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  1. #1
    My name is Sean and I am addicted to STXs smokeysevin's Avatar
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    Doo powered STX-R and STX-15f Builds

    Starting this as a premptive strike and planning thread. I snagged this pair of neglected and nasty salt water skis (2008 rxtx and gtx) about a year ago and am finally getting around to doing something with them.

    I have a spare stx-r hull and my old "nasty" 15f hull I plan to use.

    My original plan was to get the two doo's running as is but after I started cleaning these poor doos up I think its probably better to just yank the motors out and start from square 1 so I know that any corroded or neglected parts are replaced.

    Long term I want a pair of reliable and quick skis that I can hit the starter button and go, change the plugs and change the oil and not stress over.

    I am thinking it will end up similar to this:

    300 charger or x charger on both motors
    external intercooler on both
    run stock electronics with a gps speedo module
    Use doo fuel pump assemblies in kawasaki tanks
    Front mount the battery

    Not sure I will run trim yet, I may try and cobble together a weird hybrid gpr nozzle onto the pump.

    As far as the pump goes I am thinking about a 155mm 250x pump since it drops into the stx pump shoe as long as the seal area is bored out.

    I want to use the kawasaki driveshaft since its easy, robust, I have spares, and the coupler is less picky about alignment. I am in the process of working out a new pto coupler in place of the threaded and splined internal piece of the stock doo setup but another member mentioned that he ran into trouble with the kawasaki coupler fouling on the supercharger.


    That gets us up to speed. The real interesting part is that the 15f hull uses 4 motor mounts and has no inner liner. The stxr hull uses 3 motor mounts like the doo and has an inner liner similar to a gpr.

    Since I have one of each, I will end up with two unique mount setups. Everything else should be about the same.

    The 15f hull will get the co2 trim tab setup I made for my nasty 15f build but both will run similar handling packages.

    The stxr hull will have the full lenght 3 person seat while the 15f will get just the front seat from the later model split seat setup.

    Both hulls will use the stxr style hood.

    Sean


  2. #2
    Kosh's Avatar
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    Looking forward to reading about the journey, let the fun begin.

  3. #3
    steve45's Avatar
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    Sounds interesting!

  4. #4
    My name is Sean and I am addicted to STXs smokeysevin's Avatar
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    Spent some time this morning thinking through the coupler adapter and I am hoping to pick the brains of a few of y'all who are more experienced with the doo pto setup. I made a quick drawing of the proposed adapter shaft with some rough caliper measurements.

    Things to measure/confirm:
    Pto bellow seal position, retention, and actual diameter
    Overall length
    Torque spec
    Material
    Hardness
    Necessary vs unneeded features


    I should note, these are preliminary so use at your own risk. More specifically, they were measured with harbor freight calipers so the dims are plus or minus 17 inches. I am not particularly happy with the shoulder width where the kawasaki coupler stops when threaded on, its a little more narrow that I want but I am trying to use the stock DOO pto seal so the OD of the shaft has to fit the same as stock.



    Questions:

    Does the crank feed oil into the pto shaft to lube the driveshaft splines? Specifically, are the 3 ports on the pto coupler inlets or outlets?
    Can the spiral groove on the exterior of the shaft be omitted?


    Thanks,

    Sean
    Attached Thumbnails Attached Thumbnails Click image for larger version. 

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    Last edited by smokeysevin; 09-18-2019 at 12:16 PM.

  5. #5
    My name is Sean and I am addicted to STXs smokeysevin's Avatar
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    Just a few pictures for reference.

    Click image for larger version. 

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    Sean
    Last edited by smokeysevin; 09-18-2019 at 12:15 PM.

  6. #6
    Bob 1tommygunner1927's Avatar
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    Quote Originally Posted by smokeysevin View Post



    Questions:

    Does the crank feed oil into the pto shaft to lube the driveshaft splines? Specifically, are the 3 ports on the pto coupler inlets or outlets?
    Can the spiral groove on the exterior of the shaft be omitted?


    Thanks,

    Sean

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  8. #7
    My name is Sean and I am addicted to STXs smokeysevin's Avatar
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    Quote Originally Posted by 1tommygunner1927 View Post
    Interesting, thanks so much for posting.

    Given that the crank does feed oil to the pto I am not sure I want to block it off completely but I also don't want to run it unrestricted in case it drops the pressure of the rest of the system.

    I need to do some thinking on how to get close to the same restriction.

    I am probably over analyzing it but if I am going to make the part I want it to be right the first time.

    Sean

  9. #8
    This is how I run a jetski shop in the desert nmpeter's Avatar
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    on the 4-tec the splines at the pto are straight, unlike the pto on other models which are "footballs", to allow for engine jinking on the driveline. That's why engine alignment is a critical issue on 4-tecs.

    You get some play with rubber mounted driveshaft bearing on the midwall, but I'd say without measurement it would be about half of what seadoo supplies with their setup. You'll need to modify an engine alignment tool plate to fit the 15f pump shoe that will allow to to get the pto and midwall in perfect alignment with the center line of the jetpump so you can get the midwall bearing and the pump and the pto is close alignment

    The straight spline setup is the reason for the somewhat forced lubrication system and oil slinger system

    I would say that a close examination of the seadoo pto/driveshaft bearing/seal affair will give the hints needed to adapter the k driveshaft to the seadoo pto and maintain the integrity of the spline oiler

    as you've noticed, the clearances between the pto assembly and the blower are close, so close in fact that when replacing the pto bearing assembly its noted in the manual to position the assembly after replacement a certain way to avoid contact with the bottom have of the blower. The rubber flap that protects the top of the driveshaft needs a close look for your setup to avoid interference

    with the tooling at your disposal I don't see this being much of a problem now that visualization was made possible by the videos

    in the big picture, its clear to me at least that the kawasaki driveshaft system seems to be less prone to trouble with the main point of failure being the midwall bearing which is kinda easy to deal with compared to the seadoo pto seal.carbon ring setup, with the sole exception of having to lift the kawasaki engine to get the driveshaft out. I'd call it a toss up given the amount of trouble I've dealt with getting the seadoo driveshaft "tophat"off the driveshaft on older neglected skis

    and no, you are not over analyzing it. I am. I'd be looking at how the Kawasaki driveshaft coupler will work when mated with the seadoo PTO when the jinking engine is in play, modifications to the seadoo pto cover for some extra support to the bearing carrier assembly might be needed to prevent premature spline failure due to side loading given the reduced distance between the pto and midwall on the 15f hull compared to the floating setup on the seadoo with the entire length of the driveshaft and the football shaped driveshaft splines allowing for the required deflection

    throw all of this in your blender and see if the sauce that comes out is understandable

    and as we say in the city of elephant butte:

    "let the fun begin...."


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  11. #9
    My name is Sean and I am addicted to STXs smokeysevin's Avatar
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    I don't plan on using the pto splines at all. There is enough slop in them that if they weren't supported by the carrier and the the pump the end would flail around. The kawasaki coupler would make that worse since its lots of unsupported mass.

    I gave some thought to just having an adapter pressed into the pto sleeve on the doo crank and welded in place but I was worried about balancing issues.

    The drawing I made above completely eliminates the stock doo pto sleeve by threading onto the crank in its place. I drew it up to use the same oddball bearing and bellows seal setup.

    My big concern is getting the shaft adapter setup so that I can still seal the oil in without making it into a weak point. The good news is that it looks like the stx thread and shaft size are really close in size to the narrow portion of the doo driveshaft.

    I hope to get the stock doo parts inspected this week or next at the materials lab at work so I can spec a good material for the new parts.

    One problem area I have already found is that the seadoo crank thread is an oddball m27 ◊ 2.5 which appears not to exist in tap form. The id is pretty narrow so I wouldn't be surprised if I need to get a custom cutter made to fit.

    On the oil side of things, since I don't know the oil volume that the stock part flows, I will probably need to rig up some test to find out. Its probably okay to just block the port but I am hesitant to just test it. I could probably get reasonably close with a cfd study but I am not super confident on accurately measuing the clearances in the pto sleeve.

    Sean

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  13. #10
    This is how I run a jetski shop in the desert nmpeter's Avatar
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    there are a couple of seadoo 4tec models where I believe the driveshaft actually threads into the PTO, I believe it was the 10 or 11 models years. Have never had to deal with one, but I've read about them. I'm sure you'll know about those shortly

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