi Kid View Post
    I have a Wooldridge AK II with both lower units and the bay kit- the previous owner said that he couldn't leave the motor in one place and run either lower unit? I have a 5"CMC lift I'm planning on installing this weekend- but if I don't need it I'd rather not. Anyone have any experience they can share? Not trying to hijack- figured it's all related- Thanks
    I have a Wolly AK II and a CMC lift and can go from prop to jet by only using the lift and NOT moving the engine bolts. I ran the setup over 200 hours with both prop and jet.
    "I refuse to let the things I can't do stop me from doing the things I can"

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    Quote Originally Posted by stid2677 View Post
    I have a Wolly AK II and a CMC lift and can go from prop to jet by only using the lift and NOT moving the engine bolts. I ran the setup over 200 hours with both prop and jet.
    Steve, Does your CMC have over 5" of travel? I have never used a CMC, the powertrans I have has over 7", and I will have to measure how much travel I use to make the swap. I know to optimize at both ends its over 5"........? But now you got me wondering....
    Cuz if 5" works he should be able to use the bay extension kit......if everything is set just right....
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    Quote Originally Posted by Akgramps View Post
    Steve, Is your CMC over 5" of travel? I have never used a CMC, the powertrans I have has over 7" and I will have to measure how much travel I use to make the swap. I know to optimize at bothe ends its over 5"........? But now you got me wondering....
    Cuz if 5" works he shpuld be able to use the bay extension kit......if everything is set just right....
    Mine has 5 inches of travel and when I first started I would change it a bolt hole up and down. I got to looking at it with the tunnel, and thought I can run the prop higher, so I tried it and it works fine. Have used it that way now for several years.
    "I refuse to let the things I can't do stop me from doing the things I can"

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    Thanks for all the great information.

    Quote Originally Posted by Simux View Post
    Main motor:
    2006 Yamaha F115TJRD
    115 horsepower (80 at the jet output)

    Question is what do I need to do to convert my jet drive to a prop

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    Default Reversing Bellcrank

    Allows for changing from prop to jet w/o removing the cowling and fooling around with the cables.

    Worked on mine after I got it dialed in, had to make two of them before I got it right.
    DSCF1291.jpgDSCF1289.jpg
    “There is no wealth but life.” John Ruskin

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    Quote Originally Posted by Akgramps View Post
    Allows for changing from prop to jet w/o removing the cowling and fooling around with the cables.

    Worked on mine after I got it dialed in, had to make two of them before I got it right.
    DSCF1291.jpgDSCF1289.jpg
    That's a great idea- does anyone sell a kit like that? That was the slowest part of swapping for me- playing with those cables.

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    I just came into a wooldridge 16.5 xtra plus 115/80 jet, since we live within eyesight of deep water , N.Idaho
    was thinking it would make more sense to have a prop conversion set up...... or sell boat. it only has three seasons on it even though its a 1989
    yamaha 115 et ld jd jet so I'm Leary of selling since it's in such great shape but realistically we would be only using it to beach camp/tube with kids i'd say 80 percent of the time. I realize it's a river boat hull but runs on the lake pretty well.

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