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  1. #1
    burtonrider10022's Avatar
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    Lets play a game: What caused this piston damage?

    Some of you may remember me, I started posting pretty heavily over the winter when I first got the ski (1993 SL750) passed down to me from my Grandmother. I bought a crap-load of parts and was starting to get under way with a 780 and modular pump swap when school started to overwhelm me, and then my Grandmother went into the hospital and has yet to come out. It's been a very hectic last 6 months, and the ski has been set aside. I've made almost zero progress other than relocating it from Lawton, MI to Orland Park, IL, but I still don't have the title in my name (she's not exactly available to fill out the paperwork, and it's obviously not a priority) so I haven't done any work on it.




    Anyways, I was talking to one of my uncles, who told me that when the ski melted the piston, it was discovered to be out of oil. Allegedly the oil buzzer/chirp thing broke, and no one noticed until after the ski started losing power. In a previous thread, I posted the pics and it was diagnosed as a fuel issue, but he also told me that the carburetors were in fact rebuilt within the last few years (he thinks the fuel lines were changed too, but I haven't been able to check yet). So, could this damage possibly be from low oil? Is a simple piston job all this craft needs? Or am I still looking at lines, carbs, and a piston?


    This is all on the CEN piston, as the PTO and MAG both pressure test perfectly @ 120.

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    Also, I'm being told that the cylinders are nickel, and that they can be "re-nicked" which I'm pretty sure isn't true. I know common practice around here is to bore them out, and I think some of the newer Polaris ski's had nickel linings, but I am just looking for some confirmation.


  2. #2
    john zigler's Avatar
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    That is LEAN..... Piston melted at the exh port, from heat.

    you need to go through the fuel system completely. rebuild the carbs again, replace fuel select, lines, and up grade to a triple outlet pump. Check the fuel tank pick ups, and do a leak down test on the motor.

    Your piston is already at 1st over bore, 0.25mm if you cyl is OK, you may not need to bore up, you may be able to hone, and just install a new pistons and rings.

    The Polaris Fuji motors ( yours) is a standard steel bore, NOT a plated bore. You do not plate these.

    Do some searching / reading here on the Fuji fuel issues. Everything you need to know is right here on this site.
    Last edited by K447; 07-06-2013 at 08:14 AM. Reason: edited .025mm to 0.25mm overbore

  3. #3
    Click avatar for tech links/info, donation request K447's Avatar
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    Quote Originally Posted by john zigler View Post
    ... Everything you need to know is right here on this site.
    Start here.

  4. #4
    David Drkvampire2001's Avatar
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    Look at the pics those are rather rusty, how long has the engine been opened up for?

  5. #5
    burtonrider10022's Avatar
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    I know the fuel issues, I already have carb kits, triple output pump, and fuel lines ready to go, but after discovering the oil thing I figured I'd ask.

    As for the rust, the motor was only opened to take those pics and closed again. In the other thread I linked to the rust was discussed and the general concensus sad that the rust was ok as long as it wasn't on the crank.

  6. #6
    David Drkvampire2001's Avatar
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    Quote Originally Posted by burtonrider10022 View Post
    I know the fuel issues, I already have carb kits, triple output pump, and fuel lines ready to go, but after discovering the oil thing I figured I'd ask.

    As for the rust, the motor was only opened to take those pics and closed again. In the other thread I linked to the rust was discussed and the general concensus sad that the rust was ok as long as it wasn't on the crank.
    Good deal then on rust.

  7. #7
    Connecticut CrazyA's Avatar
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    Quote Originally Posted by burtonrider10022 View Post
    I know the fuel issues, I already have carb kits, triple output pump, and fuel lines ready to go, but after discovering the oil thing I figured I'd ask.
    Changing the fuel selector switch on the '93's is critical as well.

  8. #8
    Click avatar for tech links/info, donation request K447's Avatar
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    Quote Originally Posted by CrazyA View Post
    Changing the fuel selector switch on the '93's is critical as well.
    Why so, compared to later years (or even 1992)?

  9. #9
    burtonrider10022's Avatar
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    Hmm... ok. I remember reading about a SeaDoo or Yammy selector switch working almost perfectly (except backwards, IIRC).

  10. #10
    Connecticut CrazyA's Avatar
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    Quote Originally Posted by K447 View Post
    Quote Originally Posted by CrazyA View Post
    Changing the fuel selector switch on the '93's is critical as well.
    Why so, compared to later years (or even 1992)?
    Because a 1993 SL 750 is what we're discussing.

    I didn't compare it to any other years so your question confuses me.

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