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  1. #1
    madtom's Avatar
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    My winter rebuild project 2003 12f STX

    looking to start the rebuild of the " my second Ski" 12f 03STX this winter. I was wondering if anyone has a done a guide or illustrated an engine rebuilds of a 12f or 15f? I know most of this stuff is almost a direct linkage to the street ninja motors. just want some pointers on engine tear down and assembly that the factory may have left out of the service manuals (which I have).

    i have noticed some trying to escape using the wonderful guaranteed to quit working at some time kawa dash meter. I used a 5 dollar polarized filter for a phone and some shipping tape to fix the dash on the 900.

    I have seen no successes other than some of smokesevin's builds using MS or standalone on some of his kawa motors. I am not that gifted so unless someone shows me a way to use the ski with only analog gauges then i am stuck with the factory dash it has to get some data from the ecu as there are some things displayed that have no wires going to the dash.


    I know the ski should be reliable once i get it back to operational standards.....my boys put like 90 new hours on the 900 during the summer months(i live on the water) and all it really got was a good breakdown/cleaning/new rings/and a pump repair to bring it up to speed.... here is a pict of the 900 after it running again.



    I am trying to do this for the 12f and want the pride of doing it myself and trying to keep what i put into it under kelly BB value lol (only spent 200 for the ski so a budget of about 2200 to get it up and running.)


    history of the ski...bought 2 skis for dirt cheap as second owner had no time or desire to spend time figuring out what was wrong (paid more for the new trailer lol)

    the 12f only has 65 hours or so showing on the part of the meter that works. first owner didn't understand the meaning of preventative maintenance and ran the ski in brackish water along the Chesapeake along with sand from beachy areas (I pulled like a whole island worth of sand and calicfied salt out of the 900stx jugs on the other ski that was overheating with only 50 hours on the dash)


    I know that somewhere between the cooling and lubrication systems on the 12f there has been a breakdown. although i was able to get it to run last year and idle water was able to make it into the sump so the oil turned milky. drained it all out and put new oil back in before i covered it up.

    as for engine electrical the harness and the fuel system are functional so probably only need to put new o-rings into the injectors after cleaning them.

    compression was good so looks like i might be able to skip the pistons and rings if i want to. if i do choose to replace pistons which brands would you recommend ( nothing against SBT just trying to see what else is out there) .

    i have a spare oil cooler to see if the old one has corroded thru that is where the breakdown is I still want to upgrade to the version that mounts on the block as it seems to be fewer things that can go wrong.

    exhaust manifold and 4 into 1 are solid with corrosion so looking for freshwater used manifold on ebay and probably get a new 4 into 1.

    intake side waterpipe on block is earliest configuration and needs to be upgraded.

    will probably pull lower crankcase apart to inspect bearing wear, replace all seals and the oil pump parts.

    plan on replacing timing chain and all guides.

    the head is something im kinda concerned about but until i get it apart i wont know the level of corrosion and blockages of the cooling passages. even if everything checks out a lap job and new vallve stems seals are probably a good investment.

    I plan on using oem gaskets as they seem to have a better track record than some of the others out there.

    i plan on redoing the pump and impeller while the engine is out and all cooling lines so i should be good for a few years.

    Tom
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  2. #2
    steve45's Avatar
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    You had me wondering with that picture of the 900 engine!

  3. #3

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    If the motor runs and has good compression, why tear it down? It's possible that the cause of water in the oil is not due to anything inside the engine. Water can get into the oil in a variety of ways, including water in the fuel tank, water in the intake manifold and corrosion in the exhaust manifold. If you can solve that problem without an engine re-build, then you'd be better off just fixing the problem and using the ski until you actually need to re-build.

    Even if you decide to go for the re-build, you should first figure out exactly where the water is coming from. If you don't you may end up dumping water into your newly re-built motor.

    For my first 15f re-build, the best tool was the digital camera. I took many photos at each step of the tear-down. Re-assembly was easy using the pics as a reference. I've built two more since then using the same pics as needed.

  4. #4

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    What was the point of that filter on the dash? If the plastic is scratched and cloudy, there's a better solution. You can get one of those headlight cleaning kits. I cleaned up a Yamaha dash by wet-sanding with 600 grit sandpaper and then using polishing compound to buff it out. Looked almost as good as new.

  5. #5
    Pain is fear leaving your body.... rlovebk's Avatar
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    Chances are the exhaust manifold is probably where your water is entering your motor. There is a nipple down low that degrades and does this at the collector.
    Cool project. I have many parts for 12F motors but unfortunately no exhaust parts. They tend to be pricey as there are not many but that is just supply/demand on the used market.
    Good luck and PM me if you need anything.

  6. #6
    madtom's Avatar
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    update to winter project 03 12F

    So a little update on the project.
    I had known bad parts on order thru the winter. Pulled the engine last week. Oil cooler 95% clogged, stator cover completely solid between corrosion / salt / sand, Exhaust manifold corroded thru.

    My water in the oil was coming from the o-ring in the oil cooler.... it had no where else to go. bad design water pipe on intake side clogged and corroded... had to drill out what was left and pick the pieces out with dental pick..... I cleaned all of the clogged areas and the engine was pretty clear and has good water flow..... i guess the beach sand all stopped at the ends of the cooling system.

    Engine is almost all back together now. upgraded to a oil filter mount cooler from a 05. I used the old allen plug from the end of corroded water pipe to plug old oil pressure sensor threaded hole (same threading 1/8 BSPT i think).

    I got a friend to weld a new ring on the muffler box to fix that corroded mess. the sand and junk was even in the waterbox. The old 4 into one wasn't worth saving so cleaning up a used one now. going to do the waterbox mod and pull the back one.

    I found melted wire on electrical harness in 3 places so replacing that also. I pressure washed out the hull today and pulled fuel tank to put in 05 12f 16 gal tank. There was all kind of crud in the bottom of the original tank. Fuel was so old it was yellow in color.

    The in tank regulator is corroded beyond saving but the fuel pump was just fixed so going to upgrade to a FPR off of the fuel rail.

    Iam awaiting oem bearing and seals to come in so i can rebuild thru hull bearing and pump.

    last decision will be on whether the upgrade the thru hull water lines to something better than plastic as i dont want to do this again in a couple of years.

    So the PO's no preventative maintenance program has left me a lot to do but the engine seems solid on the inside as it only has like 55 hours on the clock.

    the service manuals and the forums have been a godsend for figuring all of this out.... of course finding actual 6mm and 7.5 mm high pressure fuel lines without doing the 50 bucks for 3 feet OEM can be solved by using the following import car web pages for a little better pricing.

    https://www.belmetric.com

    https://www.midwest-bayless.com



    I will send pictures once it starts getting put back together. The 02 900STX has already started the season strong.... and I didn't even have to change the plugs... still screams along.

    Now a question for the crowd. if this ski will be used to tow kids around will it help to bump up the FPR to about 45PSI to make it run a little richer? or just leave it at 43PSI ? Not planning on doing any timing bump just want to make sure it is getting enough fuel on the map to pull about 250-300 pounds on a 3 person float.


    tom

  7. #7
    madtom's Avatar
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    the polarized filter inside the meter is burned out.... the 10$ fix gets taped on the outside and you can see the numbers again vs shelling out 1K$ for a new or used meter....

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  9. #8
    madtom's Avatar
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    So I installed new water pipe on intake side of block today. what is interesting is there is no torque values i could find with the manual. so I used values posted for stator cover seeing that bolt is same size.

    Awaiting the rest of parts to start putting all of this together again. Original cost for me for this ski was only $200 so with the $800 invested so far thanks to the benefits of Ebay, I am still on the positive side of this money pit..... as my grandfather always said the two most favorite days with your boat are the day you buy it and the day you sell it.... everything in between involves money going from your pocket to someone else.

    hopefully will be able to start it up next week after getting engine back into hull..

  10. #9
    Bucky STX-15F's Avatar
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    nice work, keep us informed.

  11. #10
    madtom's Avatar
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    Today's update,

    Was able to finish the wiring harness tonight and start the fuel tank swap. Putting the 51004-3739 16+ gallon tank in place of the original 14.5 gallon from the 03. Still waiting for OEM driveshaft bearing and seals to come in. Since the engine is out just going to replace parts while I can....the old one is now 16 years old.

    tomorrow will be fuel system day

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