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  1. #1

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    Question 1996 SLT 780 Winter Project

    I recently purchased a 1996 SLT780 (from Indiana/Michigan)for a winter project. I don't have any kind of maintenance history on it. This is my first jetski but I have had numerous boats in the past. The MFD indicates 189 hours and the compression is 135 - 135 - 58. I removed the cylinder heads and found the PTO piston cratered (no hole) and definitely leaking between the piston and the rings. The cylinder is also scored and will need to be bored. The other two cylinders look fine other than they look to have been running very lean (piston tops almost completely black). All of them measure to the stock bore specifications.

    I plan on fixing the bad cylinder, rebuilding the fuel pump & carbs, and checking the whole thing for air leaks over the winter. My questions are:
    • Can I just have one cylinder bored oversize, leaving the other two with the stock bore as is? The OCD in me is telling me that they all need to be the same but I couldn't find any posts on the subject.
    • Should I repair the cylinder without cracking open the crankcase (assuming I find no leaks at the crank seals)? I'm guessing that all of the piston bits exited through the exhaust.
    • Would it be possible for an engine with 189 hours to show no signs of wear (on the two good cylinders)? This is assuming that this is the original MFD.
    • Are there any tell-tale signs that an engine has been rebuilt in the past? The reason that I am asking is that the cen and mag cylinders both have the exact same casting marks on the heads but the pto head has a slightly smaller "B" on the right side and a "2" on the left side where the other two have "3"s.
    • Do all models in the same year have the same MFD installed? The reason I'm asking is that the one on my SLT has a trim indicator on the top of the screen. I wasn't sure if this was standard even though the SLT does not have the trim feature.
    Thanks!


  2. #2
    She likes the bike. But the ski gets her wet!!!! xlint89's Avatar
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    Welcome to the Hulk.

    1. You CAN. Some will argue all MUST be the same size/weight, while others will argue it's not a race boat. Can prob go .5mm over without any balance issues. Up to you.....

    2. I would split the cases. We're finding everyday that previous owners do REALLY silly chit......

    3. Doubt it.

    4. Heads mean nothing. What do the piston markings say? Gaskets used can also tell if it's been rebuilt.

    5. SLT's will not have a trim function, so No, they do not all use the same.

    However, you can use a MFD with trim and no have problem with it

  3. #3

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    Thanks for the info!

    It's looking like there has been engine work done in the past and the 189 hours on the MFD is probably not accurate. I'm thinking that I can't trust that anything was done correctly and will need to go completely through the engine and jet pump to make sure everything is okay. It's a long winter anyway...

    My MFD is missing the rubber button on the left side (select I think) but I can press on the circuit board beneth and it works. Does anyone know where I could get a button, possibly from a fried MFD?

    On the body, I was originally going to patch up the gelcoat damage, buff it out as best as I could and replace some of the trim items. However, I made the mistake of reading the Painting thread (which has some excellent information on the subject) and now I'm thinking about refinishing the gelcoat on the whole thing come spring.

  4. #4
    Quote Originally Posted by xlint89 View Post
    Welcome to the Hulk.

    1. You CAN. Some will argue all MUST be the same size/weight, while others will argue it's not a race boat. Can prob go .5mm over without any balance issues. Up to you.....

    2. I would split the cases. We're finding everyday that previous owners do REALLY silly chit......

    3. Doubt it.

    4. Heads mean nothing. What do the piston markings say? Gaskets used can also tell if it's been rebuilt.

    5. SLT's will not have a trim function, so No, they do not all use the same.

    However, you can use a MFD with trim and no have problem with it
    I have an 780 slt 1997 and my mfd decal has a picture of a waverunner on both sides of the top, along with -5 -4 -3 -2 -1 0 1 2 3 4 5, but no trim button. Does this mean that the mfd was replaced at some point? or do they all use the same decal?

  5. #5
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    That MFD will work on a ski that has trim. Thats just a trim position indicator. It moves with the trim motor when you use the handlebar switch.

  6. #6
    but i was just wondering if this means the MFD is not original, or if the SLTs use the same decal which has the trim markings...

  7. #7
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    Im guessing its not original

  8. #8
    She likes the bike. But the ski gets her wet!!!! xlint89's Avatar
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    Quote Originally Posted by bobbo268 View Post
    I have an 780 slt 1997 and my mfd decal has a picture of a waverunner on both sides of the top, along with -5 -4 -3 -2 -1 0 1 2 3 4 5, but no trim button. Does this mean that the mfd was replaced at some point? or do they all use the same decal?
    Yes, it was replaced with a model that had trim.

  9. #9
    Quote Originally Posted by xlint89 View Post
    Yes, it was replaced with a model that had trim.
    will have to call the dealership where this beast was serviced and hopefully they keep track of hours when they service, maybe this isn't a 235 hour ski after all (235 hours was written on the winterization tag from 2010 but we never actually checked the mfd, hmmmmm)

  10. #10
    BlueFishCrisis's Avatar
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    So many parts are interchangeable on these things that you never know what you really have....

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