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  1. #1

    SLT 780 engine options - pistons are a mess

    So I put the 96 SLT 780 to rest last season after having a good riding season. I had rebuilt the carbs and fuel pump that year changes all the fuel lines oil lines etc... I bought a compression tester this season just to see where I was at. The jet ski was running fine with speeds and RPMs where they were supposed to be (i have no clue how after pulling the heads). So I ran compression, MAG came up with 30 , Center 120 and PTO 123 . So I pulled the mag and it was nasty Ill post photos shortly. Decided to pull the other two and while not as bad they both have hot spots on them. My thought is that this is previous damage to the cylinders and not last season the fuel filter and carbs were bad when I did the rebuilds. Not sure if anyone can tell...

    I'm in need of advice for the next steps. My thoughts is to just buy a engine from SBT , but if there's cheaper alternatives I'm up for that also.

    I'm not sure whats involved in swapping the engine out, what parts I need to pull off the old motor etc..

    The head is from the mag with the most damaged piston of all.
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    thanks guys

  2. #2
    Banned User
    Join Date
    Jun 2010
    Milwaukee WI
    Depending on your wrenching ability, its actually cheaper to send out your crank to a crank shop, then have your cylinders bored and new pistons. Get everything back and reassemble it yourself.

  3. #3
    I'm not so worried about the wrenching, but the time required. I wouldn't mind tearing down I just don't know if I'll have the time to reassemble. Any thoughts on this being old or new damage, I imagine its hard if not impossible to tell. Thoughts on the sbt engine?

  4. #4 much for the 780? stimpsonjcat's Avatar
    Join Date
    Apr 2012
    Georgia - Lake Lanier - near 6TH
    I have done an SBT cylinder swap and I am currently reassembling a 780SLX with a crank from SBT.

    With that amount of damage I bet at least one crank bearing is destroyed.

    I haven't run into anything all that difficult about the tear-down and rebuild so far. In hind sight I am wishing I had torn down the second ski I got all the way.

    Oh and they look like they ran lean to me at some point. One tank of bad gas could do that damage. Or a loose fuel line maybe. something common to all 3 cylinders. Was the filter plugged? You say it was bad.

    The current wash patterns look pretty good to me.

  5. +1 by:

  6. #5
    I made the awful decision when I first got this ski to put it in the water and ride just because it started .... I had some bogging on acceleration towards the end of that season so last season I did what I should have from the start, fuel filter, oil filter, clean and rebuild carbs, rebuild fuel pump, change all the oil/fuel lines. All the right stuff. I didnt have a compression tester at the time so I just put her back in the water and she ran well but still had bogging. It didn't go away so I bought a tester this year and this is where I'm at now. My guess is that this happened from the start, but I can only guess

    On the road to recovery, I purchased a engine from sbt yesterday, I just don't have the time to do a full engine rebuild on my own, wish I did, last time I did a rebuild it was on a 1992 kawasaki. At this point I think the only thing I'm a little weary about is engine alignment. I think I'll stick with the oil injection, after rebuilding it seemed to be pumping pretty well.

    One other thing I noticed was sbt was selling bpr9es plugs with that engine, but I've always read and the service manual says to use the 8's. Any thoughts on that? Cooler spark to avoid detonation?

  7. #6
    BlueFishCrisis's Avatar
    Join Date
    Aug 2011
    Medina, Ohio, United States
    Spark plug info here:

    They may spec the 9s to try and keep away from Detonation...?

  8. #7
    Quote Originally Posted by BlueFishCrisis View Post
    Spark plug info here:

    They may spec the 9s to try and keep away from Detonation...?
    That's what I was thinking, The 1yr warranty is no fault so anything to keep people from sending it back I guess.

  9. #8
    RLACEMAN's Avatar
    Join Date
    Aug 2011
    Random Lake WI
    Make sure to go through the entire fuel system to make sure this doesn't happen again, anything to reduce fuel supply can cause this to happen. Also if the fuel you are using contains ethanol, with this engine you must use 89 or higher octane or this type of damage WILL happen again.

  10. #9
    Thanks rlaceman.

    Pulled the motor out last night to get ready for the swap. The starter motor while sounding strong has a good amount of rust on the outer casing, is this normal or should I look to replace the starter?

  11. #10
    BlueFishCrisis's Avatar
    Join Date
    Aug 2011
    Medina, Ohio, United States
    For the 20-$30 it will cost for a good used one, may want to just go ahead and do it. Take a good look at your bendix as well, specifically the retainer spring.....

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