Doo powered Kawasaki STX Build (STX-RXT-X)

[smokeysevin]

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 and I have a spare STX hull I plan to use so you can guess where this is going (nowhere fast).

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 reliable and quick ski that I can hit the starter button and go, change the plugs and change the oil and not stress over.

As it sits now, the build looks like this;

2009 RXT-X 255 motor and electronics
Frozen Boost External Intercooler
2009 RXT-X Driveshaft
2009 RXT-X 159MM pump and nozzles on custom Kawasaki pump shoe to Seadoo jet pump adapter
Updated carbon seal, bellows, and hat
Stock rebuilt VTS Unit
R&D Rideplate
R&D Sponsons
R&D Intake Grate
Custom Kawasaki Steering Stem to Seadoo X-Ski bar adapter
Stock Kawasaki Steering and Reverse Cables (steering cable in stock position, reverse cable is moved to left side.

Sean

[Kosh]

Looking forward to reading about the journey, let the fun begin.

[steve45]

Sounds interesting!

[smokeysevin]

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

[smokeysevin]

Just a few pictures for reference.









Sean

[1tommygunner1927]

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

https://youtu.be/C7zDoIy_QqQ

[smokeysevin]

https://youtu.be/C7zDoIy_QqQ

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

[nmpeter]

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...."

[smokeysevin]

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 ?ù 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

[nmpeter]

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

[1tommygunner1927]

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

I suggest contacting the expert GPR conversion builders as they could provide useful info on mounts, hull cuts, driveline, pumps, and other things. In my opinion, leave the oil cooler as is, leave the PTO coupler and bearing/seal as is, and possibly use other seadoo parts.

[smokeysevin]

I suggest contacting the expert GPR conversion builders as they could provide useful info on mounts, hull cuts, driveline, pumps, and other things. In my opinion, leave the oil cooler as is, leave the PTO coupler and bearing/seal as is, and possibly use other seadoo parts.

I am not sure yet if I will even need to move the cooler but hopefully I can avoid cutting the hull or moving it.

Regarding the coupler and shaft, another member mentioned that the yamaha vx110 shaft fits the kawasaki pump splines so that may be an option but I have not confirmed that yet. I did pickup a yamaha midshaft and coupler assembly but I would rather use the kawasaki parts for ease of alignment and the fact I have all them already.

To my mind (biased towards the kawasaki setup since that is what I am familiar with) the kawasaki coupler makes the most sense from a reliability and ease of setup perspective. I am happy to consider other options though. By no means am I an expert on the 4-tec which is why I am asking for help. I appreciate it greatly everyone.

Sean

[smokeysevin]

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

Do you know offhand which models they are?

Kawasaki uses a stub shaft on the stator side that goes from the crank to the pto coupler so its not groundbreaking.

Sean

[1tommygunner1927]

I am not sure yet if I will even need to move the cooler but hopefully I can avoid cutting the hull or moving it.

Regarding the coupler and shaft, another member mentioned that the yamaha vx110 shaft fits the kawasaki pump splines so that may be an option but I have not confirmed that yet. I did pickup a yamaha midshaft and coupler assembly but I would rather use the kawasaki parts for ease of alignment and the fact I have all them already.

To my mind (biased towards the kawasaki setup since that is what I am familiar with) the kawasaki coupler makes the most sense from a reliability and ease of setup perspective. I am happy to consider other options though. By no means am I an expert on the 4-tec which is why I am asking for help. I appreciate it greatly everyone.

Sean

Easyrider has a stub shaft....

[raven007]

The splines fit the early VX110 pump, the one that is built like a kawasaki and seadoo without the driveshaft attached. Source: Me! I used the spline tool to swap an impeller and it fit nice and snug.

I would probably make a stub shaft (cut down a driveshaft?) to go in the stupid seadoo engine spline with a kawasaki coupler threaded on, then use the kawasaki thru hull and driveshaft. I think this is the road you are headed down?

I still plan to try the vx110 pump on a 15f because vx110 pumps are way cheaper than 155mm kawasaki pumps. I think there is enough room for the transom plate to fit the kawasaki hull. But I haven't investigated what that does with regard to rideplates and intake grates. Both would need work.